Fluvial Landforms — Landforms Made by Running Water
›Running water = most important agent of denudation (p.47)
›In humid regions, running water is considered the most important geomorphic agent for land surface degradation. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›By doubling velocity, river's transporting power increases by 10x (p.49)
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Running water is the most important single agent of denudation — unlike glaciers (confined to cold latitudes), waves (only coastlines), or wind (mainly deserts). Rivers perform three tasks: erosion, transportation, and deposition. In humid regions, running water is the most important geomorphic agent for land degradation.
**River load types:** Materials in solution, suspended load (sand/silt/mud), traction load (pebbles/boulders rolled along bed).
**River erosion processes:** Corrasion/abrasion (mechanical grinding — lateral and vertical), Corrosion/solution (chemical dissolving), Hydraulic action (water pressure loosening rocks), Attrition (fragments wearing each other down). Overland flow also causes sheet erosion, which can concentrate into rills, then gullies, and eventually networks of valleys.
**Drainage patterns:** Dendritic (tree-like, on homogeneous rock), Trellised/Rectangular (on alternating hard/soft rock), Radial (outward from dome/volcano, e.g. Mt. Egmont, NZ), Centripetal (inward toward basin).
**Three stages of a river (landscape evolution):**
1. **Upper/Mountain course (Youth)**: Steep gradient, dominant vertical corrasion, V-shaped valley. Streams are few with poor integration, flowing over original slopes with shallow V-shaped valleys and no/narrow floodplains. Stream divides are broad and flat with marshes, swamps, and lakes. Meanders, if present, develop over upland surfaces and may entrench. Waterfalls and rapids may exist where local hard rock bodies are exposed.
2. **Middle/Valley course (Maturity)**: Lateral corrasion dominates, valley widening. Streams are plenty with good integration, and valleys are still V-shaped but deep. Trunk streams are broad enough to have wider floodplains where meanders are confined within the valley. The flat and broad inter-stream areas, swamps, and marshes of the youth stage disappear, and stream divides turn sharp. Waterfalls and rapids disappear.
3. **Lower/Plain course (Old Age)**: Deposition dominates. Smaller tributaries are few with gentle gradients. Streams meander freely over vast floodplains, showing natural levees and oxbow lakes. Divides are broad and flat with lakes, swamps, and marshes. Most of the landscape is at or slightly above sea level, eventually forming a peneplain (an almost plain) with low resistant remnants called monadnocks.
**Key erosional features:**
- **Valleys:** Start as rills, developing into gullies, then valleys. Types include V-shaped valleys, gorges, and canyons.
- **Gorge:** A deep valley with very steep to straight sides, almost equal in width at its top and bottom. Commonly forms in hard rocks (e.g., Valley of Kaveri river near Hogenekal).
- **Canyon:** Characterised by steep step-like side slopes, wider at its top than its bottom. Commonly forms in horizontal bedded sedimentary rocks (e.g., River Colorado in USA).
- **Potholes:** Circular depressions on rocky beds of hill-streams, formed by stream erosion and abrasion of rock fragments.
- **Plunge Pools:** Large, deep holes at the base of waterfalls, formed by the sheer impact of water and rotation of boulders.
- **Incised/Entrenched Meanders:** Very deep and wide meanders cut in hard rocks, found in streams flowing rapidly over steep gradients.
- **River Terraces:** Surfaces marking old valley floor or floodplain levels, resulting from vertical erosion by the stream into its own depositional floodplain. Can be paired (at same elevation on either side).
**Key depositional features:**
- **Alluvial Fans:** Form when streams from higher levels break into foot-slope plains, dumping coarse load as a cone-shaped deposit. Streams shift position, forming distributaries.
- **Deltas:** Deposition at river mouth when velocity decreases and load is dumped into the sea. Unlike alluvial fans, delta deposits are very well sorted with clear stratification. As deltas grow, river distributaries increase in length (e.g., Krishna River delta). Bird's foot delta (Mississippi), Arcuate/fan delta (Nile, Ganges), Estuarine delta (where tidal action is strong).
- **Floodplains:** A major landform of river deposition, where fine materials (sand, silt, clay) are deposited over the bed and when waters spill over banks during flooding. An active floodplain is the river bed; an inactive floodplain is above the bank. Floodplains in a delta are called delta plains.
- **Natural Levees:** Low, linear, parallel ridges of coarse deposits along the banks of large rivers.
- **Point Bars (Meander Bars):** Sediments deposited in a linear fashion on the concave side of meanders of large rivers.
- **Meanders:** Loop-like channel patterns over flood and delta plains. Meander is a channel pattern, not a landform. Caused by lateral working on banks, unconsolidated alluvial deposits, and Coriolis force. Active deposition occurs along the convex bank, while undercutting occurs along the concave bank (cut-off bank shows a steep scarp, convex bank has a gentle profile).
- **Oxbow Lakes:** Cut-off meander loops in the lower course, formed when deep loops are cut-off due to erosion at inflection points.
**Mississippi River** removes 2 million tonnes of eroded material into Gulf of Mexico daily (p.48).
All key facts
›Running water = most important agent of denudation (p.47)
›In humid regions, running water is considered the most important geomorphic agent for land surface degradation. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›By doubling velocity, river's transporting power increases by 10x (p.49)
›Irrawaddy drainage basin lowered by ~1/3 metre every 400 years (p.48)
›Victoria Falls, River Zambezi: 100m (360 feet) plunge — caused by fault-line scarp (p.51)
›Niagara Falls: 50m (167 feet) high — hard rock bar across valley (p.51)
›Kaieteur Falls, Guyana: 251m (825 feet) (p.51)
›Yosemite Falls, California: 780m (2,560 feet) total descent — hanging valley (p.51)
›Livingstone Falls, River Zaire: 270m (900 feet) through 30+ rapids (p.51)
›River capture terms: elbow of capture, wind gap, misfit stream, river piracy/beheading (p.50)
›Dendritic drainage = tree-like, on homogeneous rock (p.47)
›Trellised/rectangular drainage = on alternating hard/soft rocks (p.48)
›Radial drainage = from dome/cone — e.g. Mt. Egmont, New Zealand (p.48)
Arid and Desert Landforms
›Deserts confined mainly between 15°–30° N and S latitude (Trade Wind belt) (p.67)
›Sahara = largest hot desert: 9 million sq km (3.5 million sq miles) (p.173, Ch.18)
›Great Australian Desert = second largest hot desert (covers ~half Australia) (p.173)
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About one-fifth of the world's land is desert. Deserts lie mostly between 15°–30° N and S latitude (Trade Wind belts on western coasts), where descending air of subtropical high pressure belts prevails and offshore Trade Winds fail to bring moisture. Mid-latitude deserts (Gobi, Turkestan) are dry due to continental interiors, far from rain-bearing winds.
**Five types of desert landscape:**
1. **Hamada** (rocky desert): Large stretches of bare, swept rock; e.g. Hamada el Homra, Libya (~52,000 sq km)
2. **Reg** (stony desert): Angular pebbles and gravels; called **serir** in Libya/Egypt; **koum** in Turkestan = sandy
3. **Erg** (sandy desert): Sea of sand dunes; e.g. Calanscio Sand Sea, Libya; most iconic desert scenery
4. **Badlands**: Gully-eroded terrain; originally South Dakota, USA; e.g. Painted Desert, Arizona
5. **Mountain deserts**: Dissected highlands with wadis (dry valleys); e.g. Ahaggar Mountains, Tibesti Mountains, Sahara
**Wind erosion processes:** Deflation (lifting and blowing away loose materials), Abrasion (sand-blasting), Attrition (fragments wearing each other down)
**Wind erosion landforms:**
- Rock pedestals/Mushroom rocks (Gour in Sahara): Undercut near base by sand-blasting
- Zeugen: Tabular masses with hard layer over soft; ridges 3–30m; horizontal strata orientation
- Yardangs: Steep-sided ridges in vertical strata alignment with wind; corridors between; best in central Asia
- Mesas: Flat-top ped hard-capped hills; reduced to isolated buttes (e.g. Table Mountain, Cape Town is a mesa)
- Inselberg ('island-mountain'): Isolated steep-sided residual hills in old-age desert; granite/gneiss; e.g. N Nigeria, W Australia, Kalahari; Ayers Rock (Uluru) Australia
- Ventifacts/Dreikanter: Wind-faceted pebbles (3 faces = dreikanter); form desert pavement
- Deflation hollows: Qattara Depression, Sahara (135m below sea-level); Faiyum Depression, Egypt (40m below sea-level)
**Wind deposition features:**
- **Barchans**: Crescent-shaped mobile sand dunes; tips point downwind; most common
- **Seif dunes**: Long, knife-edged longitudinal dunes parallel to prevailing wind
- **Loess**: Fine wind-blown dust deposited beyond desert margins; extremely fertile; thick deposits in China's Loess Plateau (N China), also in Mississippi valley (prairie soils), Pampas (Argentina)
**Sahara Desert facts:** 5,150 km east-west, at least 1,600 km wide; total area 9 million sq km — larger than all 50 US states combined. Atacama (Peru/Chile) is driest — less than 13mm annual rainfall. One station received 0.5mm over 17 years.
All key facts
›Deserts confined mainly between 15°–30° N and S latitude (Trade Wind belt) (p.67)
›Sahara = largest hot desert: 9 million sq km (3.5 million sq miles) (p.173, Ch.18)
›Great Australian Desert = second largest hot desert (covers ~half Australia) (p.173)
›Hamada el Homra, Libya: ~52,000 sq km (20,000 sq miles) of rocky desert (p.67)
›Barchans = crescent/moon-shaped dunes, tips point downwind, most mobile
›Zeugen stands 3–30m above sunken furrows (p.69)
›Yardangs best developed in central Asia; also found in Atacama, Chile (p.69)
›Inselberg = German for 'island-mountain'; typical of N Nigeria, W Australia, Kalahari (p.70)
›Dreikanter = ventifact with 3 faceted surfaces (p.71)
›Loess from Sahara has been estimated to travel up to 3,700 km (2,300 miles) (p.71)
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Volcanism, Earthquakes, and Related Landforms
›Batholith = largest intrusive landform; usually granite; exposed by denudation (p.29)
›Laccolith = dome-shaped intrusion; e.g. Henry Mountains, Utah (p.28)
›Phacolith = lens-shaped at anticline crest or syncline trough; e.g. Corndon Hill, Shropshire (p.28)
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Volcanic activity creates both **intrusive** (plutonic) and **extrusive** (volcanic) landforms. Intrusive landforms form when magma solidifies within the crust; extrusive form when it reaches the surface. A volcano is a place where gases, ashes, and/or molten rock material (lava) escape to the ground. Magma refers to molten material within the upper mantle, while lava is molten material that reaches the earth's surface.
**Intrusive landforms:** Sill (horizontal intrusion along bedding planes), Dyke (vertical intrusion), Laccolith (dome-shaped mound, e.g. Henry Mountains, Utah), Lopolith (saucer-shaped, e.g. Bushveld, South Africa), Phacolith (lens-shaped at crest of anticline/trough of syncline), Batholith (huge granite mass — most spectacular, e.g. Wicklow Mountains Ireland, Main Range Malaysia). Intrusive forms are created when lava cools within the crustal portions.
**Types of lava:**
- Basic lava: Very fluid, ~1,000°C, dark, low silica, flows fast (16–48 km/h), builds shield/dome volcanoes with gentle slopes (e.g. Hawaiian volcanoes — Mauna Loa, Kilauea)
- Acid lava: Viscous, high silica, light-coloured, slow-flowing, forms steep-sided cones with violent explosions, pyroclasts/volcanic bombs; can form volcanic spine/plug (e.g. Mt. Pelee, Martinique)
**Types of volcanoes:**
- Shield/dome: Basic lava, gently sloping, wide (Hawaii). These are the largest volcanoes on Earth (barring basalt flows) and are characterized by low explosivity unless water enters the vent.
- Cinder/ash cone: Less fluid lava, steep, small (<300m), e.g. Mt. Nuevo (Naples), Mt. Paricutin (Mexico)
- Composite/strato-volcano: Most common and highest; built by alternating lava and ash layers from main conduit with parasitic cones; e.g. Mt. Vesuvius, Mt. Fuji, Mt. Etna, Mt. Stromboli, Mt. Popocatapetl. These volcanoes erupt cooler and more viscous lavas and often result in explosive eruptions, accumulating pyroclastic material and ashes in layers.
- **Caldera**: Large depression (several km across) formed by violent eruption and subsidence of volcano into magma below. Can form caldera lakes (e.g. Lake Toba, Sumatra; Crater Lake, Oregon). Calderas are formed by the collapse of highly explosive volcanoes.
- **Flood Basalt Provinces**: Outpour highly fluid lava that flows for long distances, covering thousands of square kilometers (e.g., Deccan Traps in India).
- **Mid-Ocean Ridge Volcanoes**: Occur in oceanic areas along mid-ocean ridges, with frequent eruptions in their central portions.
**Distribution:** ~500+ active volcanoes. Two-thirds in **Circum-Pacific Ring of Fire** (~100 Philippines, 70+ Indonesia, 40 Andes, 35 Japan). Mediterranean belt: Vesuvius, Etna, Stromboli. East African Rift Valley: Kilimanjaro, Kenya (extinct). **Himalayas have NO active volcanoes**.
**Geysers and Hot Springs:** Geysers erupt superheated steam/water to ~45m. Three main areas: Iceland, Rotorua (New Zealand), Yellowstone Park (USA). 'Old Faithful' at Yellowstone erupts every ~63 minutes.
**Earthquakes:** 50,000+ recorded annually. An earthquake is the shaking of the earth, caused by the release of energy along a fault. The point where energy is released is called the **focus** or **hypocentre**. The point on the surface nearest to the focus is the **epicentre**. Earthquake waves are of two main types: **body waves** (P-waves and S-waves) and **surface waves**. Body waves travel through the Earth's interior, while surface waves travel along the surface and are generally more destructive.
Tsunamis (Japanese term) = tidal waves caused by submarine earthquakes. 70% of earthquakes in Circum-Pacific belt; 20% in Mediterranean-Himalayan belt. Measured by seismograph. Earthquakes are scaled by **magnitude** (Richter scale, 0-10) and **intensity** (Mercalli scale, 1-12).
All key facts
›Batholith = largest intrusive landform; usually granite; exposed by denudation (p.29)
›Laccolith = dome-shaped intrusion; e.g. Henry Mountains, Utah (p.28)
›Phacolith = lens-shaped at anticline crest or syncline trough; e.g. Corndon Hill, Shropshire (p.28)
›Lopolith = saucer-shaped; e.g. Bushveld Lopolith, Transvaal, South Africa (p.28)
›Acid lava is viscous, can form spine/plug — e.g. Mt. Pelee spine rose 300m by 1903 (p.29)
›Mt. Stromboli = 'Lighthouse of the Mediterranean' due to frequent glowing eruptions (p.30)
›Krakatoa (Sunda Strait, between Java and Sumatra) erupted 1883: 2/3 of island collapsed into caldera; explosion heard 4,800 km away in Australia; tsunami killed 36,000 (p.31)
›Anak Krakatoa ('Child of Krakatoa') — new island appeared in 1927 (p.31)
›Mt. Pelee, Martinique 1902: Nuee ardente (glowing avalanche) destroyed St. Pierre, 30,000 killed in minutes (p.32)
›Vesuvius 79 AD: Pompeii buried under 6m volcanic ash; Herculaneum under 15m mud-flow (p.31)
›Ring of Fire contains ~2/3 of world's volcanoes; extends 3,200 km from Aleutians through Japan, Philippines, Indonesia to New Zealand (p.32)
Permafrost
›Permafrost describes the permanently frozen sub-soil in tundra lands. (p. 237)
›In polar climates, water in the soil is frozen to great depths. (p. 233)
›Summer heat can only thaw the upper 150 mm (6 inches) of the soil. (p. 233)
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Permafrost refers to the permanently frozen sub-soil found in tundra regions, primarily north of the Arctic Circle. This condition results from the extremely low mean annual temperatures characteristic of the polar climate, where the ground remains solidly frozen for most of the year. During the brief summer, the upper layer of the soil may thaw, but typically only to a depth of about 150 mm (6 inches), leaving the ground frozen to great depths underneath.
The presence of permafrost significantly influences the physical environment. It contributes to poor drainage in the tundra lowlands, as the frozen sub-soil prevents water from percolating downwards, leading to the formation of ponds, marshes, and waterlogged areas in hollows. This permanently frozen sub-soil is also a crucial factor limiting plant growth, particularly trees, as it makes the ground inaccessible to deep roots for all but a few months and forces shallow roots to grow laterally near the surface.
All key facts
›Permafrost describes the permanently frozen sub-soil in tundra lands. (p. 237)
›In polar climates, water in the soil is frozen to great depths. (p. 233)
›Summer heat can only thaw the upper 150 mm (6 inches) of the soil. (p. 233)
›The ground remains solidly frozen for all but four months of the year, making it inaccessible to plants. (p. 233)
›Poor drainage in the tundra is usually due to the sub-soil being permanently frozen. (p. 235)
›The permanently frozen sub-soil is a reason for the shallow, lateral root growth of stunted trees in tundra regions. (p. 237)
Scope and Importance of Physical Geography
›Physical geography includes the study of the lithosphere, atmosphere, hydrosphere, and biosphere.
›The lithosphere involves landforms, drainage, relief, and physiography.
›The atmosphere covers its composition, structure, weather and climate elements (temperature, pressure, winds, precipitation), and climatic types.
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Physical geography encompasses the study of the Earth's natural environment, including its various realms: the lithosphere, atmosphere, hydrosphere, and biosphere. The lithosphere involves the study of landforms, drainage, relief, and physiography. The atmosphere focuses on its composition, structure, elements and controls of weather and climate, such as temperature, pressure, winds, and precipitation, along with climatic types. The hydrosphere covers the realm of water on Earth's surface, including oceans, seas, lakes, and associated water features. The biosphere deals with all life forms, including human beings and macro-organisms, their sustaining mechanisms like food chains, ecological parameters, and ecological balance. Soils, formed through pedogenesis, are also a crucial part of its study, considering parent rocks, climate, biological activity, and time.
The importance of physical geography stems from the fact that each of these elements is vital for human beings. Landforms provide the base for human activities, with plains used for agriculture, plateaus for forests and minerals, and mountains offering pastures, forests, tourist spots, and river sources. Climate significantly influences human aspects like housing, clothing, food habits, vegetation, cropping patterns, livestock farming, and certain industries. Precipitation, for instance, recharges groundwater aquifers essential for agriculture and domestic use. Oceans are recognized as vast storehouses of resources, including fish, seafood, and minerals. Soils are renewable resources that underpin agriculture and accommodate the biosphere. Thus, physical geography is critical for evaluating and managing natural resources, requiring an understanding of the intricate relationship between the physical environment and human activities to achieve sustainable development, especially in light of ecological imbalances caused by accelerated resource utilization.
All key facts
›Physical geography includes the study of the lithosphere, atmosphere, hydrosphere, and biosphere.
›The lithosphere involves landforms, drainage, relief, and physiography.
›The atmosphere covers its composition, structure, weather and climate elements (temperature, pressure, winds, precipitation), and climatic types.
›The hydrosphere studies water bodies like oceans, seas, and lakes on the Earth's surface.
›The biosphere deals with life forms, food chains, ecological parameters, and ecological balance.
›Soils are formed through pedogenesis, influenced by parent rocks, climate, biological activity, and time.
›Landforms provide the base for human activities; plains are for agriculture, plateaus for forests and minerals, and mountains for pastures, forests, tourist spots, and river sources.
›Climate influences house types, clothing, food habits, vegetation, cropping patterns, livestock farming, and industries.
›Precipitation recharges groundwater aquifers, vital for agriculture and domestic use.
›Oceans are storehouses of resources, including fish, seafood, and mineral resources.
›Soils are renewable resources influencing economic activities like agriculture and providing a basis for the biosphere.
›The study of physical geography is important for evaluating and managing natural resources.
Ocean Salinity, Tides, and Water Properties
›Average ocean salinity: 35 ppt (35 grams per kilogram of seawater)
›Salinity is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater, expressed as parts per thousand (o/oo or ppt).
›Average salinity of the Indian Ocean is 35 o/oo.
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**Ocean Salinity:**
Salinity is the total amount of dissolved salts in seawater, expressed in parts per thousand (ppt or ‰). The average salinity of the world's oceans is about 35 ppt.
Factors affecting salinity:
- Evaporation: Higher evaporation increases salinity (sub-tropical zones are most saline)
- Precipitation and river inflow: Dilute salinity (equatorial zone, river mouths)
- Freezing and melting of ice: Freezing leaves behind salt (increases salinity in polar waters); melting dilutes
- Ocean currents: Mix waters of different salinities
- Wind: Influences salinity by transferring water to other areas.
Horizontal distribution: Salinity varies from about 33–37 ppt in open oceans. Sub-tropical regions (Mediterranean, Red Sea) have highest salinity. Polar regions and river mouths have lowest salinity. The Dead Sea (a landlocked lake) has extremely high salinity (~340 ppt). Other highly saline water bodies include Lake Van in Turkey and the Great Salt Lake in Utah. Salinity can reach up to 70 o/oo in hot and dry regions with high evaporation. The North Sea records higher salinity due to the North Atlantic Drift, while the Black Sea has very low salinity due to large freshwater influx. The Bay of Bengal shows a low salinity trend due to river water influx, contrasting with the Arabian Sea which shows higher salinity due to high evaporation and low freshwater influx. The Atlantic Ocean's average salinity is around 36 o/oo, with a maximum of 37 o/oo between 20° N and 30° N and 20° W - 60° W. In the Pacific Ocean, salinity decreases on the western parts of the northern hemisphere due to melted Arctic water, and similarly south of 15°-20° S.
Vertical distribution: Salinity generally increases with depth up to the halocline (zone of rapid salinity change), then remains relatively constant in deeper waters. Salinity at depth is fixed, as water is not lost and salt is not added. Lower salinity water rests above higher salinity dense water. Increasing salinity causes seawater density to increase, leading to high salinity water sinking below lower salinity water and creating stratification by salinity.
**Tides:**
Tides are the periodic rise and fall of sea levels caused by the gravitational pull of the Moon and the Sun on Earth's oceans.
Tides are mainly caused by the gravitational pull of the Sun and the Moon, and additionally by the centrifugal force which counterbalances gravity. Together, these forces create two major tidal bulges on the Earth.
- Spring tides: Occur when the Sun, Moon, and Earth are aligned (new moon and full moon). Gravitational forces of Moon and Sun combine — highest high tides and lowest low tides.
- Neap tides: Occur when the Sun and Moon are at right angles to each other (first and third quarter of moon). Forces partially cancel — moderate tides.
The Moon's gravitational pull is approximately 2.17 times more effective than the Sun's in generating tides (despite the Sun being much more massive, the Moon is much closer).
Two high tides and two low tides occur approximately every 24 hours 52 minutes in most coastal locations (semidiurnal tides), though some locations have diurnal (once daily) tides.
Tidal bulges gain greater height on wide continental shelves and become lower when hitting mid-oceanic islands. The shape of bays and estuaries, particularly funnel-shaped ones, can greatly magnify tidal intensity.
Tidal bores occur in funnel-shaped estuaries where the incoming tide is funnelled into a narrow channel, creating a wave that travels upstream (e.g., Hugli river in West Bengal).
All key facts
›Average ocean salinity: 35 ppt (35 grams per kilogram of seawater)
›Salinity is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater, expressed as parts per thousand (o/oo or ppt).
›Average salinity of the Indian Ocean is 35 o/oo.
›Salinity of 24.7 o/oo is considered the upper limit to demarcate 'brackish water'.
›Sodium chloride constitutes about 77.7% of total dissolved salts in seawater
›Red Sea has the highest salinity among major seas (~41 ppt) due to high evaporation and no rivers.
›**Note on Contradiction**: The existing content states Dead Sea salinity is ~340 ppt, NCERT states 238 o/oo, while GC Leong states 250 per thousand.
›Baltic Sea has the lowest salinity among seas (~7–8 ppt) due to heavy river inflow and low evaporation.
›Lake Van in Turkey (330 o/oo) and Great Salt Lake (220 o/oo) are among the water bodies with the highest salinity.
›In hot and dry regions, where evaporation is high, salinity can sometimes reach 70 o/oo.
›The North Sea records higher salinity due to more saline water brought by the North Atlantic Drift.
›Black Sea has very low salinity due to enormous fresh water influx by rivers.
Ocean Currents — Types, Causes, and Significance
›The Gulf Stream transports more water than all the world's rivers combined
›Cold currents on western coasts cause coastal deserts (Atacama, Namib, Sonoran)
›Warm currents on eastern coasts bring rainfall and moderate temperatures
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Ocean currents are continuous, directed movements of seawater, often described as "river flow in oceans". They are of two types: surface currents (driven by winds, salinity differences, and temperature) and deep-water currents (thermohaline circulation, driven by differences in water density due to temperature and salinity). These movements are influenced by both primary forces that initiate the water's motion and secondary forces that shape their flow paths.
**Causes of Ocean Currents:**
1. **Planetary winds**: Trade winds drive equatorial currents westward; westerlies drive mid-latitude currents eastward
2. **Temperature differences**: Warm water at equator, cold at poles — creates density differences; heating by solar energy causes water to expand, resulting in higher water levels near the equator (approx. 8 cm higher) which creates a slight gradient for flow.
3. **Salinity differences**: Higher salinity = higher density; sinks and moves as deep currents. Denser water tends to sink, while lighter water tends to rise.
4. **Earth's rotation (Coriolis effect)**: Deflects currents clockwise in Northern Hemisphere, anti-clockwise in Southern Hemisphere — creates large gyres. It causes warm currents from low latitudes to move right in the Northern Hemisphere and left in the Southern Hemisphere.
5. **Shape of coastline**: Coastlines redirect ocean currents
6. **Gravity**: Tends to pull water down piles and create gradient variation.
**Warm and Cold Currents:**
- Warm currents flow from tropical to polar regions; Cold currents flow from polar to tropical regions
- Warm currents: North Atlantic Drift (Gulf Stream extension), Kuroshio (Japan), Brazilian Current. Warm currents are usually observed on the east coast of continents in low and middle latitudes (both hemispheres) and on the west coasts of continents in high latitudes (Northern Hemisphere).
- Cold currents: Labrador Current, California Current, Benguela Current, Humboldt (Peru) Current, Canary Current. Cold currents are usually found on the west coast of continents in low and middle latitudes (both hemispheres) and on the east coast in higher latitudes (Northern Hemisphere).
**Major Ocean Current Gyres:**
- North Atlantic Gyre (clockwise): Gulf Stream → North Atlantic Drift → Canary Current → North Equatorial Current
- South Atlantic Gyre (anti-clockwise): Brazil Current → Benguela Current → South Equatorial Current
- North Pacific Gyre: Kuroshio → North Pacific Drift → California Current
- Indian Ocean: Seasonal reversal due to monsoon
**Significance:**
- Warm currents: Moderate climates on adjacent coasts; increase precipitation; reduce fog. On west coasts of continents in middle and higher latitudes, they cause a distinct marine climate with cool summers and relatively mild winters.
- Cold currents: Cool and dry coastal climates (deserts on west coasts — Namib, Atacama); create upwelling zones → nutrient-rich waters → fishing grounds. West coasts of continents in tropical and subtropical latitudes are bordered by cool waters, leading to low average temperatures, narrow diurnal/annual ranges, fog, and generally arid conditions.
- Fishing grounds: Where warm and cold currents meet (Grand Banks — Labrador + Gulf Stream; Japan's Fishing Grounds — Kuroshio + Oyashio). The mixing of warm and cold currents replenishes oxygen and favors plankton growth, which are primary food for fish.
All key facts
›The Gulf Stream transports more water than all the world's rivers combined
›Cold currents on western coasts cause coastal deserts (Atacama, Namib, Sonoran)
›Warm currents on eastern coasts bring rainfall and moderate temperatures
›The Labrador Current and Gulf Stream meet near Newfoundland — Grand Banks (major fishing ground)
›The Humboldt (Peru) Cold Current creates the Atacama Desert on South America's west coast
›El Niño is a periodic warming of the eastern Pacific (weakening of trade winds) that disrupts normal ocean current patterns
›Indian Ocean currents reverse direction with the monsoon seasons
›Thermohaline circulation (ocean conveyor belt) drives deep ocean circulation
›Water in ocean currents moves ahead from one place to another, unlike waves where only energy moves.
›Ocean currents are influenced by primary forces (heating by solar energy, wind, gravity, Coriolis force) that initiate movement, and secondary forces that influence their flow. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Near the equator, ocean water is about 8 cm higher in level than in the middle latitudes due to heating by solar energy, creating a slight gradient for water flow. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
Wind Erosion Processes in Deserts
›Wind is more efficient as an agent of erosion, transportation, and deposition in arid regions than in humid regions. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›The effectiveness of wind erosion is almost unrestrained in deserts due to little vegetation or moisture to bind loose surface materials. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Deflation** is the lifting and blowing away of loose materials from the ground. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
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In arid regions, wind acts as a significant agent of erosion, transportation, and deposition, becoming more efficient in deserts compared to humid areas due to the scarcity of vegetation and moisture that would otherwise bind loose surface materials. This absence allows the effects of wind erosion to be largely unrestrained. The primary mechanics of wind erosion include deflation, abrasion, and attrition, which collectively shape the distinctive desert landscape.
Deflation is the process where wind lifts and blows away loose materials, such as unconsolidated sand and pebbles, leading to the lowering of the land surface and the formation of large depressions known as deflation hollows. Abrasion involves the sand-blasting of rock surfaces, where wind hurls sand particles against them, causing the surfaces to be scratched, polished, and worn away, most effectively near the base of rocks. Attrition occurs when wind-borne particles collide with each other, causing them to wear down, reduce in size, and become rounded. These combined processes result in a variety of characteristic desert landforms.
All key facts
›Wind is more efficient as an agent of erosion, transportation, and deposition in arid regions than in humid regions. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›The effectiveness of wind erosion is almost unrestrained in deserts due to little vegetation or moisture to bind loose surface materials. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Deflation** is the lifting and blowing away of loose materials from the ground. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Deflation can remove finer dust and sand kilometers away, even outside desert margins. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Deflation results in the lowering of the land surface to form large depressions called deflation hollows, such as the Qattara Depression. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Abrasion** is the sand-blasting of rock surfaces by winds hurling sand particles against them, causing scratching, polishing, and wearing away. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Abrasion is most effective at or near the base of rocks where the wind carries the greatest amount of material. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Attrition** is the process where wind-borne particles collide and wear each other away, reducing their size and rounding them into shapes like millet seed sand. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
Plate Tectonics and Distribution of Continents
›The Earth's lithosphere is divided into several major and minor plates
›Divergent boundaries: mid-Atlantic Ridge (plates moving apart), new oceanic crust forms
›Convergent boundaries: oceanic-continental collision creates subduction zones and volcanic arcs; continental-continental collision creates fold mountains (Himalayas)
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Plate tectonics explains the large-scale movement of Earth's lithospheric plates, leading to the formation of mountain systems, ocean trenches, volcanic arcs, and earthquake belts. The Earth's outer shell is divided into a series of rigid plates that float on the semi-molten asthenosphere beneath.
The continents and ocean floors are products of the movement of these plates. Where plates move apart (divergent boundaries), new oceanic crust is formed at mid-ocean ridges. Where plates collide (convergent boundaries), one plate may subduct beneath the other, creating deep ocean trenches and volcanic mountain chains. Where plates slide past each other (transform boundaries), fault zones develop.
The theory emerged from earlier ideas of continental drift proposed by Alfred Wegener. Evidence for plate tectonics includes: the matching coastlines of continents, identical fossil records on continents now separated by oceans, matching geological structures across continents, paleoclimatic evidence, and the distribution of earthquake and volcanic zones.
The Himalayas formed through the collision of the Indo-Australian plate with the Eurasian plate. The Deccan Plateau represents a remnant of the ancient Gondwana supercontinent. The Andes and Rockies formed at subduction zones along the western edges of the American continents.
All key facts
›The Earth's lithosphere is divided into several major and minor plates
›Divergent boundaries: mid-Atlantic Ridge (plates moving apart), new oceanic crust forms
›Convergent boundaries: oceanic-continental collision creates subduction zones and volcanic arcs; continental-continental collision creates fold mountains (Himalayas)
›Transform boundaries: San Andreas Fault (California) is a classic example
›The Himalayan mountain system is a result of the collision of the Indian plate with the Eurasian plate
›The Deccan Plateau basalts were formed by extensive volcanic activity associated with the break-up of Gondwanaland
›Over 97% of earthquakes and volcanic activity occur along plate boundaries
›The circum-Pacific belt ("Ring of Fire") is the most seismically and volcanically active zone
›Continents cover 29 percent of the surface of the earth.
›Abraham Ortelius, a Dutch map maker, first proposed the possibility of continents being joined as early as 1596.
›Alfred Wegener, a German meteorologist, put forth "the continental drift theory" in 1912 regarding the distribution of oceans and continents.
›According to Wegener, all continents formed a single supercontinent named PANGAEA ("all earth") and a mega-ocean called PANTHALASSA ("all water").
›
Geomorphic Processes — Weathering, Erosion, and Landform Evolution
›Weathering is in situ; erosion involves transportation of material
›Chemical weathering is dominant in hot, humid conditions (tropical India)
›Physical weathering dominates in cold, arid regions (Himalayas, Rajasthan)
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Geomorphic processes are the internal (endogenic) and external (exogenic) forces that continuously modify the Earth's surface. Endogenic processes originate from within the Earth — including volcanism, earthquakes, and tectonic movements — and tend to build up relief. Exogenic processes are driven by forces at or near the Earth's surface — including weathering, erosion, transportation, and deposition — and tend to wear down relief.
Weathering is the process of disintegration and decomposition of rocks in situ (in place), without any transport. It is of three types:
1. **Physical (Mechanical) Weathering**: Breakdown of rocks by temperature changes, freeze-thaw cycles, and pressure release without chemical change. Block disintegration, exfoliation, and granular disintegration are major types.
2. **Chemical Weathering**: Decomposition of rocks through chemical reactions such as oxidation, hydration, carbonation, and solution. Prevalent in humid tropical climates (like much of India).
3. **Biological Weathering**: Disintegration or decomposition caused by plants, animals, and microorganisms.
Erosion involves the wearing away of the land surface by running water (fluvial erosion), glaciers (glacial erosion), wind (aeolian erosion), and waves (marine erosion). Each agent creates distinctive landforms.
Mass movement refers to the downslope movement of weathered material under the influence of gravity — including landslides, rockfalls, soil creep, and mudflows.
All key facts
›Weathering is in situ; erosion involves transportation of material
›Chemical weathering is dominant in hot, humid conditions (tropical India)
›Physical weathering dominates in cold, arid regions (Himalayas, Rajasthan)
›Running water is the most important agent of erosion in India
›Wind erosion is significant in arid zones (Rajasthan, Kachchh)
›Glacial erosion creates U-shaped valleys, cirques, horns, and aretes (typical of high Himalayas)
›Loess deposits are formed by wind deposition of fine particles
›The Gangetic plains are largely formed by fluvial deposition
›Geomorphic agents are mobile mediums (like running water, moving ice masses, wind, waves and currents) which remove, transport, and deposit earth materials.
›Gravity, besides being a directional force activating all downslope movements, also causes stresses on earth materials; without gravity and gradients, no erosion, transportation, and deposition are possible.
›The energy for endogenic geomorphic processes is mostly generated by radioactivity, rotational and tidal friction, and primordial heat from the origin of the earth.
Wind Depositional Landforms (Deserts)
›Materials eroded and transported by winds eventually come to rest, forming depositional landforms (ch07).
›Finest dust can travel thousands of kilometers and be deposited outside desert margins, sometimes falling as 'blood rains' in distant regions (ch07).
›Dust from the Sahara Desert has been known to be blown across the Mediterranean to Italy or Switzerland (ch07).
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Wind depositional landforms in deserts result from the accumulation of materials eroded and transported by wind. While the finest dust can travel enormous distances, even beyond desert limits, coarser sands are too heavy and remain within the desert, forming distinct depositional features. The migration and shaping of these landforms are influenced by factors such as particle size, wind direction and velocity, the nature of the surface, and the presence of water or vegetation.
The primary wind depositional landforms are dunes and loess. Dunes are hills of sand shaped by wind movement, found predominantly in sandy deserts (ergs). They can be active, constantly moving, or inactive, stabilized by vegetation. Two significant types of dunes are barchans and seifs. Barchans are crescentic, live dunes that advance steadily, exhibiting a convex, gently sloping windward side and a concave, steep leeward (slip-face) side. Seifs, or longitudinal dunes, are long, narrow sand ridges that align parallel to the prevailing winds, often extending over a hundred kilometers and reaching heights of more than 60 meters.
Loess refers to the fine, wind-blown dust deposited beyond desert boundaries, typically yellow, friable, and fertile. It is a porous loam, rich in lime, where water easily infiltrates, leaving the surface dry. Extensive loess deposits can be found in regions like north-west China, where dust from the Gobi Desert has accumulated to significant depths, forming the 'Huangtu' or yellow earth. Similar deposits are also found in parts of Europe and the U.S.A.
All key facts
›Materials eroded and transported by winds eventually come to rest, forming depositional landforms (ch07).
›Finest dust can travel thousands of kilometers and be deposited outside desert margins, sometimes falling as 'blood rains' in distant regions (ch07).
›Dust from the Sahara Desert has been known to be blown across the Mediterranean to Italy or Switzerland (ch07).
›Dust from the Gobi Desert has accumulated in the Huang He (Hwang Ho) basin to depths of several hundred meters over centuries (ch07).
›Coarser sands are too heavy to be blown out of desert limits and remain within, forming dunes or other depositional features (ch07).
›The migration pattern of wind-borne materials depends on particle size, wind direction and velocity, surface characteristics, and the presence of water or vegetation (ch07).
›**Dunes** are hills of sand formed by accumulation and shaped by wind movements (ch07).
›Dunes can be 'active' (live dunes, constantly moving) or 'inactive' (fixed dunes, rooted with vegetation) (ch07).
›Dunes are most prominent in erg deserts (sandy deserts) (ch07).
›Many fanciful names exist for dunes based on their shape, size, and alignment, including star dune, pyramidal dune, and transverse dune (ch07).
›**Barchans (Barkhan)** are crescentic dunes, occurring individually or in groups, that advance steadily with prevailing winds (ch07, Fig. 7.6).
Earth, Universe, and the Solar System
›Equatorial circumference: 40,084 km; Polar circumference: 133 km less (p.1)
›Equatorial diameter: 12,761 km; Polar diameter: 42 km shorter (p.1)
›Moon is 384,629 km from Earth; light takes 1 second to reach us (p.1)
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The Earth is one of nine planets revolving around the Sun in elliptical orbits. The solar system is part of the Milky Way galaxy, which alone contains about 100,000 million stars. The Earth is not a perfect sphere — it is slightly flattened at the poles and bulges at the equator, making it a **geoid**. Its equatorial diameter (12,761 km) is 42 km more than its polar diameter. The Earth is about 4,500 million years old.
The Earth completes one rotation on its axis in approximately 24 hours (solar day) and one revolution around the Sun in 365¼ days. The Earth's axis is tilted at 23½° to the plane of its orbit, which causes the seasons and variation in day length throughout the year.
Key consequences of Earth's motions:
- **Rotation**: Causes day and night, deflection of winds (Coriolis effect), difference in time between meridians
- **Revolution + Tilt**: Causes seasons, variation in the length of day and night, and the apparent movement of the sun
All key facts
›Equatorial circumference: 40,084 km; Polar circumference: 133 km less (p.1)
›Equatorial diameter: 12,761 km; Polar diameter: 42 km shorter (p.1)
›Moon is 384,629 km from Earth; light takes 1 second to reach us (p.1)
›Sun is 300,000 times bigger than Earth; surface temperature 6,000°C (p.1)
›Light from Sun takes 8 minutes to reach Earth (p.1)
›Earth's axis inclined at 23½° to orbital plane — cause of seasons (Ch.1)
›Perihelion: Earth closest to Sun (Jan 3); Aphelion: farthest (July 4)
›Tropic of Cancer: 23½°N; Tropic of Capricorn: 23½°S; Arctic Circle: 66½°N
›At equinoxes (Mar 21, Sep 23): day and night equal everywhere
›At solstices (Jun 21, Dec 22): maximum tilt toward/away from Sun
›Nine planets in order from Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto (per 3rd ed.)
›Jupiter is the largest planet; Mercury is the smallest and closest to Sun
›Uranus rotates clockwise (east to west), unlike other planets
›Saturn has three rings and nine satellites
›The Milky Way galaxy contains ~100,000 million stars (p.1)
›The most popular argument for the origin of the universe is the Big Bang Theory, also known as the expanding universe hypothesis. (ch02-fundamentals-of-physical-geography.md, p.12)
›Edwin Hubble provided evidence in 1920 that the universe is expanding. (ch02-fundamentals-of-physical-geography.md, p.12)
›The Big Bang event is generally accepted to have taken place 13.7 billion years before the present. (ch02-fundamentals-of-physical-geography.md, p.14)
›The formation of stars is believed to have taken place some 5-6 billion years ago. (ch02-fundamentals-of-physical-geography.md, p.14)
›A light year is a measure of distance, where light travels at 300,000 km/second, equaling 9.461×10^12 km in one year. (ch02-fundamentals-of-physical-geography.md, p.14)
›The mean distance between the sun and the earth is 149,598,000 km, which is 8.311 minutes in terms of light years. (ch02-fundamentals-of-physical-geography.md, p.14)
›Initially, the planet Earth was a barren, rocky, hot object with a thin atmosphere of hydrogen and helium. (ch02-fundamentals-of-physical-geography.md, p.15)
›The process of differentiation caused earth-forming material to separate into different layers (crust, mantle, outer core, inner core) based on density. (ch02-fundamentals-of-physical-geography.md, p.15)
›The primordial atmosphere (hydrogen and helium) of terrestrial planets was stripped off by solar winds. (ch02-fundamentals-of-physical-geography.md, p.15)
›The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia, and very little free oxygen, released through a process called degassing from Earth's interior. (ch02-fundamentals-of-physical-geography.md, p.15)
›The Earth's oceans were formed within 500 million years from the formation of the earth, making them approximately 4,000 million years old. (ch02-fundamentals-of-physical-geography.md, p.16)
›The process of photosynthesis evolved around 2,500-3,000 million years before the present. (ch02-fundamentals-of-physical-geography.md, p.16)
›Oxygen began to flood the atmosphere approximately 2,000 million years ago. (ch02-fundamentals-of-physical-geography.md, p.16)
›Life began to evolve sometime around 3,800 million years ago. (ch02-fundamentals-of-physical-geography.md, p.16)
Formation of Lakes by Volcanic Activity
›**Crater and Caldera Lakes:** Form when the hollows (craters or enlarged calderas) left by volcanic explosions or subsidence in dormant/extinct volcanoes fill with rainwater, lacking superficial outlets.
›Examples: Crater Lake in Oregon, U.S.A. (occupies a caldera); Lake Toba in northern Sumatra; Lake Avernus near Naples.
›**Lava-Blocked Lakes:** Occur when a stream of lava flows across a valley, solidifies, and dams a river, causing water to accumulate and form a lake.
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Lakes formed by volcanic activity arise from several distinct processes related to eruptions and subsequent geological changes. One primary method involves the formation of **crater and caldera lakes**. During a volcanic explosion, the summit of a cone may be ejected, leaving a natural depression known as a crater. This crater can subsequently enlarge through subsidence, forming a caldera. In dormant or extinct volcanoes, these depressions, which are typically dry, steep-sided, and roughly circular, accumulate rainwater due to the absence of superficial outlets, thus forming a lake.
Another way volcanic lakes are created is through **lava-blocked lakes**. In active volcanic areas, molten lava flowing across a valley can solidify, creating a natural dam. This dam then obstructs the flow of a river, leading to the accumulation of water behind it and the formation of an elongated lake.
Finally, lakes can also form due to the **subsidence of a volcanic land surface**. This occurs when the crust of a hollow lava flow collapses, resulting in a wide and shallow depression that can subsequently fill with water to become a lake.
All key facts
›**Crater and Caldera Lakes:** Form when the hollows (craters or enlarged calderas) left by volcanic explosions or subsidence in dormant/extinct volcanoes fill with rainwater, lacking superficial outlets.
›Examples: Crater Lake in Oregon, U.S.A. (occupies a caldera); Lake Toba in northern Sumatra; Lake Avernus near Naples.
›**Lava-Blocked Lakes:** Occur when a stream of lava flows across a valley, solidifies, and dams a river, causing water to accumulate and form a lake.
›Example: A lava flow blocking the Jordan valley formed the Sea of Galilee, which is an elongated inland lake.
›**Lakes due to Subsidence of a Volcanic Land Surface:** Result from the collapse of the crust of a hollow lava flow, creating wide and shallow depressions that can host lakes.
›Example: Myvatn of Iceland.
Man-made and Biological Lakes
›**Man-made lakes** are artificial lakes created by humans. (ch09-lakes.md, p. 85)
›They are typically formed by **erecting concrete dams** across river valleys to create **reservoirs**. (ch09-lakes.md, p. 85)
›An imposing example of a man-made lake is **Lake Mead**, located above the Hoover Dam on the Colorado River, U.S.A. (ch09-lakes.md, p. 85)
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Man-made lakes, also known as artificial lakes, are created by human activities, primarily through the construction of concrete dams across river valleys. These dams hold back river water to form reservoirs. A prominent example is Lake Mead, formed by the Hoover Dam on the Colorado River in the U.S.A. Beyond damming, human activities such as mining (e.g., tin mining in Peninsular Malaysia) and the creation of ornamental or fishing lakes also contribute to the formation of man-made lakes.
Biological lakes are those formed due to the activities of animals. Beavers, for instance, are known to construct dams across rivers using timber. These beaver dams create relatively permanent lakes, such as Beaver Lake in Yellowstone National Park, U.S.A.
Both natural and artificial lakes serve vital human purposes. Man-made lakes, specifically, are crucial for domestic water supply to towns and industrial cities, especially in regions lacking natural lakes. They are also utilized for generating hydro-electric power, often as 'man-made reservoirs' in mountainous districts. Multi-purpose dams that form these lakes further supply water for irrigation and are constructed to control floods by absorbing excess water during heavy rains. Additionally, artificial lakes are created for inland fish breeding in many countries.
All key facts
›**Man-made lakes** are artificial lakes created by humans. (ch09-lakes.md, p. 85)
›They are typically formed by **erecting concrete dams** across river valleys to create **reservoirs**. (ch09-lakes.md, p. 85)
›An imposing example of a man-made lake is **Lake Mead**, located above the Hoover Dam on the Colorado River, U.S.A. (ch09-lakes.md, p. 85)
›Other human activities leading to lake formation include **mining operations** (e.g., tin mining in Peninsular Malaysia), and the creation of **ornamental lakes** (e.g., Lake Gardens in Kuala Lumpur, Taiping Lakes) and **fishing-lakes** for inland fish culture. (ch09-lakes.md, p. 85)
›Man-made lakes and reservoirs serve as **sources of domestic water supply** for surrounding towns and industrial cities. (ch09-lakes.md, p. 85)
›They are used to generate **hydro-electric power**, furnishing a good head of water. (ch09-lakes.md, p. 86)
›**Modern multi-purpose dams** (forming man-made lakes) also supply water for **irrigation**. (ch09-lakes.md, p. 86)
›**Artificial reservoirs** are constructed to **control floods** in areas where natural lakes are insufficient. (ch09-lakes.md, p. 86)
›**Biological lakes** are made by animals, such as beavers constructing dams across rivers with timber. (ch09-lakes.md, p. 85)
›**Beaver dams** are quite permanent. (ch09-lakes.md, p. 85)
›An example of a lake made by animals is **Beaver Lake** in Yellowstone National Park, U.S.A. (ch09-lakes.md, p. 85)
Islands and Coral Reefs
›Sri Lanka separated from India by Palk Strait (p.97)
›Tasmania separated from Australia by Bass Strait (p.97)
›Malagasy separated from Africa by Mozambique Channel (p.97)
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Islands are classified into **Continental islands** (once part of mainland, separated by rise in sea-level or land subsidence) and **Oceanic islands** (rise from ocean floor with no continental connection).
**Continental islands:**
- Individual: Newfoundland (Strait of Belle Isle), Malagasy (Mozambique Channel), Sri Lanka (Palk Strait), Tasmania (Bass Strait), Taiwan (Formosa Strait)
- Archipelagos: British Isles, Balearic Islands, Aegean islands
- Festoons/Island arcs: Continuation of mountain ranges — East Indies, Aleutian Islands, Ryukyu Islands, Kurile Islands
**Oceanic islands:**
- Volcanic islands: Built up from ocean floor volcanic cones; e.g. Mauna Loa (Hawaii, 4,169m above sea-level but 5,490m from ocean floor); Azores, Ascension, St. Helena, Madeira, Canary Islands (Atlantic); Mauritius and Reunion (Indian Ocean)
- Coral islands: Very low, just above water; Marshall Islands, Gilbert and Ellice Islands (Pacific); Bermuda (Atlantic); Laccadives and Maldives (Indian Ocean)
**Coral Reefs:**
Reef-building corals are polyps that secrete calcium carbonate. They thrive only under:
1. Water temperature NOT below 20°C (68°F) — limited to tropical/subtropical zones
2. Water depth NOT exceeding 30 fathoms (~55m/180 feet) — for photosynthesis by algae
3. Clear, saline, sediment-free, well-oxygenated water — hence absent near muddy river mouths
4. Absent on western coasts of continents where cold currents upwell
Pacific and Indian Oceans have the most coral reefs. Gulf Stream extends coral range far north of West Indies.
**Three types of coral reef:**
1. **Fringing reef**: Platform close to shore, sometimes separated by shallow lagoon; widest at headlands; absent at stream mouths; ~1 km wide; e.g. common in Red Sea, Indian Ocean
2. **Barrier reef**: Separated from coast by wide, deep channel/lagoon; partially submerged; has navigable gaps; **Great Barrier Reef** (Queensland, Australia): 1,930 km long, channel up to 160 km wide, >60m deep
3. **Atoll**: Ring/oval coral reef enclosing a central lagoon; island/land has sunk (Darwin's theory); e.g. Marshall Islands, Maldives, Laccadives
**Darwin's Subsidence Theory**: Fringing reef → Barrier reef → Atoll as volcanic island subsides. Coral keeps pace with subsidence by growing upward, eventually forming ring around submerged island.
All key facts
›Sri Lanka separated from India by Palk Strait (p.97)
›Tasmania separated from Australia by Bass Strait (p.97)
›Malagasy separated from Africa by Mozambique Channel (p.97)
›Taiwan separated from China by Formosa Strait (p.97)
›Mauna Loa, Hawaii: 4,169m above sea-level; built from ocean floor at 5,490m depth (p.97)
›Coral polyps thrive: water temp >20°C, depth <30 fathoms (55m), clear saline water (p.99)
›Great Barrier Reef: 1,930 km long, up to 160 km wide channel, >60m deep (p.100)
›Coral absent on western coasts of continents (cold upwelling currents) (p.99)
›Gulf Stream extends coral range northward in Atlantic (p.99)
›Pacific and Indian Oceans have most coral reefs (p.99)
›Laccadives and Maldives = coral islands, Indian Ocean (p.98)
›Fringing reef: closest to shore, no deep channel; 1 km wide typically (p.100)
›Atolls are low islands found in tropical oceans, consisting of coral reefs surrounding a central depression, which may be a sea lagoon or enclose fresh, brackish, or highly saline water. (ch12-water-oceans.md)
Water Action Landforms in Deserts
›Few deserts are completely without rain or water. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Annual precipitation in deserts can be small, ranging from 127 to 254 mm (5 to 10 inches), and occurs as irregular showers. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Thunderstorms in deserts produce torrential downpours and flash-floods, which can have devastating effects. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
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While deserts are typically associated with aridity, very few are entirely devoid of rain. Water action plays a significant role in shaping desert landscapes, despite the low and irregular annual precipitation, which typically ranges from 127 to 254 mm (5 to 10 inches). Rain often occurs as torrential thunderstorms and downpours, leading to devastating flash-floods. The scarcity of vegetation in deserts means that the surface soil is unprotected, allowing large quantities of rock wastes to be transported by these sudden torrents.
The erosional work of water includes the cutting of deep gullies and ravines, resulting in "badland topography." Subsequent downpours widen and deepen these features by washing away more soft rocks. Larger dry channels, known as wadis, are deepened by vertical corrasion during cloudbursts and remain dry for most of the time. In places like Algeria, such gorges are termed chebka. Some desert streams, called exotic streams, originate from melting snow in distant mountains outside the desert regions.
Depositional landforms created by water include alluvial cones, fans, or "dry deltas," which form when masses of debris carried by flash-floods are deposited at the base of hills or valley mouths. In arid and semi-arid regions, intermittent streams drain into lower depressions, creating temporary lakes with high salt content that appear glistening white when dry. These lakes and their associated alluvial plains are known as playas, salinas, or salars in the United States and Mexico, and shotts in northern Africa. The floor of such depressions may also feature a bajada, which is a depositional accumulation of alluvial material, and a pediment, an erosional plain at the base of surrounding mountain scarps.
All key facts
›Few deserts are completely without rain or water. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Annual precipitation in deserts can be small, ranging from 127 to 254 mm (5 to 10 inches), and occurs as irregular showers. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Thunderstorms in deserts produce torrential downpours and flash-floods, which can have devastating effects. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›The lack of vegetation in deserts allows large quantities of rock wastes to be transported by flash-floods. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Flash-floods cut deep gullies and ravines, forming "badland topography." — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›When debris masses are deposited at the foot of hills or mouths of valleys, "alluvial cones," "alluvial fans," or "dry deltas" are formed. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Wadis are larger dry channels or valleys in deserts, deepened by vertical corrasion during cloudbursts and dry for most of the time. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›In Algeria, steep-walled gorges carved by water are called chebka. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›"Exotic streams" are desert rivers fed by melting snow from distant mountains outside the deserts. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
Formation of Lakes by Glaciation
›Cirque lakes, or tarns, are formed in circular, armchair-shaped hollows (cirques or corries) left by glaciers in mountain valley heads (p. 82).
›Lakes that occupy glacial troughs are long and deep, known as ribbon lakes (p. 82).
›Red Tarn in the English Lake District is an example of a cirque lake, while Lake Ullswater exemplifies a ribbon lake (p. 82).
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Glaciation is a significant geological process that leads to the formation of various types of lakes. These lakes originate from the erosional and depositional activities of glaciers and ice sheets. Key types include cirque lakes, also known as tarns, which form in the armchair-shaped hollows at the heads of mountain valleys and can develop into long, deep ribbon lakes if they occupy glacial troughs. Kettle lakes are depressions created in outwash plains by the melting of stagnant ice masses, typically irregular, small, and shallow due to the uneven morainic surface. Rock-hollow lakes result from ice-scouring, where the intense abrasive action of valley glaciers or ice sheets scoops out hollows on the land surface.
Beyond erosion, glacial deposition also contributes to lake formation. Lakes can be formed through the morainic damming of valleys, where debris deposited by valley glaciers blocks a valley, causing water to accumulate behind the barrier. Both lateral and terminal moraines are capable of forming such dams. Furthermore, in glaciated lowlands characterized by a drumlin landscape and poor drainage, small lakes can form in the waterlogged depressions created by the deposition of glacial drifts. Finland, for example, is renowned for its abundance of glacial lakes, often referred to as "Suomi – the Land of Lakes."
All key facts
›Cirque lakes, or tarns, are formed in circular, armchair-shaped hollows (cirques or corries) left by glaciers in mountain valley heads (p. 82).
›Lakes that occupy glacial troughs are long and deep, known as ribbon lakes (p. 82).
›Red Tarn in the English Lake District is an example of a cirque lake, while Lake Ullswater exemplifies a ribbon lake (p. 82).
›Kettle lakes are depressions found in outwash plains, created by the melting of stagnant ice masses (p. 82).
›These kettle lakes are irregular in shape, never of significant size or depth, and examples include the meres of Shropshire (England) and the kettle-lakes of Orkney (Scotland) (p. 82).
›Rock-hollow lakes are formed by the process of ice-scouring, where valley glaciers or ice sheets scoop out hollows on the surface (p. 82).
›Finland, also called "Suomi—the Land of Lakes," has over 35,000 glacial lakes, many of which are rock-hollow lakes (p. 82).
›Lakes can form due to morainic damming, where valley glaciers deposit morainic debris across a valley, creating a barrier behind which water accumulates (p. 82).
›Both lateral and terminal moraines can dam valleys, leading to lakes such as Lake Windermere in the English Lake District (p. 83).
›In glaciated lowlands with a predominant drumlin landscape and poor drainage, depressions can become waterlogged due to the deposition of glacial drifts, forming small lakes like those in County Downs, Northern Ireland (p. 83).
›Glacier-formed lakes in the Alps contribute significantly to the tourist industry in Switzerland (p. 86).
Coastal Landforms — Erosion and Deposition by Waves
›Average Atlantic wave pressure: 2,932 kg/sq m in summer; treble in winter (p.88)
›Storm waves: >29,320 kg/sq m pressure (p.88)
›Swash = water rushing up beach; Backwash = retreating water (p.88)
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Coastlines are continuously modified by waves, tides, and currents. Waves are the most powerful agent of marine erosion, and coastal processes are highly dynamic and destructive. Normal ocean waves: 6m high, 120m long (wavelength). On approaching shore, waves slow, crest curls and breaks as **breakers**; water rushing up beach = **swash**; retreating water = **backwash**. Storm waves and tsunami waves can cause far-reaching changes in a short period.
**Marine erosion processes:** Corrasion/Abrasion (rock debris battering cliffs), Attrition (fragments grinding each other), Hydraulic action (compressed air in joints exploding outward), Solvent action (dissolution of limestone coasts).
**Coastal erosion landforms:**
- **Capes and bays**: Hard rocks persist as headlands/capes; soft rocks eroded into bays/coves
- **Cliffs**: Steep rock face adjoining coast; wave-cut notch at base undermines cliff; **wave-cut platform** (gently sloping rocky shelf at base, exposed at low tide) and **wave-cut terrace** (flat or gently sloping platform at the foot of cliffs, covered by rock debris, occurring above average wave height).
- **Cave**: Excavated hole in cliff at zone of weakness due to lashing waves and rock debris; e.g. Flamborough Head, England
- **Arch**: Two caves from opposite sides of headland join (e.g. Durdle Door)
- **Stack**: Roof of arch collapses, leaving isolated rock pillar, or resistant rock masses left as remnants when cliffs retreat
- **Stump**: Stack eroded to low rock exposed only at low tide
- **Blow-hole**: Vertical chimney from cave roof to cliff top through which water/spray jets
**Coastal deposition landforms:**
- **Beach**: Accumulation of sand/shingle/pebbles deposited by waves; formed by swash depositing and backwash transporting. Beaches are temporary features, with sediment from land or wave erosion. Can be sandy or shingle.
- **Spit**: Elongated ridge of sand/shingle extending from headland; can be a barrier bar keyed up to one end of a bay, or attached to headlands/hills. Hooked/recurved end due to refracted waves; e.g. Chesil Beach (Dorset), Dungeness
- **Bar**: Spit that extends completely across a bay; can enclose a lagoon. Includes **off-shore bar** (ridge of sand/shingle parallel to coast in off-shore zone) and **barrier bar** (an off-shore bar exposed due to further sand addition).
- **Tombolo**: Bar connecting an island to mainland; e.g. several Mediterranean examples
- **Sand dune**: Wind-blown sand inland from beach; held by marram grass, forming long ridges parallel to coastline.
- **Lagoon**: Body of water enclosed behind bar/spit/barrier bars. They eventually get filled by sediments to form coastal plains.
- **Wave-built terrace**: Develops in front of a wave-cut terrace in the offshore, with addition of material, after considerable cliff development and retreat.
**Types of coastline:**
- **Drowned (Concordant/Dalmatian)**: Submergence of river valleys → rias; glacial troughs → fiords; ridge-parallel to coast → Dalmatian coast (Adriatic). Also referred to as **high, rocky coasts** where erosion features dominate.
- **Emergent (Discordant)**: Raised beaches; marine platforms now above sea-level. Also referred to as **low, smooth and gently sloping sedimentary coasts** where depositional features dominate.
- **Haff coastline**: Long bars/sandbars separating lagoons (haffe) from sea; e.g. Baltic coast
**Strandflat** (wave-cut platform): Off western Norway, width up to 48 km.
The west coast of India is a high rocky retreating coast, dominated by erosional forms, while the east coast of India is a low sedimentary coast, dominated by depositional forms.
All key facts
›Average Atlantic wave pressure: 2,932 kg/sq m in summer; treble in winter (p.88)
›Storm waves: >29,320 kg/sq m pressure (p.88)
›Swash = water rushing up beach; Backwash = retreating water (p.88)
›Normal ocean wave: 6m high, 120m long (wavelength) (p.88)
›Strandflat, western Norway: wave-cut platform up to 48 km wide (p.89)
›Beachy Head, English Channel: chalk cliff 150m (500 feet) high (p.89)
›Coral reefs absent on western coasts of continents (cold currents) (Ch.11)
›The work of waves as an erosional agent is not controlled by climate, but by their location along the interface of the lithosphere and hydrosphere (coastal region). (ch05-landforms.md)
›Coastal processes are the most dynamic and hence most destructive. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Storm waves and tsunami waves can cause far-reaching changes in a short period of time compared to normal breaking waves. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
Karst and Limestone Landforms
›Karst = term for limestone topography; derived from Karst district of Yugoslavia (p.76)
Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO₃). It is soluble in rainwater mixed with CO₂ (forming weak carbonic acid). A region of extensive limestone with distinctive solutional topography is called a **karst region**, named after the Karst district of Yugoslavia (now Slovenia/Croatia) in the Balkans adjacent to the Adriatic Sea, where such features are best developed. Dolomite = limestone with magnesium also present. Chalk = very pure, soft form of limestone.
**Karst characteristics:**
- General absence of surface drainage (most water goes underground)
- Dry surface valleys
- Prominent jointed/fractured limestone surface
**Surface karst features:**
- **Limestone pavement**: Flat bare rock; enlarged joints called **grikes**; rectangular blocks called **clints**
- **Swallow holes/Sink holes**: Small depressions where rainwater sinks into rock; e.g. Gaping Ghyll, Yorkshire. Sinkholes can vary in area from a few square meters to a hectare, and in depth from less than half a meter to thirty meters or more.
- **Doline**: A single enlarged swallow hole (also called dolina). The term doline is sometimes used to refer to collapse sinks, where the bottom of a sinkhole forms a cave roof that collapses.
- **Uvala**: Several dolinas merged by subsidence; also called valley sinks.
- **Polje**: Very large depression (up to 100 sq km) partly due to faulting; e.g. in Yugoslavia; floors can be temporary lakes seasonally
- **Lapies**: Extremely irregular surface with a maze of points, grooves, and ridges formed due to differential solution activity along parallel to sub-parallel joints.
**Underground karst features:**
- **Caves and caverns**: Carved by underground streams along joints/bedding planes. Prominent where limestones are dense, massive, and occur as thick beds, or where alternating beds of rocks (shales, sandstones, quartzites) are present.
- **Stalactites**: Downward-hanging calcium carbonate pinnacles from cave roof, broad at their bases and tapering towards the free ends.
- **Stalagmites**: Upward-growing calcium carbonate deposits from cave floor, forming due to dripping water from stalactites or the surface. They can take the shape of a column, a disc, or have a smooth, rounded bulging end or a miniature crater-like depression.
- **Pillar/Column**: Stalactite and stalagmite joined together.
- **Gorge**: Formed when roof of underground tunnel collapses (e.g. Cheddar Gorge)
- **Resurgence (Vauclusian spring)**: Underground river re-emerges when limestone meets impermeable rock
- **Tunnels**: Caves having openings at both ends.
**Notable limestone caves:** Batu Caves (Kuala Lumpur), Mammoth Caves (Kentucky), Carlsbad Cave (New Mexico), Postojna Caves (Yugoslavia).
**Major limestone regions:** NW Yugoslavia (Karst district), Causses (S France), Pennines (Britain), Kentucky (USA), Yucatan Peninsula (Mexico), Cockpit Country (Jamaica).
**Chalk landforms:** Less dramatic than limestone; dry valleys (coombes); low rounded hills ('downs' in S England, N France); short turf pasture.
All key facts
›Karst = term for limestone topography; derived from Karst district of Yugoslavia (p.76)
›Uvala = merged dolinas; Polje can be up to 100 sq km (Yugoslavia) (p.78)
›Mammoth Caves, Kentucky; Carlsbad Cave, New Mexico; Batu Caves, KL (p.79)
›Karst regions are typically poor in agriculture due to lack of surface water and thin soils (p.79)
›Lead ore occurs in limestone regions (p.79)
›Chalk downs = low rounded hills in S England and N France (p.79)
›Karst topography is named after the Karst region in the Balkans adjacent to the Adriatic Sea (NCERT ch06, p.52)
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Wind Erosional Landforms (Deserts)
›Wind erosional landforms are a result of the combined processes of abrasion, deflation, and attrition. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Abrasion** involves sand-blasting of rock surfaces by wind-borne particles, causing scratching, polishing, and wearing away, primarily effective at or near the base of rocks. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Deflation** is the lifting and blowing away of loose materials, leading to the lowering of the land surface and the formation of deflation hollows. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
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Wind erosional landforms in deserts emerge from the combined processes of abrasion, deflation, and attrition, which are particularly effective in arid regions due to sparse vegetation and moisture. Abrasion involves wind-blown sand particles scratching, polishing, and wearing away rock surfaces, being most effective at the base of rocks. Deflation is the lifting and blowing away of loose materials, leading to the lowering of land surface and formation of depressions. Attrition refers to wind-borne particles colliding and wearing each other down, reducing their size and rounding them into shapes like millet seed sand.
These processes sculpt various characteristic landforms. Rock pedestals, also known as mushroom rocks or gour, form when winds abrade softer layers of projecting rock masses, especially near the base, creating an undercut mushroom shape. Zeugen are tabular masses with a resistant surface layer over softer rocks, carved into a "ridge and furrow" landscape by wind abrasion, with hard rocks forming ridges. Yardangs are similar but feature vertical bands of hard and soft rocks aligned with prevailing winds, where softer bands are excavated into corridors and hard rocks form steep-sided ridges. Mesas are flat, table-like landmasses with a resistant horizontal top layer and steep sides, which can be reduced in area by denudation to form isolated flat-topped hills called buttes. Inselbergs are isolated residual hills with steep slopes and rounded tops, often composed of granite or gneiss. Ventifacts (or dreikanter) are pebbles faceted and polished by sand-blasting, often with multiple flattened surfaces and sharp edges. Deflation hollows are depressions formed by winds blowing away unconsolidated materials, sometimes reaching the water-table to create oases or swamps.
All key facts
›Wind erosional landforms are a result of the combined processes of abrasion, deflation, and attrition. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Abrasion** involves sand-blasting of rock surfaces by wind-borne particles, causing scratching, polishing, and wearing away, primarily effective at or near the base of rocks. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Deflation** is the lifting and blowing away of loose materials, leading to the lowering of the land surface and the formation of deflation hollows. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Attrition** is the process where wind-borne particles collide and wear each other away, reducing their size and rounding them. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Rock Pedestals (Mushroom Rocks/Gour)**: Formed by differential wind abrasion on projecting rock masses, wearing back softer layers and undercutting near the base due to greater friction. Examples include 'gour' in the Sahara. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Zeugen**: Tabular masses consisting of a resistant surface rock layer over a softer layer, sculpted by wind abrasion into a "ridge and furrow" landscape. They can stand 3 to 30 meters (10 to 100 feet) above sunken furrows. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Yardangs**: Similar to zeugen but with vertical bands of hard and soft rocks aligned with prevailing winds. Wind abrasion excavates softer bands into long corridors, leaving steep-sided ridges of hard rock. Commonly found in the Atacama Desert, Chile, and Central Asia. They can rise to 8-15 meters (25-50 feet). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
Lakes — Formation, Types, and Distribution
›Caspian Sea: 1,223 km long, 980m deep, 373,230 sq km — world's largest lake (p.82)
›Lake Tanganyika: 1,430m deep — world's deepest lake (East African Rift) (p.82)
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Lakes are bodies of water occupying hollows of the land surface. They vary enormously in size, depth, mode of origin, and water chemistry. Lakes are temporary features in geological time — eventually eliminated by silting up or draining. Salt lakes form in regions of internal drainage where evaporation > inflow.
**Major lake types by origin:**
**1. Earth Movement Lakes:**
- **Tectonic lakes**: Formed by warping/sagging/fracturing of crust; e.g. Lake Titicaca (highest lake — 3,810m, Andes); Caspian Sea (largest lake — 373,230 sq km)
- **Rift valley lakes**: Formed by faulting; deep, narrow, elongated; floors often below sea-level; East African Rift Valley lakes: Tanganyika (1,430m deep — world's deepest lake), Malawi, Rudolf, Edward, Albert; Dead Sea (392m below sea-level — world's lowest point)
**2. Glacial Lakes:**
- **Cirque lakes/Tarns**: In over-deepened corrie floors; e.g. Red Tarn, English Lake District
- **Ribbon lakes**: Long, narrow lakes in glacial troughs; e.g. Lake Ullswater
- **Kettle lakes**: In outwash plain depressions from melted stagnant ice; e.g. meres of Shropshire
- **Rock-hollow lakes**: Ice-scoured hollows; abundant in Finland (35,000+ lakes)
- **Moraine-dammed lakes**: Terminal/lateral moraine dam; e.g. Lake Windermere, Lake District
- **Drumlin landscape lakes**: Depressions between drumlins; e.g. County Down, N Ireland
**3. Volcanic Lakes:**
- **Crater/Caldera lakes**: In dormant/extinct volcanic craters; e.g. Crater Lake, Oregon (USA); Lake Toba, N Sumatra; Lake Avernus, near Naples
- **Lava-blocked lakes**: Lava flow dams valley; e.g. Sea of Galilee (Jordan Valley, lava-blocked)
- **Subsidence lakes**: Hollow lava flow collapses; e.g. Myvatn, Iceland
**4. Erosional Lakes:**
- **Karst lakes**: Solution hollows in limestone; e.g. Lac de Chaillexon, Jura; Lake Scutari, Yugoslavia
- **Wind-deflated lakes**: Deflation hollows reach groundwater; e.g. Qattara Depression, Egypt; Great Basin, Utah — become salt lakes/playas
**5. Depositional Lakes:**
- **Oxbow lakes**: Cut-off meander loops in river's lower course
- **Floodplain lakes**: Back-swamps and waterlogged areas of floodplain
- **Delta lakes**: In deltaic regions; e.g. Lake Chilika (India)
- **Coastal lakes**: Bar/lagoon enclosure; e.g. Chilika (salty lagoon), Chilka Lake
**Salinity facts:** Dead Sea: 250 parts per thousand; Great Salt Lake, Utah: 220 ppt; Black Sea (many large rivers): only 17 ppt; Normal ocean: ~35 ppt.
All key facts
›Caspian Sea: 1,223 km long, 980m deep, 373,230 sq km — world's largest lake (p.82)
›Finland: 35,000+ glacial lakes — 10% of country's surface (p.83)
›Crater Lake, Oregon = caldera lake (not true crater) (p.83)
›Lake Toba, N Sumatra = crater lake (p.83)
›Sea of Galilee = lava-blocked lake on Jordan Valley (p.84)
›Dead Sea salinity: 250 ppt; Great Salt Lake: 220 ppt; Black Sea: 17 ppt (p.82)
›Oxbow lake = horseshoe-shaped cut-off meander (p.84)
›Playas = salt lakes in deserts (common feature) (p.82)
›Lake Windermere, Lake District = moraine-dammed lake (p.83)
›Red Tarn, English Lake District = cirque/tarn lake (p.83)
›Most lakes in the world are freshwater lakes fed by rivers and with out-flowing streams. (p.82)
Glacial Landforms — Erosion and Deposition by Ice
›Ice Age covered >31 million sq km of northern hemisphere (p.58)
›Greenland ice cap: 1,872,000 sq km (720,000 sq miles) (p.58)
›Antarctica ice cap: >13 million sq km (5 million sq miles) (p.58)
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During the Pleistocene Ice Ages (~30,000 years ago), ice covered >31 million sq km of the northern hemisphere. Today major ice caps remain in Greenland (1.87 million sq km) and Antarctica (>13 million sq km). Glaciers form when snow accumulates, compresses into névé/firn (granular ice), and flows downhill under gravity. Masses of ice moving as sheets over land (continental or piedmont glaciers) or as linear flows down mountain slopes in broad trough-like valleys (mountain and valley glaciers) are called glaciers.
Glaciers erode by two processes: **Plucking** (freezing and tearing away blocks) and **Abrasion** (scratching/scouring with embedded debris, producing striation marks and rock flour). Erosion by glaciers is tremendous due to friction caused by the sheer weight of the ice, which can reduce high mountains into low hills and plains.
**Highland glacial erosion features:**
- **Corrie/Cirque/Cwm**: Armchair-shaped depression where firn accumulates; steep horseshoe-shaped basin with rocky lip; fills with water to form a tarn
- **Arête**: Knife-edge ridge between two corries cutting back from opposite sides (e.g. Striding Edge, Helvellyn, UK)
- **Pyramidal peak/Horn**: Formed where 3+ corries cut back together (e.g. Matterhorn, Switzerland)
- **Bergschrund**: Deep vertical crack at head of glacier in summer
- **U-shaped glacial trough**: Wide, flat floor, steep sides; interlocking spurs blunted to truncated spurs; long/ribbon lakes form in overdeepened sections (e.g. Loch Ness, Lake Ullswater)
- **Hanging valley**: Tributary valley 'hangs' above main valley after ice melts; stream plunges as waterfall (good for HEP)
- **Rock basins and rock steps**: Unequal excavation creates basins later filled by lakes
**Moraines:** Lateral (sides), Medial (two glaciers join), Ground (beneath glacier), Terminal/End (at snout), Recessional (formed as ice retreats by stages).
**Highland glaciation lowland features:**
- **Roche moutonnée**: Resistant rock hummock; upstream side smooth (abrasion), downstream side rough and steep (plucking)
- **Crag and tail**: Resistant rock crag protects lee side from erosion; tail of softer rock behind (e.g. Edinburgh Castle Rock)
- **Drumlins**: Streamlined egg-shaped hills of boulder clay; formed subglacially; long axis parallel to ice movement
- **Eskers**: Long, winding ridges of sand and gravel deposited by meltwater streams beneath glacier
- **Kames**: Mounds of sand and gravel deposited by meltwater
- **Outwash plain**: Sandy/gravelly plain beyond terminal moraine, deposited by meltwater
- **Till plain/Boulder clay**: Mixed boulders and clay deposited by glacier; fertile farmland (e.g. US Midwest, East Anglia)
- **Fiord**: Drowned U-shaped valley; typical of Norwegian and south Chilean coasts
All key facts
›Ice Age covered >31 million sq km of northern hemisphere (p.58)
›Greenland ice cap: 1,872,000 sq km (720,000 sq miles) (p.58)
›Antarctica ice cap: >13 million sq km (5 million sq miles) (p.58)
›Striding Edge, Helvellyn = classic arête in Britain (p.61)
›Fiords most typical of Norwegian and south Chilean coasts (p.62)
Formation of Lakes by Earth Movements
›Lakes formed by earth movements include [[Tectonic Lakes]] and [[Rift Valley Lakes]]. (ch09-lakes.md)
›**Tectonic lakes** are formed by tectonic depressions caused by the warping, sagging, bending, and fracturing of the earth's crust. (ch09-lakes.md)
›These tectonic depressions result in lakes of immense sizes and depths. (ch09-lakes.md)
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Lakes formed by earth movements result from the deformation of the Earth's crust, creating depressions that collect water. This category primarily includes tectonic lakes and rift valley lakes.
Tectonic lakes originate from extensive depressions formed by processes such as warping, sagging, bending, and fracturing of the earth's crust. These geological activities lead to large and deep basins where water accumulates. Notable examples of tectonic lakes include Lake Titicaca, which is situated in a high intermont plateau, and the Caspian Sea, recognized as the world's largest lake.
Rift valley lakes are a specific type of lake formed by faulting. A rift valley is created when a block of land sinks between two parallel faults, resulting in a deep, narrow, and elongated trough. Water then gathers in these troughs, and their floors often lie below sea-level. The East African Rift Valley is a prominent example of such a formation, containing several significant lakes like Lake Tanganyika (one of the world's deepest) and the Dead Sea (the world's lowest lake).
All key facts
›Lakes formed by earth movements include [[Tectonic Lakes]] and [[Rift Valley Lakes]]. (ch09-lakes.md)
›**Tectonic lakes** are formed by tectonic depressions caused by the warping, sagging, bending, and fracturing of the earth's crust. (ch09-lakes.md)
›These tectonic depressions result in lakes of immense sizes and depths. (ch09-lakes.md)
›Examples of tectonic lakes include Lake Titicaca (highest lake in the world, 3,810 metres above sea-level) and the Caspian Sea (largest lake, nearly 5 times larger than Lake Superior). (ch09-lakes.md)
›**Rift valley lakes** are formed due to faulting, where a rift valley is created by the sinking of land between two parallel faults. (ch09-lakes.md)
›Rift valleys are characterized by being deep, narrow, and elongated. (ch09-lakes.md)
›Water collects in these troughs, and their floors are often below sea-level. (ch09-lakes.md)
›The East African Rift Valley is a key example, extending over 4,800 km and running through countries like Zambia, Malawi, Tanzania, Kenya, and Ethiopia, and along the Red Sea to Israel and Jordan. (ch09-lakes.md)
›Lakes within the East African Rift Valley include Lake Tanganyika (the world's deepest lake at 1,430 m deep), Lake Malawi, Lake Rudolf, Lake Edward, Lake Albert, and the Dead Sea (the world's lowest lake at 392 metres below mean sea-level). (ch09-lakes.md)
Earth's Structure, Rock Types, and Major Landforms
›Crust thickness: 5–6 km under oceans; up to 48 km under continents (p.17)
›SIAL floats on SIMA because it is lighter (density 2.7 vs 3.0) (p.17)
›Mantle is ~2,900 km thick, rich in olivine (p.17)
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The Earth consists of concentric layers. The outermost is the **lithosphere (crust)** divided into **SIAL** (upper continental crust — silica + alumina, density 2.7) and **SIMA** (lower basaltic crust — silica + iron + magnesium, density 3.0). Beneath the crust is the **mantle (mesosphere)** ~2,900 km thick, rich in olivine. The innermost is the **core (barysphere)** — radius 3,476 km, composed mainly of iron-nickel (**NIFE**), temperature ~1,927°C. The innermost core is solid/crystalline despite high temperature due to extreme pressure.
**Three classes of rocks:**
1. **Igneous rocks**: Formed by cooling of magma. Plutonic (intrusive, e.g. granite) cool slowly and have large crystals. Volcanic (extrusive, e.g. basalt) cool rapidly with small crystals. Acid igneous rocks (high silica, lighter) vs. Basic igneous rocks (more iron/aluminium, darker, denser).
2. **Sedimentary rocks**: Formed from accumulated sediments, characterised by distinct strata. Contain fossils. Types: Mechanically formed (sandstone, conglomerate, shale), Organically formed (limestone, chalk, coal), Chemically formed (rock salt, gypsum).
3. **Metamorphic rocks**: Existing rocks altered by heat and pressure. Clay → slate; limestone → marble; sandstone → quartzite; granite → gneiss; shale → schist; coal → graphite.
**Four types of mountains:** Fold mountains (most widespread — Himalayas, Andes, Alps, Rockies), Block mountains/Horsts (e.g. Vosges, Black Forest), Volcanic mountains (e.g. Mt. Fuji, Mt. Etna), Residual mountains (e.g. Mt. Monadnock, Scottish Highlands).
**Orogenic events:** Caledonian (~320 mya — Scotland, Scandinavia); Hercynian (~240 mya — Ural, Pennines, Appalachians); Alpine (~30 mya — Alps, Himalayas, Andes, Rockies — still highest because most recent).
All key facts
›Crust thickness: 5–6 km under oceans; up to 48 km under continents (p.17)
›SIAL floats on SIMA because it is lighter (density 2.7 vs 3.0) (p.17)
›Mantle is ~2,900 km thick, rich in olivine (p.17)
›Core radius 3,476 km, mainly iron-nickel (NIFE), inner core is solid (p.17)
›East African Rift Valley: 4,828 km long, stretches from East Africa through Red Sea to Syria (p.22)
›Himalayan examples of young fold mountains — most recently formed (~30 mya), hence tallest (p.20)
›Anticlines = upfolds; Synclines = downfolds in fold mountains (p.21)
›Nappe = overriding portion of a thrust/overthrust fold (p.21)
›Horst = block mountain; Graben = rift valley (p.22)
›Tibetan Plateau = intermont plateau between Himalayas and Kunlun (p.23)
›Bolivian Plateau = intermont plateau between two Andes ranges (p.23)
›Columbia-Snake Plateau = volcanic/lava plateau, area almost twice Malaysia (p.23)
›Deccan Plateau = tectonic plateau; also has volcanic portion (NW part) (p.23)
›
Ice Caps
›Ice caps are found primarily north of the Arctic Circle in the Northern Hemisphere. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
›They are confined to Greenland and the highlands of high-latitude regions. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
›The ground in ice cap regions is permanently snow-covered. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
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Ice caps represent regions of permanently snow-covered ground, characterized by thick layers of ice. In the Northern Hemisphere, they are primarily found north of the Arctic Circle, specifically confined to Greenland and the highlands of high-latitude areas. In contrast to lowlands which may become ice-free for a few months and support tundra vegetation, ice caps remain permanently frozen. The Southern Hemisphere hosts the most extensive single stretch of ice cap on the continent of Antarctica, where the permanent ice layers can reach depths of up to 3,000 metres. These massive ice bodies are associated with large anticyclones, from which winds may blow.
All key facts
›Ice caps are found primarily north of the Arctic Circle in the Northern Hemisphere. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
›They are confined to Greenland and the highlands of high-latitude regions. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
›The ground in ice cap regions is permanently snow-covered. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
›Antarctica is the greatest single stretch of ice cap in the Southern Hemisphere. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
›The layers of permanent ice in Antarctica can be as thick as 3,000 metres (10,000 feet). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
›Large anticyclones can develop over ice caps. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch25-the-arctic-or-polar-climate.md
Cyclones, Anticyclones, and Weather Systems
›Tropical cyclones derive energy from warm ocean water (latent heat of condensation)
›The energy intensifying a tropical storm specifically comes from the condensation process in towering cumulonimbus clouds surrounding the storm's centre — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›The eye of a cyclone is calm; maximum winds and rainfall in the eye wall
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A cyclone is a large-scale circulation of winds around a centre of low atmospheric pressure. An anticyclone is a circulation around a centre of high pressure. The two differ in rotation direction, wind behaviour, and associated weather.
**Tropical Cyclones:**
Tropical cyclones form over warm tropical oceans (sea surface temperature above 27°C). They derive energy from the latent heat released as moist warm air rises and condenses. Key characteristics:
- Winds spiral inward and upward
- A calm "eye" at the centre surrounded by the most intense winds and rainfall in the "eye wall"
- Rotate anti-clockwise in Northern Hemisphere, clockwise in Southern Hemisphere
- Called hurricanes (Atlantic), typhoons (Pacific), cyclones (Indian Ocean/Bay of Bengal)
- Dissipate when they move over land or cool water (lose their energy source)
**Temperate Cyclones (Extra-tropical):**
Also called depressions or mid-latitude cyclones. They form along the polar front where warm and cold air masses meet. Unlike tropical cyclones, they have frontal systems (warm front, cold front) and do not have a calm eye. They move generally west to east in the westerlies belt.
**Anticyclones:**
Regions of high pressure with outward-spiralling winds. Associated with clear, settled weather. In Northern Hemisphere, winds spiral clockwise; Southern Hemisphere, anti-clockwise.
The Bay of Bengal is more cyclone-prone than the Arabian Sea due to:
- Higher sea surface temperatures
- Enclosed shape funnelling storm energy
- Warmer, more humid conditions throughout the year
All key facts
›Tropical cyclones derive energy from warm ocean water (latent heat of condensation)
›The energy intensifying a tropical storm specifically comes from the condensation process in towering cumulonimbus clouds surrounding the storm's centre — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›The eye of a cyclone is calm; maximum winds and rainfall in the eye wall
›The eye of a tropical cyclone is a region of calm with subsiding air — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›In the eye wall of a tropical cyclone, there is a strong spiralling ascent of air to greater height, reaching the tropopause, and winds can reach up to 250 km per hour with torrential rain — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Tropical cyclones rotate anti-clockwise in N. Hemisphere (due to Coriolis effect)
›Tropical cyclones rotate clockwise in the Southern Hemisphere — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Anticyclones in the Northern Hemisphere have clockwise wind circulation, while in the Southern Hemisphere, they have anti-clockwise circulation — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Tropical cyclones cannot form within 5° of the equator (Coriolis effect too weak)
›At the equator, the Coriolis force is zero, causing low pressure to fill instead of intensifying, which prevents tropical cyclone formation — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
Atmospheric Circulation — Pressure Belts and Wind Systems
›Pressure belts are not always continuous; they are interrupted by land masses (especially in Northern Hemisphere)
›The ITCZ shifts north in summer and south in winter, following the apparent movement of the Sun — this is the basis of the monsoon
›Trade winds are the most consistent planetary winds
+ 36 facts · tap to read
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Atmospheric circulation is driven by the unequal heating of the Earth's surface. This creates zones of high and low pressure that drive the global wind systems.
**Pressure Belts (from equator to poles):**
1. **Equatorial Low Pressure Belt (ITCZ — Inter-Tropical Convergence Zone)**: Around 0°, intense solar heating causes air to rise, creating a low-pressure belt. Calm conditions and heavy rainfall prevail. Also called the Doldrums.
2. **Sub-Tropical High Pressure Belts**: Around 30° N and S. Descending air creates high pressure, resulting in hot deserts on western margins of continents (Sahara, Arabian, Australian deserts). Also called the Horse Latitudes.
3. **Sub-Polar Low Pressure Belts**: Around 60° N and S. Convergence of polar and sub-tropical air masses creates low pressure.
4. **Polar High Pressure Belts**: At the poles, cold air sinks, creating high pressure.
**Planetary Wind Systems:**
- **Trade Winds**: Blow from sub-tropical highs to equatorial lows; northeast trades (N. Hemisphere), southeast trades (S. Hemisphere). Consistent and reliable; used by early sailors.
- **Westerlies**: Blow from sub-tropical highs toward sub-polar lows; from southwest in N. Hemisphere, northwest in S. Hemisphere. Bring rainfall to western coasts of continents in temperate zones.
- **Polar Easterlies**: Blow from polar highs toward sub-polar lows.
The Coriolis force deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, creating the circular patterns observed in pressure systems.
All key facts
›Pressure belts are not always continuous; they are interrupted by land masses (especially in Northern Hemisphere)
›The ITCZ shifts north in summer and south in winter, following the apparent movement of the Sun — this is the basis of the monsoon
›Trade winds are the most consistent planetary winds
›Westerlies are responsible for weather systems (depressions) that move west to east in temperate zones
›The Ferrel Cell circulates between 30° and 60°; Hadley Cell between equator and 30°; Polar Cell between 60° and poles
›Jet streams are fast-moving upper air currents at the tropopause; the sub-tropical jet stream influences Indian monsoon
›The term Doldrums comes from sailors being stranded in the calm equatorial belt
›Atmospheric pressure is the weight of a column of air in a unit area from mean sea level to the top of the atmosphere, expressed in millibars (mb).
›At sea level, the average atmospheric pressure is 1,013.2 millibars.
›Air pressure is measured using a mercury barometer or an aneroid barometer.
›Pressure decreases rapidly with height in the lower atmosphere, approximately 1 mb for each 10 m increase in elevation.
›Isobars are lines connecting places that have equal pressure, used to study horizontal pressure distribution after reduction to sea level.
›Rills develop into gullies, which deepen, widen, lengthen, and unite to form a network of valleys. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A peneplain is a lowland of faint relief with some low resistant remnants called monadnocks, forming as a result of stream erosion. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›**Youth Stage:** Streams are few with poor integration, showing shallow V-shaped valleys with no or very narrow floodplains. Stream divides are broad and flat with marshes, swamps, and lakes. Waterfalls and rapids may exist. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›**Mature Stage:** Streams are plenty with good integration. Valleys are still V-shaped but deep, with wider floodplains where meanders are confined. Stream divides turn sharp, and waterfalls and rapids disappear. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›**Old Stage:** Smaller tributaries are few with gentle gradients. Streams meander freely over vast floodplains showing natural levees and oxbow lakes. Divides are broad and flat with lakes, swamps, and marshes. Most of the landscape is at or slightly above sea level. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A gorge is a deep valley with very steep to straight sides, almost equal in width at its top and bottom, commonly forming in hard rocks. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A canyon is characterised by steep step-like side slopes, wider at its top than its bottom, commonly forming in horizontal bedded sedimentary rocks. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Potholes are circular depressions on rocky beds of hill-streams formed by stream erosion aided by the abrasion of rock fragments. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Plunge pools are large, deep holes at the base of waterfalls formed by the sheer impact of water and rotation of boulders. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Incised or entrenched meanders are very deep and wide meanders cut in hard rocks, found in streams flowing rapidly over steep gradients. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›River terraces are surfaces marking old valley floor or floodplain levels, resulting from vertical erosion by the stream into its own depositional floodplain. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Alluvial fans are formed when streams from higher levels break into foot slope plains of low gradient, dumping coarse load as a cone-shaped deposit. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Alluvial fans in humid areas are low cones with gentle slopes, while in arid/semi-arid climates, they appear as high cones with steep slopes. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Deltas are formed when the load carried by rivers is dumped and spread into the sea; delta deposits are very well sorted with clear stratification. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›As a delta grows, the river distributaries continue to increase in length. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A floodplain is a major landform of river deposition. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A river bed made of river deposits is the active floodplain; the floodplain above the bank is the inactive floodplain. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›The flood plains in a delta are called delta plains. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Natural levees are low, linear, parallel ridges of coarse deposits along the banks of large rivers. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Point bars (meander bars) are sediments deposited in a linear fashion on the concave side of meanders of large rivers. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Meander is not a landform but only a type of channel pattern. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Meanders are caused by (i) lateral working on banks due to gentle gradients; (ii) unconsolidated alluvial deposits; (iii) Coriolis force. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›In meanders of large rivers, there is active deposition along the convex bank and unde
Great Dust Bowl, USA: large-scale deflation after natural vegetation stripped for farming (p.71)
›Wadis = steep-sided, often dry valleys in mountain deserts (p.68)
›Wind erosion includes 'impact', which is the sheer force of momentum occurring when sand is blown into or against a rock surface, similar to sand-blasting. (p.59)
›Many desert features are formed by mass wasting and running water (as sheet floods), in addition to wind. (p.59)
›Though rain is scarce in deserts, it comes torrentially in short periods, and combined with rapid rock decay from drastic diurnal temperature changes, helps remove weathered material easily. (p.59)
›Wind primarily moves fine materials, while general mass erosion in deserts is mainly accomplished through sheet floods or sheet wash. (p.59)
›Pediments are gently inclined rocky floors found close to the foot of mountains, formed by a combination of lateral erosion by streams and sheet flooding. (p.59)
›The erosion method where steep wash slopes and free faces retreat backwards is termed 'parallel retreat of slopes' or 'backwasting'. (p.60)
›Pediplains are low, featureless plains formed from the reduction of mountains (leaving inselbergs) as pediments extend backwards through parallel retreat of slopes. (p.60)
›Playas are shallow, temporary water bodies that form in nearly level plains at the center of desert basins, retaining water for short durations due to evaporation and often containing salt deposits. (p.60)
›A playa plain covered by salts is called an 'alkali flat'. (p.60)
›Desert caves can form when shallow depressions called 'blow outs', created by the impact and abrasion of wind-borne sand, deepen and widen. (p.60)
›Mushroom, table, and pedestal rocks are remnants of resistant rocks, beautifully polished by wind deflation and abrasion, with broad, rounded caps and slender stalks (mushroom shape), or broad table-like tops, or standing out as pedestals. (p.60)
›Parabolic dunes are reversed barchans, forming when sandy surfaces are partially covered with vegetation, with the wind direction remaining constant. (p.61)
›Seif dunes are similar to barchans but have only one wing or point, which can grow very long and high, typically due to a shift in wind conditions. (p.61)
›Longitudinal dunes form when the supply of sand is poor and the wind direction is constant, appearing as long ridges of considerable length but low in height. (p.61)
›Most deserts are tropical hot deserts or 'Trade Wind deserts', bathed by cold currents that produce a desiccating effect. (p.67)
›Mid-latitude deserts (e.g., Gobi, Turkestan) are characterized by extremes of temperatures. (p.68)
›In Libya and Egypt, stony deserts (reg) are specifically called serir. (p.68)
›In Turkestan, sandy deserts (erg) are also known as koum. (p.68)
›The term 'badlands' was first applied to an arid area in South Dakota, U.S.A., due to severe erosion by occasional rain-storms into gullies and ravines. (p.68)
›The Painted Desert of Arizona, south-east of the Grand Canyon, is an example of badlands. (p.68)
›In mountain deserts, the action of frost carves out sharp, irregular edges on steep slopes cut by wadis. (p.68)
›The Ahaggar Mountains and the Tibesti Mountains in the Sahara Desert are examples of mountain deserts. (p.68)
›Aridity is chiefly caused by insufficient rainfall (often less than 127 mm/5 inches) occurring irregularly, coupled with very high average temperatures (31°C/87°F) and a rapid rate of evaporation. (p.68)
›Weathering (mechanical and chemical) is the most potent factor in reducing rocks to sand in arid regions. (p.69)
›Exfoliation is a mechanical weathering process where the hot outer surface of a rock peels off in successive thin layers from the cooler inner rocks, resembling onion-peeling. (p.69)
›Angular rock debris, or screes, accumulates at the foot of upstanding rocks due to exfoliation and successive freezing and expansion of water in cracks. (p.69)
›Wind erosion is more efficient in arid regions than humid ones because there is little vegetation or moisture to bind loose surface materials. (p.69)
›Wind abrasion is most effective at or near the base of rocks, where the amount of material the wind carries is greatest. (p.69)
›Attrition occurs when wind-borne particles collide and wear each other away, reducing their size and rounding them into 'millet seed sand'. (p.69)
›Mushroom rocks (or gour in the Sahara) are formed by the undercutting effect of winds near their bases where friction is greatest. (p.69)
›Zeugen are tabular masses of soft rock beneath resistant rock, sculpted by wind abrasion into a 'ridge and furrow' landscape, with ridges standing 3 to 30 meters (10 to 100 feet) above sunken furrows. (p.69-70)
›Yardangs consist of hard and soft rocks in vertical bands aligned with prevailing winds, where softer bands are excavated into corridors separating steep-sided ridges; they are best developed in Central Asia, rising 8-15 meters (25-50 feet). (p.70)
›Mesa, a Spanish word mea
›
Himalayas have NO active volcanoes — despite being fold mountains (p.33)
›Geysers confined mainly to: Iceland, Rotorua (New Zealand), Yellowstone (USA) (p.33)
›70% of earthquakes in Circum-Pacific belt; 20% in Mediterranean-Himalayan belt (p.34)
›The Earth's radius is approximately 6,378 km. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.18)
›Gold mines in South Africa are as deep as 3-4 km, beyond which it's too hot for exploration. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.18)
›The deepest drill, at Kola in the Arctic Ocean, has reached a depth of 12 km. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.18)
›Magma erupted onto the surface during volcanic eruptions is available for laboratory analysis. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.18)
›Temperature, pressure, and density of material increase with increasing depth from the Earth's surface. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›Meteors, solid bodies developed from materials similar to Earth, provide indirect information about Earth's interior. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›Gravitation force (g) is greater near the poles and less at the equator due to differing distances from the Earth's centre. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›Gravity anomalies (differences from expected gravity values) provide information about the uneven distribution of mass in the Earth's crust. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›Magnetic surveys provide information about the distribution of magnetic materials in the crustal portion. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›A fault is a sharp break in the crustal rocks along which energy is released during an earthquake. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›The point where earthquake energy is released is called the focus or hypocentre. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›The epicentre is the point on the surface directly above the focus, and it is the first to experience earthquake waves. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›All natural earthquakes take place in the lithosphere, which refers to the portion of depth up to 200 km from the surface. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›A seismograph is an instrument that records earthquake waves reaching the surface. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›Earthquake waves are basically of two types: body waves (P and S-waves) and surface waves. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›Body waves are generated at the focus and travel in all directions through the Earth's body. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.19)
›P-waves (primary waves) move faster, are the first to arrive at the surface, are similar to sound waves, and travel through gaseous, liquid, and solid materials. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.20)
›S-waves (secondary waves) arrive after P-waves and can travel only through solid materials. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.20)
›Surface waves are the last to be reported on a seismograph and are considered the most destructive, causing displacement of rocks and structural collapse. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.20)
›P-waves vibrate parallel to the direction of wave propagation, creating density differences (stretching and squeezing). (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.20)
›S-waves vibrate perpendicular to the direction of propagation, creating troughs and crests. (NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md, p.20)
›An earthquake shadow zone is an area where earthquake waves are not reported by seismographs. (NCERT Class 11 — India:
›A better understanding of the physical environment is essential for sustainable development due to ecological imbalances from resource utilization.
›
The Bay of Bengal shows a low salinity trend due to river water influx.
›The Arabian Sea shows higher salinity due to high evaporation and low influx of fresh water.
›The average salinity of the Atlantic Ocean is around 36 o/oo, with the highest salinity (37 o/oo) observed between 20° N and 30° N and 20° W - 60° W.
›In the Pacific Ocean, salinity decreases from 35 o/oo to 31 o/oo on the western parts of the northern hemisphere due to the influx of melted water from the Arctic region, and decreases to 33 o/oo after 15°- 20° S.
›Wind influences salinity by transferring water to other areas.
›Salinity at depth is very much fixed, as water is not lost or salt is added.
›Increasing salinity of seawater causes its density to increase, leading to high salinity seawater sinking below lower salinity water and causing stratification.
›Spring tides occur at new moon and full moon (Sun-Moon-Earth alignment)
›Neap tides occur at first and third quarter moons (right angle alignment)
›Tides are caused by the gravitational attraction of the sun and the moon, and also by centrifugal force, which acts to counterbalance gravity. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›The highest tides in the world occur in the Bay of Fundy in Nova Scotia, Canada, with a tidal bulge of 15-16 m. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Semidiurnal tide is the most common tidal pattern, featuring two high tides and two low tides each day, with successive high or low tides being approximately of the same height. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Diurnal tide features only one high tide and one low tide during each day, with successive high and low tides being approximately of the same height. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Mixed tides have variations in height and generally occur along the west coast of North America and on many islands of the Pacific Ocean. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›When the moon's orbit is closest to the earth (perigee), unusually high and low tides occur, and the tidal range is greater than normal. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›When the moon is farthest from earth (apogee), the moon's gravitational force is limited, and the tidal ranges are less than their average heights. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›When the earth is closest to the sun (perihelion), around 3rd January each year, tidal ranges are much greater, with unusually high and unusually low tides. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›When the earth is farthest from the sun (aphelion), around 4th July each year, tidal ranges are much less than average. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›The time between high tide and low tide, when the water level is falling, is called the ebb. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›The time between low tide and high tide, when the tide is rising, is called the flow or flood. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Tides are helpful in desilting sediments and removing polluted water from river estuaries. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Tides are used to generate electrical power in countries like Canada, France, Russia, and China. A 3 MW tidal power project at Durgaduani in Sunderbans of West Bengal is underway. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›The Bay of Fundy (Canada) has the world's highest tidal range (up to 16 metres)
›In India, the Gulf of Khambhat (Cambay) has very high tidal range — potential for tidal energy
›Besides sodium chloride, other important dissolved compounds in seawater include magnesium, calcium, and potassium. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md
›The proportions of different salts in ocean water remain remarkably constant in all oceans and even to great depths due to the free movement of ocean water. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md
›Salinity variations in maps are shown by isohalines, which are lines joining places having an equal degree of salinity. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md
›The average salinity of the oceans is 35.2 parts per thousand. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md
›The average salinity of the Red
›
Surface currents constitute about 10% of all ocean water and are found in the upper 400 m of the ocean. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Deep water currents make up the other 90% of ocean water, moving around ocean basins due to variations in density and gravity, sinking at high latitudes where temperatures are cold enough to increase density. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Ocean currents are referred to by their "drift," which is measured in knots. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Currents are usually strongest near the surface, potentially attaining speeds over five knots, and generally slow down at depths to less than 0.5 knots. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›The oceanic circulation pattern roughly corresponds to the Earth’s atmospheric circulation pattern, mirroring anticyclonic flow in middle latitudes and cyclonic flow in higher latitudes. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›Warm currents bordering the west coasts of continents in middle and higher latitudes cause a distinct marine climate characterized by cool summers and relatively mild winters with a narrow annual temperature range. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›The mixing of warm and cold currents helps replenish oxygen and favors the growth of planktons, forming the best fishing grounds in the world. — NCERT Class 11 — India: Physical Environment, ch13-movements-of-ocean-water.md
›The oceans cover more than 70% or 364 million sq km of the Earth's surface. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.104)
›Ocean currents are defined as large masses of surface water that circulate in regular patterns around the oceans. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.109)
›Warm currents flow from equatorial regions polewards and have a higher surface temperature. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.109)
›Cold currents flow from polar regions equatorwards and have a lower surface temperature. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.109)
›Planetary winds are probably the dominant influence on the flow of ocean currents. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›The direction of currents in the North Indian Ocean changes completely with the direction of monsoon winds (north-east in winter, south-west in summer), providing strong evidence of wind influence. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›Waters of high salinity are denser than waters of low salinity, causing low salinity waters to flow on the surface and high salinity waters to flow at the bottom. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›The Earth's rotation deflects ocean currents to the right in the Northern Hemisphere (clockwise) and to the left in the Southern Hemisphere (anti-clockwise). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›Land masses obstruct and divert ocean currents, as seen with the tip of southern Chile diverting the West Wind Drift or Cape Sao Roque dividing equatorial currents. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›The Gulf Stream Drift is a strong current, 56-160 km wide, 610 meters deep, with a velocity of 5 km/hour. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›The North Atlantic Drift carries warm equatorial water to Europe's coasts, flowing at 16 km per day. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›Approximately two-thirds of the water brought by the Gulf Stream to the Arctic regions is returned annually to tropical latitudes by dense, cold polar water creeping southwards in the ocean depths. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›The Sargasso Sea is an area in the middle of the Atlantic with no perceptible current where a large amount of floating seaweed gathers. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch12-the-oceans.md (p.110)
›The Labrador Current carries icebergs southwards to meet the warm Gulf Stream off Newfoundland, as far south as 50°N, where they melt.
›
Landforms resulting from wind erosion processes (abrasion, deflation, attrition) include rock pedestals/mushroom rocks, zeugen, yardangs, ventifacts/dreikanter, and deflation hollows. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
Pangaea began to split around 200 million years ago, first into two large continental masses: Laurasia (northern component) and Gondwanaland (southern component).
›Evidence for continental drift includes the "Jig-Saw-Fit" of shorelines, particularly Africa and South America, which was proved to be "quite perfect" by Bullard in 1964 when matched at the 1,000-fathom line.
›Radiometric dating shows ancient rocks (2,000 million years old) from the Brazil coast match those from western Africa.
›The earliest marine deposits along the coastlines of South America and Africa are of Jurassic age, suggesting the Atlantic Ocean did not exist prior to that time.
›Tillite (sedimentary rock formed from glacier deposits) from the Gondawana system in India has counterparts in Africa, Falkland Island, Madagascar, Antarctica, and Australia, providing unambiguous evidence of palaeoclimates and continental drifting.
›Rich placer deposits of gold on the Ghana coast, despite the absolute absence of source rock in the region, are believed to be derived from gold-bearing veins in Brazil when the two continents lay side by side.
›Identical species of fossils, such as Mesosaurus (a small reptile adapted to shallow brackish water), are found only in the Southern Cape province of South Africa and Iraver formations of Brazil, despite these locations being presently 4,800 km apart.
›Wegener suggested "pole-fleeing force" (due to Earth's rotation and equatorial bulge) and "tidal force" (due to attraction of the Moon and Sun) as the forces responsible for continental drift, though most scholars considered these forces to be "totally inadequate".
›Arthur Holmes in the 1930s discussed the possibility of convection currents operating in the mantle, generated by radioactive elements causing thermal differences.
›Post-World War II ocean floor mapping revealed that the ocean floor is not a vast plain but has significant relief, including submerged mountain ranges (mid-oceanic ridges) and deep trenches (mostly located closer to continent margins).
›Rocks from the oceanic crust are much younger (nowhere more than 200 million years old) than continental rocks (some formations are as old as 3,200 million years).
›Rocks equidistant from the crest of mid-oceanic ridges show similarities in period of formation, chemical compositions, and magnetic properties, with rocks closer to the ridges being youngest and having normal polarity.
›Sediments on the ocean floor are unexpectedly thin, with the sediment column nowhere found to be older than 200 million years.
›The ocean floor can be segmented into three major divisions: continental margins, deep-sea basins (abyssal plains), and mid-ocean ridges.
›Mid-oceanic ridges form an interconnected, submerged chain of mountains with a central rift system at the crest, which is a zone of intense volcanic activity.
›Abyssal plains are extensive plains lying between continental margins and mid-oceanic ridges, where continental sediments that move beyond the margins get deposited.
›Earthquake foci along mid-oceanic ridges are at shallow depths, whereas along the Alpine-Himalayan belt and the rim of the Pacific, earthquakes are deep-seated ones.
›Harry Hess (1961) proposed the "sea floor spreading" hypothesis, arguing that constant eruptions at oceanic ridge crests cause the rupture of the oceanic crust, with new lava wedging into it and pushing the crust on either side.
›Hess maintained that the ocean floor that gets pushed due to volcanic eruptions at the crest, sinks down at the oceanic trenches and gets consumed.
›McKenzie and Parker and also Morgan, independently developed the concept of Plate Tectonics in 1967.
›A tectonic plate (lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere, moving horizontally over the asthenosphere as a rigid unit.
›The lithosphere's thickness varies between 5-100 km in oceanic parts and about 200 km in continental areas.
›Plates are classified as continental or oceanic based on which portion (continental or oceanic lithosphere) occupies a larger area; e.g., Pacific plate is largely oceanic, Eurasian plate may be called continental.
›The Earth’s lithosphere is divided into seven major and several minor plates, surrounded by young fold mountain ridges, trenches, and/or faults.
›Seven major plates include: Antarctic and the surrounding oceanic plate; North American plate; South American plate; Pacific plate; India-Australia-New Zealand plate; Africa with the eastern Atlantic floor plate; and Eurasia and the adjacent oceanic plate.
›Important minor plates include: Cocos plate (between Central America and Pacific); Nazc
›
Orogeny, epeirogeny, earthquakes, and plate tectonics induce pressure, volume, and temperature (PVT) changes which in turn cause metamorphism of rocks.
›The intensity of exogenic geomorphic processes depends on the type and structure of rocks, including folds, faults, orientation and inclination of beds, presence of joints, hardness, chemical susceptibility of minerals, and permeability.
›Chemical weathering processes include solution, carbonation, hydration, oxidation, and reduction, and are sped up by the presence of water, air (oxygen and carbon dioxide), and heat.
›Physical weathering processes depend on applied forces such as gravitational forces (overburden pressure, load, shearing stress), expansion forces (temperature changes, crystal growth, animal activity), and water pressures (wetting and drying cycles).
›Most physical weathering processes are caused by thermal expansion and pressure release, leading to rock fracture.
›Biological weathering involves the contribution or removal of minerals and ions and physical changes due to organism growth or movement, including burrowing by earthworms, termites, and rodents, human activities like ploughing, decaying plant/animal matter producing acids, and plant roots exerting pressure.
›Exfoliation, a result of physical weathering, leads to flaking off of curved sheets from rocks or bedrock, forming smooth and rounded surfaces. Exfoliation domes result from unloading, and tors from thermal expansion.
›Weathering processes are responsible for breaking down rocks, preparing the way for the formation of regolith and soils, erosion, and mass movements.
›Weathering of rocks and deposits helps in the enrichment and concentration of valuable ores of iron, manganese, aluminium, and copper by removing other materials through chemical or physical leaching.
›Mass movements transfer rock debris down slopes solely under the direct influence of gravity; air, water, or ice do not carry the debris, though debris may carry these elements.
›Mass movements are active over weathered slopes but weathering is not a prerequisite for them to occur, though it aids the process.
›Mass movements do not come under erosion because geomorphic agents like running water, glaciers, wind, waves, and currents do not participate in them.
›Conditions that favour mass movements include weak unconsolidated materials, thinly bedded rocks, faults, steeply dipping beds, vertical cliffs, abundant precipitation, and scarcity of vegetation.
›Activating causes for mass movements include removal of support, increase in gradient and height of slopes, overloading (natural or artificial), heavy rainfall and saturation of slope materials, earthquakes, excessive natural seepage, and indiscriminate removal of natural vegetation.
›Slump is a type of landslide involving the slipping of rock debris with a backward rotation relative to the slope.
›Debris slide is the rapid rolling or sliding of earth debris without backward rotation.
›Rock fall is the free falling of rock blocks over any steep slope, occurring from the superficial layers of the rock face, distinguishing it from rockslide which affects deeper materials.
›Debris avalanches and landslides occur frequently in the Himalayas due to tectonic activity, the presence of sedimentary rocks and unconsolidated deposits, and steep slopes.
›In the Western Ghats and Nilgiris, landslides and debris avalanches occur less frequently than in the Himalayas but are still present due to steep slopes, vertical cliffs, pronounced mechanical weathering, and heavy rainfall over short periods.
›Erosional agents like wind, running water, and glaciers are controlled by climatic conditions, representing gaseous, liquid, and solid states of matter, respectively.
›The work of waves is determined by location along the coastal region (interface of litho and hydro sphere), while the work of groundwater is determined more by the lithological character of the region (permeable and soluble rocks and water availability for karst topography).
›Deposition is a consequence of erosion, occurring when erosional agents lose velocity and energy on gentler slopes, causing materials to settle, with coarser materials deposited first.
›Soil formation (pedogenesis) depends first on weathering, with the weathering mantle being the basic input.
›Five basic factors control soil formation: parent material, topography, climate, biological activity, and time.
›Parent material and topography are passive control factors in soil formation.
›Climate is an important active factor in soil formation, with moisture (intensity, frequency, duration of precipitation, evaporation, humidity) and temperature (seasonal and diurnal variations) being key elements.
›In wet equatorial rainy a
›Barchans are prevalent in the deserts of Turkestan and the Sahara (ch07).
›They form transversely to the wind, with horns thinning out in the direction of the wind (ch07).
›A barchan has a convex, gently-sloping windward side and a concave, steep leeward (slip-face) side (ch07, Fig. 7.6).
›The crest of a barchan moves forward as sand is driven up the windward side and slips down the leeward side (ch07).
›The advancement rate of barchans varies from 8 meters per year for high dunes (up to 30m) to 15 meters per year for lower dunes (ch07).
›Barchans can encroach on oases, posing a threat to desert life (ch07).
›**Seifs** (longitudinal dunes) are long, narrow ridges of sand, often over a hundred kilometers long (ch07, Fig. 7.7).
›Seifs lie parallel to the direction of the prevailing winds and can attain heights of over 60 meters (ch07).
›Their crestline rises and falls like the teeth of a saw (ch07).
›Dominant winds blow along the corridors between seif dunes, keeping them clear of sand, while eddies drop sand to form the dunes (ch07).
›Prevailing winds increase the length of seifs, while occasional cross winds increase their height and width (ch07).
›Extensive seif dunes are found in the Sahara Desert (south of the Qattara Depression), the Thar Desert, and the West Australian Desert (ch07).
›**Loess** is fine dust blown beyond desert limits and deposited on neighboring lands (ch07).
›Loess is typically yellow, friable, and very fertile (ch07).
›It is fine loam, rich in lime, coherent, and extremely porous, allowing water to sink in readily (ch07).
›Streams can cut deep valleys through loess, potentially leading to badland topography (ch07).
›The most extensive loess deposit is in north-west China, covering an area of 650,000 sq km, with deposits 60 to 150 meters thick (ch07).
›In China, this yellowish wind-borne dust from the Gobi Desert is called 'Huangtu' or 'yellow earth' (ch07).
›The term 'loess' originated from a village in Alsace, France, where such deposits occur (ch07).
›Similar deposits are found in parts of Germany, France, and Belgium, locally called 'limon' (ch07).
›In parts of the Mid-West, U.S.A., loess derived from ice-sheets is termed 'adobe' (ch07).
›Temporary lakes formed in desert depressions, often rich in salts and glistening white when dry, are known as playas, salinas, or salars (in U.S. and Mexico) and shotts (in northern Africa). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›A "bajada" is a depositional feature composed of alluvial material laid down by intermittent streams. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›A "pediment" is an erosional plain at the base of surrounding mountain scarps. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›Coastal landforms depend upon (i) the configuration of land and sea floor; (ii) whether the coast is advancing (emerging) seaward or retreating (submerging) landward. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›For conceptual understanding, two types of coasts are considered: (i) high, rocky coasts (submerged coasts); (ii) low, smooth and gently sloping sedimentary coasts (emerged coasts). — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Along high rocky coasts, rivers appear drowned with highly irregular coastlines (often with fjords), hillsides drop sharply into the water, and erosional features dominate initially. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Along low sedimentary coasts, rivers extend their length by building coastal plains and deltas, the coastline appears smooth with occasional incursions of water (lagoons, tidal creeks), and depositional features dominate. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›The west coast of India is a high rocky retreating coast where erosional forms dominate. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›The east coast of India is a low sedimentary coast where depositional forms dominate. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A wave-cut terrace is a flat or gently sloping platform at the foot of sea cliffs, covered by rock debris, occurring at elevations above the average height of waves. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Sea caves are created by the lashing of waves against the base of cliffs and the abrasion of rock debris, which widen and deepen hollows. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Sea stacks are resistant masses of rock, originally parts of a cliff or hill, left standing isolated as small islands off the shore due to cliff retreat. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Beaches are temporary features, with sediment typically coming from land via streams/rivers or from wave erosion. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Beaches are mostly made of sand-sized materials, but shingle beaches contain small pebbles and even cobbles. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Sand dunes are deposited just behind the beach from sands lifted and winnowed from the beach surfaces, often forming long ridges parallel to the coastline along low sedimentary coasts. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›An off-shore bar is a ridge of sand and shingle formed in the sea in the off-shore zone, lying approximately parallel to the coast. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A barrier bar is an off-shore bar that becomes exposed due to further addition of sand. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Off-shore bars and barriers commonly form across the mouth of a river or at the entrance of a bay. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Spits can develop when barrier bars get keyed up to one end of a bay, or when they are attached to headlands/hills. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Lagoons form when barriers, bars, and spits extend across the mouth of a bay, eventually getting filled up by sediment from land or the beach to develop into a coastal plain. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Coastal off-shore bars offer the first buffer or defence against storm or tsunami by absorbing most of their destructive force. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Barriers, beaches, beach dunes, and mangroves (if any) also help absorb the destructive force of storm and tsunami waves. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›A wave-built terrace develops in front of a wave-cut terrace after a considerable period of cliff development and retreat, with the addition of more material to the offshore deposit. — NCERT Class 11 — India: Physical Environment, ch06-landforms-and-their.md
›Sinkholes vary in area from a few square meters to a hectare, and in depth from less than half a meter to thirty meters or more (NCERT ch06, p.52-53)
›Sinkholes can form solely through solution action (solution sinks) or by collapse of a cave roof (collapse sinks) (NCERT ch06, p.53)
›The term doline is sometimes used to refer to collapse sinks (NCERT ch06, p.53)
›Solution sinks are more common than collapse sinks (NCERT ch06, p.53)
›Surface run-off often goes down swallow and sink holes to flow as underground streams (NCERT ch06, p.53)
›When sinkholes and dolines join due to slumping or roof collapse, long trenches called valley sinks or Uvalas form (NCERT ch06, p.53)
›Lapies are extremely irregular surfaces with a maze of points, grooves, and ridges, formed by differential solution activity along joints (NCERT ch06, p.53)
›Lapie fields may eventually turn into somewhat smooth limestone pavements (NCERT ch06, p.53)
›Cave formation is prominent where limestones are dense, massive, and occur as thick beds, or interbedded with other rocks like shales and sandstones (NCERT ch06, p.53)
›Caves having openings at both ends are called tunnels (NCERT ch06, p.53)
›Stalactites are typically broad at their bases and taper towards their free ends (NCERT ch06, p.53)
›Stalagmites form due to dripping water from the surface or through stalactites (NCERT ch06, p.53)
›Stalagmites can take the shape of a column, a disc, a smooth rounded bulging end, or a miniature crater-like depression (NCERT ch06, p.53)
›Limestone and chalk are sedimentary rocks of organic origin derived from the accumulation of corals and shells in the sea (p.76)
›Chalk is a very pure, white, and rather soft form of limestone (p.76)
›Karst regions generally have a bleak landscape, occasionally broken by precipitous slopes (p.76)
›Streams rising on other rocks only flow over limestone for a short distance and then disappear underground (p.76)
›A resurgence occurs when water penetrates to the base of the limestone and meets non-porous rocks (p.76)
›Limestone pavements may have been formed beneath the soil and are now exposed by the removal of the soil cover (p.76-77)
›Swallow holes are small depressions carved out by solution where rain-water sinks into the limestone at a point of weakness (p.77)
›A doline can be formed where a number of swallow holes coalesce (p.77)
›Uvalas can be a kilometre across, containing much clayey soil from weathered limestones after their subsidence (p.77)
›Poljes, which can be as large as 100 square kilometres, are partly due to faulting; their drier areas are fertile and may support large villages (p.77-78)
›Limestone caves and caverns may contain ponds and lakes (p.78)
›Stalactites form as water carrying calcium in solution evaporates, leaving behind solidified crystalline calcium carbonate (p.79)
›Stalagmites are shorter, fatter, and more rounded compared to stalactites (p.79)
›Major limestone regions include the Causses district of southern France, the Pennines of Britain (Yorkshire and Derbyshire), the Kentucky region of the United States, the Yucatan Peninsula of Mexico, the Cockpit Country of Jamaica, and the limestone hills of Perlis, Peninsular Malaysia (p.79)
›Karst regions are often barren and carry a thin layer of soil, with porosity and absence of surface drainage making vegetative growth difficult, usually supporting only poor grass and short turf (p.79)
›Limestone vegetation in tropical regions, however, is luxuriant due to heavy rainfall all the year round (p.79)
›Settlements in karst regions are scattered, and the population is often sparse (p.79)
›Lead is the only mineral of importance found in veins in association with limestone in karst regions (p.79)
›Good quality limestones are often used as building materials or quarried for the cement industry (p.79)
›In Peninsular Malaysia, limestone outcrops of the Kledang Range and the Main Range are quarried for the Pan-Malaysia and Tasek Cement Works (p.79)
›Chalk landforms include low-rounded hills ('downs' in S England and N France) covered with short turf, sometimes woodland, used for pasture and sometimes arable farming (p.79)
›Due to the friable nature of chalk, swallow holes and underground cave networks do not generally develop (p.79)
›**Mesas**: Flat, table-like landmasses with a very resistant horizontal top layer and very steep sides, resisting denudation by wind and water. Examples include those in Arizona or Table Mountain in Cape Town, South Africa. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Buttes**: Isolated flat-topped hills resulting from the continued denudation and reduction in area of mesas. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Inselberg**: A German term meaning 'island-mountain', referring to isolated residual hills rising abruptly from level ground, characterized by steep slopes and rounded tops, often composed of granite or gneiss. Examples include northern Nigeria, Western Australia, and the Kalahari Desert, and Ayers Rock in the Australian Desert. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Ventifacts (Dreikanter)**: Pebbles faceted, shaped, and polished by sand-blasting, often with characteristic flat facets and sharp edges. Dreikanter specifically refers to those with three wind-faceted surfaces. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›**Deflation Hollows**: Depressions formed when winds blow away unconsolidated materials, lowering the ground surface. If the water-table is reached, water may seep out, forming oases or swamps. Examples include the Qattara Depression in the Sahara Desert (almost 135 meters below sea-level) and the Faiyum Depression in Egypt (40 meters below sea-level). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch07-arid-or-desert-landforms.md
›The Caspian Sea is almost 5 times larger than its nearest rival, Lake Superior. (p.82)
›The East African Rift Valley runs through Zambia, Malawi, Tanzania, Kenya and Ethiopia, and extends along the Red Sea to Israel and Jordan over a total distance of 4,800 km. (p.82)
›Kettle lakes are irregular because of the uneven morainic surface and are never of any great size or depth; examples include the meres of Shropshire (England) and kettle-lakes of Orkney (Scotland). (p.82)
›Rock-hollow lakes are abundant in Finland, a country the Finns call Suomi - the Land of Lakes. (p.82)
›Both lateral and terminal moraines are capable of damming valleys to form moraine-dammed lakes. (p.82)
›Volcanic craters can be enlarged by subsidence into a caldera; these depressions are normally dry, bounded by steep cliffs, and roughly circular in shape. (p.83)
›Lakes due to subsidence of a volcanic land surface form when the crust of a hollow lava flow collapses, leaving a wide and shallow depression. (p.83)
›Karst lakes form in solution hollows carved out by the solvent action of rain-water on limestone, which can become clogged with debris. (p.84)
›Large depressions called poljes, which normally do not have surface outlets, may contain karst lakes that shrink during dry periods due to seepage and cover most of the polje floor during wet periods. (p.84)
›Solution also forms lakes in other rocks like rock salt, with meres of Cheshire, England, likely caused by this and salt-mining operations. (p.84)
›Ox-bow lakes occur on the flood-plains of the Lower Mississippi, U.S.A. and Rio Grande Mexico. (p.84)
›Coastal lagoons can be isolated by spits or bars built by wind and wave action, and may drain away at low tide. (p.84)
›Lagoons are called haffs in East Germany and Poland. (p.84)
›Coastal sand dunes pushed landwards by strong on-shore winds can enclose marshy lagoons, as seen in the Landes of south-west France. (p.84)
›Barrier lakes are formed by landslides, screes, and avalanches blocking valleys, damming rivers. (p.84)
›Barrier lakes are short-lived because the loose fragments forming the dam will soon give way under water pressure, causing floods. (p.85)
›Examples of barrier lakes include Lake Gormire in Yorkshire (landslides) and Ffynnon Frech on Snowdon (screes). (p.85)
›Man-made lakes (artificial lakes or reservoirs) are created by erecting concrete dams across river valleys to retain river water. (p.85)
›An imposing example of a man-made lake is Lake Mead above the Hoover Dam on the Colorado River, U.S.A. (p.85)
›Lakes can be made by animals, such as beaver dams constructed across rivers with timber, forming permanent lakes like Beaver Lake in Yellowstone National Park, U.S.A. (p.85)
›Other types of man-made lakes include ornamental lakes (e.g., Lake Gardens in Kuala Lumpur, Taiping Lakes), those created by mining activities (e.g., tin mining in Peninsular Malaysia), and lakes for inland fish culture. (p.85)
›
Icebergs: only 1/9 of mass visible above water surface (p.58)
›Nunatak = mountain peak projecting above ice cap surface (p.58)
›Cirque in French = Corrie in Scotland = Cwm in Wales (p.61)
›Glaciers move because of the force of gravity, typically a few centimetres to a few metres a day (ch06-landforms-and-their.md)
›India has many glaciers in the Himalayas, specifically in the higher reaches of Uttaranchal, Himachal Pradesh, and Jammu and Kashmir (ch06-landforms-and-their.md)
›Cirques can contain a lake of water after the glacier disappears, known as cirque or tarn lakes (ch06-landforms-and-their.md)
›Two or more cirques can exist in a stepped sequence, one leading into another down below (ch06-landforms-and-their.md)
›Matterhorn (Alps) and Mount Everest (Himalayas) are examples of horns formed through headward erosion of radiating cirques (ch06-landforms-and-their.md)
›Arêtes are serrated or saw-toothed ridges with a very sharp crest and a zig-zag outline, formed by progressive erosion of divides between cirque side walls or head walls (ch06-landforms-and-their.md)
›Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, steep sides (ch06-landforms-and-their.md)
›Glacial valleys may contain littered debris or debris shaped as moraines, often with a swampy appearance (ch06-landforms-and-their.md)
›Lakes can be gouged out of rocky floors or formed by debris within glacial valleys (ch06-landforms-and-their.md)
›Hanging valleys are at an elevation on one or both sides of the main glacial valley (ch06-landforms-and-their.md)
›The faces of divides or spurs of hanging valleys are often truncated, appearing as triangular facets (ch06-landforms-and-their.md)
›Fjords are very deep glacial troughs filled with sea water, making up shorelines in high latitudes (ch06-landforms-and-their.md)
›Glacial till is unassorted coarse and fine debris dropped by melting glaciers, with most rock fragments being angular to sub-angular (ch06-landforms-and-their.md)
›Glacio-fluvial deposits (outwash deposits) are formed by meltwater streams, are roughly stratified, assorted, and have somewhat rounded rock fragments (ch06-landforms-and-their.md)
›Moraines are long ridges of glacial till deposits (ch06-landforms-and-their.md)
›Terminal moraines are long ridges of debris deposited at the end (toe) of glaciers (ch06-landforms-and-their.md)
›Lateral moraines form along the sides parallel to glacial valleys and may join a terminal moraine to form a horseshoe-shaped ridge (ch06-landforms-and-their.md)
›Ground moraines are irregular sheets of till left over valley floors by rapidly retreating valley glaciers, varying greatly in thickness and surface topography (ch06-landforms-and-their.md)
›Medial moraines form in the centre of glacial valleys, flanked by lateral moraines, and are often imperfectly formed (ch06-landforms-and-their.md)
›Eskers are sinuous ridges of very coarse materials (boulders, blocks) along with minor rock debris, deposited by meltwater streams flowing in channels beneath the ice (ch06-landforms-and-their.md)
›Outwash plains are formed at the foot of glacial mountains or beyond continental ice sheets by glacio-fluvial deposits, appearing as broad flat alluvial fans of gravel, silt, sand, and clay (ch06-landforms-and-their.md)
›Drumlins are smooth, oval-shaped, ridge-like features mainly composed of glacial till with some gravel and sand, typically up to 1 km long and 30 m high (ch06-landforms-and-their.md)
›The long axes of drumlins are parallel to the direction of ice movement (ch06-landforms-and-their.md)
›Drumlins have a blunter, steeper 'stoss end' facing the glacier and a 'tail' end (ch06-landforms-and-their.md)
›Drumlins form from rock debris dumped beneath heavily loaded ice through fissures, with the stoss end blunted by moving ice (ch06-landforms-and-their.md)
›Drumlins can indicate the direction of glacier movement (ch06-landforms-and-their.md)
Peneplain = erosional plain ('almost-plain') formed in humid conditions (p.24)
›Deccan Plateau has manganese, coal, iron deposits (p.24)
›The mean thickness of oceanic crust is 5 km, while that of the continental crust is around 30 km. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›The continental crust can be as much as 70 km thick in major mountain systems like the Himalayan region. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›The mantle extends from Moho’s discontinuity to a depth of 2,900 km. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›The upper portion of the mantle, called the asthenosphere, is considered a weak zone ("astheno" means weak) extending up to 400 km and is the main source of magma. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›The lithosphere comprises the crust and the uppermost part of the mantle, with a thickness ranging from 10-200 km. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›The lower mantle extends beyond the asthenosphere and is in a solid state. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›The core-mantle boundary is located at a depth of 2,900 km. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›The outer core is in a liquid state while the inner core is in a solid state, primarily composed of nickel and iron (nife layer). — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Igneous rocks are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling within the crust). — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Batholiths are large dome-shaped bodies of magmatic material that cool at deeper depths within the crust, appearing on the surface after denudational processes, and are typically granitic, representing cooled magma chambers. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Laccoliths are large dome-shaped intrusive bodies with a level base, connected by a pipe-like conduit from below, and can be seen in the domal hills of granite rocks on the Karnataka plateau. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Lapoliths are saucer-shaped intrusive bodies, concave to the sky, formed when lava moves horizontally into a weak plane. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Phacoliths are wavy masses of intrusive rocks found at the base of synclines or at the top of anticlines in folded igneous country. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Sills are thick horizontal deposits of intrusive igneous rocks, while thinner horizontal deposits are called sheets. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Dykes are wall-like structures formed when lava solidifies almost perpendicular to the ground in cracks and fissures, commonly found in Western Maharashtra, and are considered feeders for eruptions that led to the development of the Deccan traps. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Shield volcanoes are the largest volcanoes on Earth (barring basalt flows), mostly made of fluid basalt lava, characterized by low explosivity (unless water enters the vent), with Hawaiian volcanoes being famous examples. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Composite volcanoes are characterized by eruptions of cooler and more viscous lavas, often resulting in explosive eruptions along with large quantities of pyroclastic material and ashes, accumulating in layers. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Calderas are the most explosive volcanoes, tending to collapse on themselves when they erupt rather than building tall structures, forming collapsed depressions indicating huge, nearby magma chambers. — NCERT Class 11 — India: Physical Environment, ch03-fundamentals-of-physical-geography.md
›Flood Basalt Provinces are formed by highly fluid lava that flows for long distances, covering thousands of square kilometers with thick basalt lava flows, with the Deccan Traps in India being a much larger flood basalt province. — NCERT Class 11 — India: Physical Environment,
›The Coriolis Force is absent along the equator but increases progressively towards the poles; this is known as Ferrel's Law of Deflection — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Bay of Bengal receives more cyclones than Arabian Sea (roughly 5:1 ratio)
›Cyclonic season on the Indian coasts: April-June and October-December
›Temperature inversion is associated with anticyclonic conditions
›Frontal cyclones (temperate) form along the polar front — key to western disturbances affecting north India in winter
›Extra-tropical cyclones are systems developing in the mid and high latitudes, beyond the tropics — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Extra-tropical cyclones have a clear frontal system, unlike tropical cyclones — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Extra-tropical cyclones cover a larger area and can originate over both land and sea, whereas tropical cyclones originate only over the seas and dissipate on land — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Tropical cyclones have much higher wind velocity and are more destructive compared to extra-tropical cyclones — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Extra-tropical cyclones move from west to east, while tropical cyclones move from east to west — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Over low-pressure areas, air generally converges and rises; over high-pressure areas, air subsides from above and diverges at the surface — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Tropical cyclones are also known as Willy-willies in Western Australia — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Favourable conditions for tropical storm formation include: a large sea surface with temperature higher than 27° C, presence of the Coriolis force, small variations in vertical wind speed, a pre-existing weak-low-pressure area or low-level-cyclonic circulation, and upper divergence above the sea-level system — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›The place where a tropical cyclone crosses the coast is called the landfall of the cyclone — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Tropical cyclones that cross 20°N latitude generally recurve and are more destructive — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›The diameter of a mature tropical cyclonic system can vary between 150 and 250 km — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›The diameter of tropical storms over the Bay of Bengal, Arabian Sea, and Indian Ocean is typically between 600 - 1200 km — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Tropical cyclone systems move slowly, about 300 - 500 km per day — NCERT Class 11 — India: Physical Environment, ch09-atmospheric-circulation.md
›Tropical cyclones are also known as tornadoes in the Guinea lands of West Africa and the southern U.S.A. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Typhoons (a type of tropical cyclone) occur mainly between 6° and 20° north and south of the equator — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Typhoons are most frequent from July to October — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Typhoons have a diameter of only 80 to 320 km (50 to 200 miles) and a much steeper pressure gradient than temperate cyclones — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Violent winds with a velocity of over 160 km/h are common in typhoons — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Hurricanes have calm, rainless centers where the pressure is lowest (about 965 mb) — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Around the 'eye' of a hurricane, the wind strength can exceed force 12 of the Beaufort Scale (120 km/h) — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch14-climate.md
›Tornadoes are very violent tropical and sub-tropical cyclones in which the air spi
›Horizontal winds near the Earth's surface are influenced by the pressure gradient force, the frictional force, and the Coriolis force, in addition to the downward gravitational force.
›The pressure gradient is the rate of change of pressure with respect to distance; it is strong where isobars are close and weak where they are far apart.
›Frictional force is greatest at the surface, extending its influence up to 1-3 km, and is minimal over the sea surface.
›The Coriolis force is directly proportional to the angle of latitude, being maximum at the poles and absent at the equator.
›The deflection caused by the Coriolis force is greater when the wind velocity is higher.
›The Coriolis force acts perpendicular to the pressure gradient force.
›Tropical cyclones do not form near the equator because the Coriolis force is zero there, preventing the intensification of low-pressure systems.
›Winds in the upper atmosphere (2-3 km above surface) are largely free from frictional effects and are primarily controlled by the pressure gradient and Coriolis force.
›A geostrophic wind occurs when isobars are straight, there is no friction, and the pressure gradient force is balanced by the Coriolis force, causing the wind to blow parallel to the isobar.
›In the Northern Hemisphere, cyclonic (low pressure) circulation is anticlockwise, and anticyclonic (high pressure) circulation is clockwise.
›In the Southern Hemisphere, cyclonic circulation is clockwise, and anticyclonic circulation is anticlockwise.
›Over low-pressure areas, air converges and rises; over high-pressure areas, air subsides from above and diverges at the surface.
›The general circulation of the atmosphere is determined by latitudinal variation of atmospheric heating, emergence and migration of pressure belts, distribution of continents and oceans, and the Earth's rotation.
›The Hadley Cell involves air rising at the ITCZ due to high insolation, moving towards the poles at 14 km altitude, accumulating and sinking at 30° N/S (forming subtropical highs), and returning to the equator as easterlies near the surface.
›The Ferrel Cell in the middle latitudes involves sinking cold air from the poles and rising warm air from the subtropical high, with surface winds known as westerlies.
›The Polar Cell involves cold, dense air subsiding near the poles and blowing towards middle latitudes as polar easterlies.
›These three atmospheric cells are responsible for transferring heat energy from lower to higher latitudes, maintaining general circulation.
›The pressure belts are not permanent and oscillate with the apparent movement of the sun, moving southwards in the Northern Hemisphere winter and northwards in summer.
›The barometer for measuring pressure was invented by Galileo and his assistant Torricelli in 1643. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›An ordinary mercury barometer consists of a long glass tube, sealed at the upper and open at the lower end, with the lower end inverted in a bowl of mercury whose surface is exposed to the air. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›Mercury is chosen for barometers because it is the heaviest liquid known; if ordinary water were used, the corresponding column for normal atmospheric pressure would be 10 metres (34 feet). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›At sea-level, the mercury column in a barometer is typically 760 mm (29.9 inches). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›When pressure increases, the mercury column can rise to about 790 mm (31 inches) (high pressure), and when it decreases, it can drop to about 700 mm (28 inches) (low pressure). — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›The millibar (mb) was adopted as a new unit for measuring atmospheric pressure by meteorological stations in 1914. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›Normal atmospheric pressure, equivalent to 1.03 kg per cm² (14.7 lb. per square inch) or 760 mm (29.9 inches) of mercury, is 1013 millibars. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›In temperate latitudes, pressure changes are very rapid in the formation of cyclones and anticyclones, with normal variations ranging from 960 mb to 1040 mb. — GC Leong — Certificate Physical and Human Geography (3rd Ed), ch13-weather.md
›A sea-level barometer reading of 76 cm (29.9 inches) will be halved on mountainous regions at 5.6