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English · हिन्दी · తెలుగు · தமிழ் · മലയാളം · मराठी · ಕನ್ನಡ

Weathering, mass movement and the work of rivers

ಕನ್ನಡದಲ್ಲಿ ವಿವರಣೆ

Geomorphology: plates, earthquakes, volcanoes and landforms · Part 3 / 4 · Fact-checked on · how we check

Written with AI from the sources listed at the bottom of this page, then fact-checked by a separate AI.

Physical, chemical and biological weathering, mass movement and India's landslide regions, how rivers erode, transport and deposit, the stages of a river, and the valleys, gorges, waterfalls, meanders, ox-bow lakes, floodplains, levees, alluvial fans, deltas and estuaries they create.

Each idea is explained first in Kannada (ಕನ್ನಡ), ending with the English and Hindi exam terms, followed by the same point in exam English. UPSC Prelims is in English or Hindi, so understand it in Kannada and revise it in English.

ಇಲ್ಲಿಯವರೆಗೆ ಒಳಗಿನ ಬಲಗಳು ಪರ್ವತಗಳನ್ನು ಎತ್ತುವುದನ್ನು ನೋಡಿದೆವು. ಈಗ ಬಹಿರ್ಜನ್ಯ ಬಲಗಳು — ಸೂರ್ಯನ ಶಾಖ, ಗುರುತ್ವ — ಆ ಎತ್ತರಗಳನ್ನು ನಿಧಾನವಾಗಿ ಸವೆಸುವುದನ್ನು ನೋಡೋಣ. ಇದು ಅಡುಗೆಯಂತೆ ಒಂದು ಕ್ರಮದಲ್ಲಿ ನಡೆಯುತ್ತದೆ: ಮೊದಲು ಕಲ್ಲು ಇದ್ದಲ್ಲೇ ಒಡೆಯುತ್ತದೆ, ನಂತರ ಸಡಿಲ ಮಣ್ಣು ಕೆಳಗೆ ಜಾರುತ್ತದೆ, ಕೊನೆಗೆ ನದಿ ಅದನ್ನು ಹೊತ್ತು ಬೇರೆಡೆ ಹಾಕುತ್ತದೆ. ನದಿಗಳು ಮಾಡುವ ಕಣಿವೆಗಳು, ಜಲಪಾತಗಳು, ತಿರುವುಗಳು, ಮುಖಜಭೂಮಿಗಳೂ ಈ ಭಾಗದಲ್ಲೇ. (→ English: exogenic forces · हिन्दी: बहिर्जात बल)

In exam EnglishThe first two parts dealt with forces from inside the Earth that raise mountains, open oceans and shake the ground. This part turns to the exogenic forces that work on the surface, powered by the Sun and by gravity, and that slowly wear the raised land down. The work proceeds in a sequence. Rock first breaks down where it lies; loosened material then slides or creeps downhill under its own weight; and running water, the most important agent of all, carries it away and lays it down elsewhere. This part follows that sequence, ending with the valleys, waterfalls, meanders and deltas that rivers create.

ಶಿಥಿಲೀಕರಣ ಎಂದರೆ ಕಲ್ಲು ಇದ್ದಲ್ಲೇ ಒಡೆದು ಪುಡಿಯಾಗುವುದು — ಯಾರೂ ಹೊತ್ತೊಯ್ಯುವುದಿಲ್ಲ. ಹೊತ್ತೊಯ್ದರೆ ಅದು ಸವೆತ. ಗೋಡೆಯ ಬಣ್ಣ ಬಿಸಿಲು-ಮಳೆಗೆ ಪದರಪದರವಾಗಿ ಉದುರುವುದು ಶಿಥಿಲೀಕರಣದಂತೆ; ಆ ಚಕ್ಕೆಗಳನ್ನು ಗಾಳಿ ಹಾರಿಸಿಕೊಂಡು ಹೋಗುವುದು ಸವೆತದಂತೆ. ಮೂರು ಬಗೆ: ಭೌತಿಕ (ಕಲ್ಲು ತುಂಡಾಗುತ್ತದೆ, ಖನಿಜ ಬದಲಾಗದು), ರಾಸಾಯನಿಕ (ಖನಿಜವೇ ಬದಲಾಗುತ್ತದೆ ಅಥವಾ ಕರಗುತ್ತದೆ), ಜೈವಿಕ. ಬಿಸಿ, ತೇವದ ಕಡೆ ರಾಸಾಯನಿಕ ವೇಗ; ಮರುಭೂಮಿ, ತಣ್ಣನೆಯ ಬೆಟ್ಟಗಳಲ್ಲಿ ಭೌತಿಕ. (→ English: weathering, erosion · हिन्दी: अपक्षय, अपरदन)

In exam Englishweathering is the breaking down of rock at or near the surface, in place, without the broken material being carried away. That last point separates it from erosion, which involves removal by water, ice, wind or waves. Weathering prepares the ground for erosion: it loosens rock so that the agents of erosion can move it, and it supplies the mineral particles from which soil forms over time. Geographers group it into physical (mechanical) weathering, in which rock is broken into smaller pieces without any change in its minerals; chemical weathering, in which the minerals themselves are altered or dissolved; and biological weathering, the work of plants, animals and microbes. Climate largely decides which kind dominates: chemical weathering is fastest in hot, wet regions, while physical weathering dominates in deserts and cold mountains.

ಭೌತಿಕ ಶಿಥಿಲೀಕರಣ ಒತ್ತಡದಿಂದ ನಡೆಯುತ್ತದೆ. ಫ್ರಿಡ್ಜ್‌ನಲ್ಲಿ ನೀರಿನ ಬಾಟಲಿ ತುಂಬಿಟ್ಟರೆ ಹೆಪ್ಪುಗಟ್ಟಿ ಒಡೆಯುತ್ತದಲ್ಲ — ಕಲ್ಲಿನ ಬಿರುಕುಗಳಲ್ಲಿ ನೀರು ಹಾಗೆಯೇ ಹೆಪ್ಪುಗಟ್ಟಿ ಬಿರುಕನ್ನು ಅಗಲ ಮಾಡುತ್ತದೆ. ಮರುಭೂಮಿಯಲ್ಲಿ ಹಗಲು ಬಿಸಿಯಾಗಿ ರಾತ್ರಿ ತಣ್ಣಗಾಗಿ ಕಲ್ಲು ಮತ್ತೆ ಮತ್ತೆ ಹಿಗ್ಗಿ ಕುಗ್ಗಿ ಸಡಿಲವಾಗುತ್ತದೆ. ಈರುಳ್ಳಿ ಸಿಪ್ಪೆಯಂತೆ ಮೇಲ್ಪದರಗಳು ಕಳಚುವುದು ಪದರ ಕಳಚುವಿಕೆ (ಎಕ್ಸ್‌ಫೋಲಿಯೇಶನ್). ಉಪ್ಪುನೀರು ರಂಧ್ರಗಳಲ್ಲಿ ಸೇರಿ ಹರಳುಗಳಾಗಿ ಬೆಳೆದು ಕಣಗಳನ್ನು ದೂರ ತಳ್ಳುತ್ತದೆ. (→ English: weathering, frost wedging, exfoliation · हिन्दी: अपक्षय, तुषार अपक्षय, अपपत्रण)

In exam EnglishPhysical weathering works by stress. In frost wedging, water seeps into cracks, freezes and expands by about nine per cent, prising the crack wider; repeated freezing and thawing shatters rock on cold mountain slopes. In hot deserts, rock surfaces heat strongly by day and cool sharply at night, and the repeated expansion and contraction loosens grains and flakes. Exfoliation is the peeling away of curved sheets from the surface of a rock mass, like the layers of an onion, often helped by the release of pressure as overlying rock is removed; it shapes rounded domes of granite. Salt crystallisation is important in deserts and on coasts: salty water enters pores, and the growing crystals force the grains apart.

ರಾಸಾಯನಿಕ ಶಿಥಿಲೀಕರಣ ಕಲ್ಲಿನ ಖನಿಜಗಳನ್ನೇ ಬದಲಿಸುತ್ತದೆ. ಉಪ್ಪು ನೀರಿನಲ್ಲಿ ಕರಗುವಂತೆ ಕೆಲವು ಖನಿಜಗಳು ಕರಗುತ್ತವೆ. ಮಳೆನೀರು ಕಾರ್ಬನ್ ಡೈಆಕ್ಸೈಡ್ ಹೀರಿ ದುರ್ಬಲ ಆಮ್ಲವಾಗಿ ಸುಣ್ಣದಕಲ್ಲನ್ನು ಕರಗಿಸುತ್ತದೆ. ಕಬ್ಬಿಣದ ಮೊಳೆ ತುಕ್ಕು ಹಿಡಿಯುವಂತೆ ಕಲ್ಲಿನಲ್ಲಿರುವ ಕಬ್ಬಿಣ ತುಕ್ಕು ಹಿಡಿದು ಕೆಂಪು, ಹಳದಿ ಬಣ್ಣ ಬರುತ್ತದೆ. ಕೆಲವು ಖನಿಜಗಳು ನೀರು ಹೀರಿ ಉಬ್ಬುತ್ತವೆ; ಕೆಲವು ನೀರಿನೊಂದಿಗೆ ವರ್ತಿಸಿ ಜೇಡಿಮಣ್ಣಾಗುತ್ತವೆ. ಮರದ ಬೇರುಗಳು ಬಿರುಕುಗಳನ್ನು ಅಗಲಿಸುತ್ತವೆ, ಕಲ್ಲುಹೂವು ಆಮ್ಲ ಬಿಡುತ್ತದೆ. (→ English: weathering, carbonation, oxidation, hydrolysis · हिन्दी: अपक्षय, कार्बनीकरण, ऑक्सीकरण, जल-अपघटन)

In exam EnglishChemical weathering changes the minerals of a rock. In solution, minerals such as rock salt simply dissolve in water. In carbonation, rainwater absorbs carbon dioxide and becomes a weak carbonic acid that dissolves limestone; this is the process behind karst caves, taught in the next part. In oxidation, iron in rocks combines with oxygen, much as an iron nail rusts, giving many weathered rocks and soils their red and yellow colours. In hydration, minerals take up water and swell, which strains the rock. In hydrolysis, water reacts with minerals such as feldspar in granite and turns them into clay. Biological weathering adds to both kinds: roots widen cracks as they grow, burrowing animals bring fresh rock to the surface, and lichens and decaying plants release acids that attack minerals.
Kinds of weathering
KindWhat happensProcessesFavoured by
Physical (mechanical)Rock breaks into pieces; minerals unchangedFrost wedging, heating and cooling, exfoliation, salt crystallisationDeserts, cold mountains
ChemicalMinerals altered or dissolvedSolution, carbonation, oxidation, hydration, hydrolysisHot, wet climates
BiologicalLiving things break or attack rockRoot growth, burrowing, acids from lichens and decaying plantsAreas with soil and vegetation

ರಾಶಿ ಚಲನೆ ಎಂದರೆ ಸಡಿಲ ಕಲ್ಲು, ಮಣ್ಣು ಗುರುತ್ವದಿಂದ ನೇರವಾಗಿ ಇಳಿಜಾರಿನಲ್ಲಿ ಕೆಳಗೆ ಸರಿಯುವುದು — ನೀರು ಹೊರುವುದಿಲ್ಲ, ಆದರೆ ಭಾರ ಹೆಚ್ಚಿಸಿ ಜಾರುವಂತೆ ಮಾಡುತ್ತದೆ. ಅತಿ ನಿಧಾನದ್ದು ಮಣ್ಣಿನ ತೆವಳುವಿಕೆ; ಬೇಲಿ ಕಂಬಗಳು, ಮರಗಳು ವಾಲಿದಾಗಲೇ ಗೊತ್ತಾಗುತ್ತದೆ. ಮಳೆಯಲ್ಲಿ ನೆನೆದ ಮಣ್ಣು ಗಟ್ಟಿ ದ್ರವದಂತೆ ಹರಿಯುವುದು ಕೆಸರು ಪ್ರವಾಹ; ದೊಡ್ಡ ಕಲ್ಲು-ಮಣ್ಣು ವೇಗವಾಗಿ ಜಾರುವುದು ಭೂಕುಸಿತ; ಬಂಡೆಯ ಅಂಚಿನಿಂದ ಕಲ್ಲು ಬೀಳುವುದು. ಕಡಿದಾದ ಇಳಿಜಾರು, ಭಾರೀ ಮಳೆ, ಕಾಡು ಕಡಿತ, ರಸ್ತೆಗಾಗಿ ಕೊರೆತ ಇದನ್ನು ಹೆಚ್ಚಿಸುತ್ತವೆ. (→ English: mass movement, soil creep, landslide · हिन्दी: वृहत् संचलन, मृदा सर्पण, भूस्खलन)

In exam Englishmass movement is the movement of weathered rock and soil down a slope under the direct pull of gravity, without being carried by water, ice or wind, although water often helps by adding weight and reducing friction. The slowest form is soil creep, a gradual downhill shift of soil that is noticed only when fence posts, walls and tree trunks begin to tilt. In cold regions, solifluction is the slow flow of waterlogged soil over ground that stays frozen below. Faster forms include mudflows, in which soil soaked by heavy rain pours down like a thick liquid; slumping, a block slipping and rotating backwards on a curved surface; landslides, the rapid sliding of large masses of rock and earth; and rockfalls, the free fall of rock from cliffs. Steep slopes, heavy rain, earthquakes, the clearing of forests, road cutting and the undercutting of slopes by rivers all make such movements more likely.

ನಮ್ಮ ದೇಶದಲ್ಲಿ ಭೂಕುಸಿತ ಹೆಚ್ಚು ಆಗುವ ಎರಡು ಪ್ರದೇಶಗಳು. ಹಿಮಾಲಯ ಹೊಸ ಪರ್ವತಗಳು — ಮಡಿಕೆ, ಬಿರುಕುಗಳಿಂದ ತುಂಬಿ ಇನ್ನೂ ಏರುತ್ತಿವೆ, ಭೂಕಂಪ ಆಗಾಗ; ಅವುಗಳ ಮೇಲೆ ಮುಂಗಾರು ಮಳೆ, ಜೊತೆಗೆ ರಸ್ತೆಗಾಗಿ ಕೊರೆದ ಇಳಿಜಾರುಗಳು — ಜೋಡಿಸಿದ ಇಟ್ಟಿಗೆ ರಾಶಿಯ ಕೆಳಗಿನ ಇಟ್ಟಿಗೆ ಎಳೆದಂತೆ. ಪಶ್ಚಿಮ ಘಟ್ಟಗಳಲ್ಲಿ ಕಡಿದಾದ ಇಳಿಜಾರು, ಕೆಲವೇ ದಿನಗಳಲ್ಲಿ ಭಾರೀ ಮಳೆ; ಗಟ್ಟಿ ಕಲ್ಲಿನ ಮೇಲಿನ ದಪ್ಪ ಮಣ್ಣು ನೀರು ತುಂಬಿ ಒಮ್ಮೆಲೇ ಜಾರುತ್ತದೆ — ವಯನಾಡ್ ಉದಾಹರಣೆ. (→ English: landslide, Himalaya, Western Ghats · हिन्दी: भूस्खलन, हिमालय, पश्चिमी घाट)

In exam EnglishIndia's two most landslide-prone regions show these causes at work. The Himalaya are young mountains of folded, faulted and fractured rock, still rising and shaken by frequent earthquakes; when monsoon rain falls on these unstable slopes, especially where roads and settlements have been cut into them, landslides block highways and dam rivers. The Western Ghats have steep slopes facing the south-west monsoon and receive very heavy rain within a few days; thick weathered soil over hard rock becomes saturated and can give way suddenly. The landslides of 30 July 2024 in Wayanad district of Kerala, are a recent example. The Geological Survey of India is the nodal agency for landslide studies, and the Landslide Atlas of India, published by ISRO's National Remote Sensing Centre in 2023, maps the areas most at risk.

ನದಿ ನಾಲ್ಕು ರೀತಿಯಲ್ಲಿ ಸವೆತ ಮಾಡುತ್ತದೆ: ನೀರಿನ ತಳ್ಳುವ ಬಲ; ನೀರಿನೊಂದಿಗೆ ಬರುವ ಬೆಣಚುಕಲ್ಲುಗಳು ಮರಳು ಕಾಗದದಂತೆ ತಳ, ದಡವನ್ನು ಉಜ್ಜುವುದು; ಆ ಕಲ್ಲುಗಳು ಒಂದಕ್ಕೊಂದು ತಾಗಿ ಚಿಕ್ಕದಾಗಿ, ದುಂಡಾಗುವುದು; ಕೆಲವು ಕಲ್ಲುಗಳು ಕರಗುವುದು. ಭಾರವನ್ನು ಕರಗಿಸಿ, ತೇಲಿಸಿ, ಜಿಗಿಸಿ, ಉರುಳಿಸಿ ಒಯ್ಯುತ್ತದೆ. ವೇಗ ಕಡಿಮೆಯಾದಾಗ — ತಿರುವಿನಲ್ಲಿ, ಬಯಲಿನಲ್ಲಿ, ಸಮುದ್ರದ ಬಳಿ — ಮೊದಲು ದೊಡ್ಡ ಕಲ್ಲು, ನಂತರ ನುಣ್ಣನೆ ಮಣ್ಣು ಬಿಡುತ್ತದೆ; ಅದೇ ನಿಕ್ಷೇಪಣ. ಸಮುದ್ರ ಮಟ್ಟಕ್ಕಿಂತ ಕೆಳಗೆ ನದಿ ಕೊರೆಯಲಾರದು. (→ English: erosion, deposition, base level · हिन्दी: अपरदन, निक्षेपण, आधार तल)

In exam EnglishRunning water does more to shape the land than any other agent. A river carries out erosion in four ways: hydraulic action, the sheer force of moving water; abrasion, in which pebbles and sand carried by the current scrape the bed and banks; attrition, in which the carried fragments knock against each other and become smaller and rounder; and solution, in which soluble rocks are dissolved. It transports its load in solution, in suspension (fine silt and clay held up in the water), by saltation (sand grains bouncing along) and by traction (boulders rolled along the bed). When the current slows, at a bend, on entering a plain or where it meets the sea, the river lays down its load, coarsest first; this is deposition. A river cannot cut below its base level, the lowest level to which it can erode; for most rivers this is sea level.

ನದಿಯ ಬದುಕು ಮನುಷ್ಯನ ಬದುಕಿನಂತೆ. ಯೌವನದಲ್ಲಿ — ಬೆಟ್ಟಗಳಲ್ಲಿ — ಇಳಿಜಾರು, ವೇಗ ಹೆಚ್ಚು, ಕೆಳಕ್ಕೇ ಕೊರೆದು ಆಳ ಕಣಿವೆಗಳು, ಜಲಪಾತಗಳು. ಮಧ್ಯವಯಸ್ಸಿನಲ್ಲಿ ಇಳಿಜಾರು ತಗ್ಗಿ, ಪಕ್ಕಕ್ಕೂ ಕೊರೆದು ಕಣಿವೆ ಅಗಲವಾಗುತ್ತದೆ, ತಿರುವುಗಳು ಶುರು. ವೃದ್ಧಾಪ್ಯದಲ್ಲಿ ಬಹುತೇಕ ಸಮತಟ್ಟಾದ ಬಯಲಿನಲ್ಲಿ ನಿಧಾನವಾಗಿ ದೊಡ್ಡ ತಿರುವುಗಳಲ್ಲಿ ಹರಿದು, ಕೊರೆಯುವುದಕ್ಕಿಂತ ಹೆಚ್ಚು ಹಾಕುತ್ತದೆ. ಬಹಳ ಕಾಲದಲ್ಲಿ ಪ್ರದೇಶವೆಲ್ಲ ಸವೆದು ಬಹುತೇಕ ಸಮತಟ್ಟಾದ ಮೇಲ್ಮೈ ಆಗುತ್ತದೆ; ಭೂಮಿ ಮತ್ತೆ ಏರಿದರೆ ನದಿಗೆ ಮತ್ತೆ ಯೌವನ. (→ English: youth, maturity, old age, peneplain, rejuvenation · हिन्दी: युवा, प्रौढ़, वृद्ध अवस्था, समप्राय मैदान, पुनर्युवन)

In exam EnglishA river's work changes along its course, and geographers describe this as stages of youth, maturity and old age. In its youthful upper course, near the source, the slope is steep, the channel narrow and the water fast; the river cuts mainly downward, carving deep valleys and leaving waterfalls and rapids. In maturity the slope eases, the river begins to cut sideways as well as down, the valley widens, and the river starts to swing in bends. In old age, on a nearly level plain, the river flows slowly in wide loops across a broad floodplain and deposits more than it erodes. Given enough time without uplift, a whole region could be worn down to a low, gently rolling surface called a peneplain, close to base level. If the land is uplifted, the river gains energy and begins cutting down again, which is called rejuvenation.
Stages of a river compared
StageSlope and speedMain workTypical landforms
Youth (upper course)Steep; fastCutting downV-shaped valleys, gorges, waterfalls, rapids, potholes
Maturity (middle course)ModerateCutting sideways as well as downWider valleys, meanders begin, floodplain starts
Old age (lower course)Very gentle; slowDeposition exceeds erosionWide meanders, ox-bow lakes, levees, floodplains, deltas

ನದಿಯ ಸವೆತದಿಂದ ಆಗುವ ರೂಪಗಳು. ನದಿ ಕೆಳಕ್ಕೆ ವೇಗವಾಗಿ ಕೊರೆದರೆ 'V' ಆಕಾರದ ಕಣಿವೆ. ತುಂಬಾ ಆಳವಾದ, ಕಿರಿದಾದ, ಲಂಬ ಗೋಡೆಗಳ ಕಣಿವೆ ಕಮರಿ (ಗಾರ್ಜ್); ಅದೇ ಬಹಳ ದೊಡ್ಡ ಪ್ರಮಾಣದಲ್ಲಿ, ಒಣ ಪ್ರದೇಶದಲ್ಲಿದ್ದರೆ ಕ್ಯಾನ್ಯನ್. ಗಟ್ಟಿ ಕಲ್ಲಿನ ಕೆಳಗೆ ಮೆದು ಕಲ್ಲಿದ್ದರೆ ಮೆದುವಾದದ್ದು ಬೇಗ ಸವೆದು ಮೆಟ್ಟಿಲು ಆಗಿ ಜಲಪಾತ — ಜೋಗ ಜಲಪಾತದಂತೆ. ಸುಳಿಯಲ್ಲಿ ತಿರುಗುವ ಬೆಣಚುಕಲ್ಲುಗಳು ಡ್ರಿಲ್ಲಿಂಗ್ ಯಂತ್ರದಂತೆ ತಳದಲ್ಲಿ ಗುಂಡಿ ಕೊರೆಯುತ್ತವೆ. ನದಿ ಮತ್ತೆ ಕೆಳಕ್ಕೆ ಕೊರೆದರೆ ಹಳೆಯ ಬಯಲು ಮೆಟ್ಟಿಲುಗಳಾಗಿ ಉಳಿಯುತ್ತದೆ — ನದಿ ಮೆಟ್ಟಿಲುಗಳು. (→ English: V-shaped valley, gorge, canyon, waterfall, pothole, river terrace · हिन्दी: V-आकार की घाटी, गॉर्ज, कैनियन, जलप्रपात, जलगर्तिका, नदी वेदिका)

In exam EnglishErosion by rivers produces a distinctive set of landforms. Where a river cuts down faster than weathering can widen the sides, it carves a V-shaped valley. A very deep, narrow valley with almost vertical sides is a gorge; a canyon is a gorge on a vast scale, typical of dry regions where the walls are not worn back by rain, such as the Grand Canyon in the United States. Waterfalls form where a river drops over a sudden step in its bed, often where a band of hard rock lies over softer rock that wears away faster; rapids are stretches of fast, broken water over a rocky bed. Jog Falls on the Sharavathi in Karnataka is a well-known Indian waterfall. Pebbles whirled round by eddies drill circular potholes into the bed, and a deep plunge pool forms at the foot of a waterfall. River terraces are step-like benches on a valley side, the remains of an older, higher floodplain left behind when the river cut down again.

ಸಮತಟ್ಟು ಪ್ರದೇಶದಲ್ಲಿ ನದಿ ಹಾವಿನಂತೆ ಅತ್ತಿತ್ತ ತಿರುಗುತ್ತಾ ಹರಿಯುತ್ತದೆ — ನದಿ ತಿರುವುಗಳು. ತಿರುವಿನ ಹೊರಭಾಗದಲ್ಲಿ ನೀರು ವೇಗವಾಗಿ ಹರಿದು ದಡ ಕೊರೆಯುತ್ತದೆ; ಒಳಭಾಗದಲ್ಲಿ ನಿಧಾನವಾಗಿ ಹರಿದು ಮರಳು ಹಾಕುತ್ತದೆ. ಎರಡು ತಿರುವುಗಳು ಹತ್ತಿರ ಬಂದರೆ ಪ್ರವಾಹದಲ್ಲಿ ನದಿ ಕುತ್ತಿಗೆ ಮುರಿದು ಹತ್ತಿರದ ದಾರಿ ಹಿಡಿಯುತ್ತದೆ; ಬಿಟ್ಟ ತಿರುವು ಕುದುರೆ ಲಾಳದ ಆಕಾರದ ಸರೋವರವಾಗುತ್ತದೆ. ಪ್ರವಾಹದಲ್ಲಿ ನದಿ ಪಕ್ಕದ ನೆಲದ ಮೇಲೆ ಮೆಕ್ಕಲು ಹರಡುತ್ತದೆ — ಪ್ರವಾಹ ಬಯಲು; ದಡದ ಬಳಿ ಒರಟು ಮಣ್ಣು ಕೂಡಿ ಸಹಜ ದಿಬ್ಬಗಳು. ಭಾರ ಹೆಚ್ಚಿ ನದಿ ಹಲವು ಕವಲುಗಳಾಗಿ ಒಡೆದರೆ ಜಡೆ ಹೆಣೆದಂತೆ — ಬ್ರಹ್ಮಪುತ್ರದಂತೆ. (→ English: meander, ox-bow lake, floodplain, natural levee, braided channel · हिन्दी: विसर्प, गोखुर झील, बाढ़ का मैदान, प्राकृतिक तटबंध, गुंफित धारा)

In exam EnglishOn gentle slopes a river swings from side to side in loops called meanders. Water flows fastest on the outside of each bend, so it erodes that bank into a steep river cliff, while slower water on the inside drops sand and gravel to form a point bar. When two bends come close, the river may break through the narrow neck during a flood and take the shorter path; the cut-off loop, sealed by sediment, becomes a crescent-shaped ox-bow lake. When the river overflows, it spreads silt over the land beside it and builds a flat, fertile floodplain. The coarsest material is dropped first, right at the edge of the channel, so repeated floods raise low ridges called natural levees along the banks. Where a river carries a heavy load and its flow varies greatly between seasons, it may split into many channels separated by sandbars, forming a braided channel, as the Brahmaputra does in Assam.

ನದಿಯ ವೇಗ ಒಮ್ಮೆಲೇ ಕಡಿಮೆಯಾಗುವಲ್ಲಿ ಇನ್ನೂ ಎರಡು ರೂಪಗಳು. ಬೆಟ್ಟದ ಕಣಿವೆಯಿಂದ ಬಯಲಿಗೆ ಧುಮುಕಿದಾಗ ಇಳಿಜಾರು ತಗ್ಗಿ, ಹೊತ್ತು ತಂದ ಜಲ್ಲಿ, ಮರಳನ್ನು ಬೀಸಣಿಗೆಯ ಆಕಾರದಲ್ಲಿ ಹರಡುತ್ತದೆ — ಮೆಕ್ಕಲು ಬೀಸಣಿಗೆ (ಕೋಸಿ ಉದಾಹರಣೆ). ಸಮುದ್ರ ಒಯ್ಯುವುದಕ್ಕಿಂತ ಹೆಚ್ಚು ಮಣ್ಣು ಬಂದರೆ ನದಿಮುಖದಲ್ಲಿ ಹಲವು ಕವಲುಗಳ ತ್ರಿಕೋನ ಬಯಲು — ಮುಖಜಭೂಮಿ; ಗಂಗಾ-ಬ್ರಹ್ಮಪುತ್ರ, ಗೋದಾವರಿ, ಕಾವೇರಿ. ಬಲವಾದ ಉಬ್ಬರವಿಳಿತ ಮಣ್ಣನ್ನು ಸಮುದ್ರಕ್ಕೆ ಗುಡಿಸಿದರೆ ಮುಖಜಭೂಮಿ ಆಗುವುದಿಲ್ಲ, ಆಲಿಕೆಯಾಕಾರದ ಅಳಿವೆ (ಎಸ್ಚುವರಿ) — ನರ್ಮದಾ, ತಾಪಿ. (→ English: alluvial fan, delta, estuary · हिन्दी: जलोढ़ पंख, डेल्टा, ज्वारनदमुख)

In exam EnglishTwo more landforms mark places where a river slows abruptly. Where a stream rushes out of a mountain valley onto a plain, the sudden drop in slope makes it shed its load in a fan-shaped spread of gravel and sand called an alluvial fan; the Kosi has built a very large one in north Bihar and Nepal. At the river's mouth, if the sea or lake cannot carry sediment away as fast as it arrives, the river builds a delta, a low, often triangular plain crossed by branching distributaries. The Ganga and Brahmaputra together have built the largest delta in the world, in West Bengal and Bangladesh, and the Mahanadi, Godavari, Krishna and Kaveri build deltas on India's east coast. Where strong tides scour the mouth and sweep sediment out to sea, no delta forms; the river instead ends in a funnel-shaped estuary. The west-flowing Narmada and Tapi, which run through rift valleys to the Arabian Sea, end in estuaries.

ಈ ಭಾಗವೆಲ್ಲ ಒಂದು ಸರಪಳಿ. ಶಿಥಿಲೀಕರಣ ಕಲ್ಲನ್ನು ಇದ್ದಲ್ಲೇ ಸಡಿಲ ಮಾಡುತ್ತದೆ, ರಾಶಿ ಚಲನೆ ಅದನ್ನು ಇಳಿಜಾರಿನಿಂದ ಕೆಳಗೆ ತರುತ್ತದೆ, ನದಿ ಮುಂದಕ್ಕೆ ಹೊತ್ತೊಯ್ಯುತ್ತದೆ — ಯೌವನದಲ್ಲಿ ಕಣಿವೆ, ಜಲಪಾತಗಳನ್ನು ಕೊರೆಯುತ್ತಾ, ವೃದ್ಧಾಪ್ಯದಲ್ಲಿ ಪ್ರವಾಹ ಬಯಲು, ಮುಖಜಭೂಮಿಗಳನ್ನು ಕಟ್ಟುತ್ತಾ. ರೈತನ ಹೊಲದ ಮೆಕ್ಕಲು ಮಣ್ಣು ಎಲ್ಲೋ ಬೆಟ್ಟದ ಕಲ್ಲಿನಿಂದಲೇ ಬಂದದ್ದು. ಮಳೆಗಾಲದಲ್ಲಿ ಹಿಮಾಲಯ, ಪಶ್ಚಿಮ ಘಟ್ಟಗಳಲ್ಲಿ ಭೂಕುಸಿತ, ಪೂರ್ವಕ್ಕೆ ಹರಿಯುವ ನದಿಗಳಿಗೆ ಮುಖಜಭೂಮಿ, ನರ್ಮದಾ-ತಾಪಿಗೆ ಅಳಿವೆ — ಎಲ್ಲವೂ ಇದೇ ಸರಪಳಿಯಿಂದ ಅರ್ಥವಾಗುತ್ತದೆ. (→ English: weathering, mass movement · हिन्दी: अपक्षय, वृहत् संचलन)

In exam EnglishSeen together, the processes in this part form a chain. weathering loosens rock in place, mass movement brings it down the slopes to the valley floor, and rivers carry it onward, cutting valleys, gorges and waterfalls where they are young and steep, and building floodplains, levees and deltas where they are old and slow. The same chain explains why landslides strike the Himalaya and the Western Ghats in the monsoon, why the plains of north India are deep in fertile alluvium, and why the east-flowing rivers of the peninsula end in deltas while the Narmada and Tapi end in estuaries. The next part completes the picture with glaciers, wind, groundwater and waves.

Exam traps

Recap

Practice questions

Q1. Which one of the following is a process of chemical weathering?

  1. Frost wedging
  2. Exfoliation
  3. Carbonation
  4. Salt crystallisation
Show answer

Answer: C. Carbonation

(c) is correct: in carbonation, rainwater with dissolved carbon dioxide forms a weak acid that dissolves limestone, changing its minerals. (a) is wrong because frost wedging breaks rock by the expansion of freezing water, a physical process. (b) is wrong because exfoliation is the peeling of rock sheets, also physical. (d) is wrong because growing salt crystals force grains apart mechanically without changing the minerals.

Q2. Consider the following statements:
1. Weathering involves the removal and transport of rock material by running water or wind.
2. Chemical weathering is generally fastest in hot and humid climates.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: B. 2 only

Statement 1 is wrong: weathering breaks rock down in place; removal and transport are erosion. Statement 2 is correct: warmth and moisture speed up the chemical reactions that alter minerals. So (a) and (c) accept a wrong statement, and (d) rejects a correct one.

Q3. The slowest form of mass movement, usually noticed only when fence posts and tree trunks begin to tilt, is

  1. rockfall
  2. soil creep
  3. mudflow
  4. slumping
Show answer

Answer: B. soil creep

(b) is correct: soil creep is a very slow, gradual downhill shift of soil. (a) is wrong because a rockfall is the sudden free fall of rock from a cliff. (c) is wrong because a mudflow is a fast flow of rain-soaked soil. (d) is wrong because slumping is the fairly rapid slip of a block along a curved surface.

Q4. Which of the following landforms are typical of the youthful (upper) course of a river?
1. Gorges
2. Waterfalls
3. Ox-bow lakes
4. Natural levees
Select the correct answer using the code given below:

  1. 1 and 2 only
  2. 3 and 4 only
  3. 1, 2 and 3 only
  4. 1, 2, 3 and 4
Show answer

Answer: A. 1 and 2 only

(a) is correct: in its steep upper course a river cuts downward, producing gorges and waterfalls. (b) is wrong because ox-bow lakes and natural levees are depositional features of the gentle lower course. (c) wrongly includes ox-bow lakes, and (d) wrongly includes both ox-bow lakes and levees.

Q5. Consider the following statements about a meandering river:
1. Erosion is greatest on the outer bank of a bend.
2. An ox-bow lake forms when the river cuts through the narrow neck of a meander.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: C. Both 1 and 2

Both statements are correct. Water flows fastest on the outside of a bend and erodes a river cliff there, while the slower inside builds a point bar. When the neck between two bends is breached, usually in a flood, the abandoned loop becomes an ox-bow lake. So (a), (b) and (d) each reject at least one correct statement.

Q6. Which one of the following rivers ends in an estuary rather than a delta?

  1. Mahanadi
  2. Godavari
  3. Kaveri
  4. Narmada
Show answer

Answer: D. Narmada

(d) is correct: the Narmada flows west through a rift valley into the Arabian Sea and ends in an estuary, where tides sweep sediment away. (a), (b) and (c) are wrong because the Mahanadi, Godavari and Kaveri flow east into the Bay of Bengal and build deltas.

Q7. Match List I (landform) with List II (description):
List I
A. Alluvial fan
B. Natural levee
C. Pothole
D. River terrace
List II
1. Circular hollow drilled in a riverbed by swirling pebbles
2. Step-like bench left by an older floodplain
3. Fan of sediment where a stream leaves the mountains
4. Low ridge built along the banks by floods
Select the correct answer using the code given below:

  1. A-3, B-4, C-1, D-2
  2. A-4, B-3, C-1, D-2
  3. A-3, B-4, C-2, D-1
  4. A-2, B-4, C-1, D-3
Show answer

Answer: A. A-3, B-4, C-1, D-2

(a) is correct: an alluvial fan is the sediment fan at the mountain foot, a levee the ridge along the banks, a pothole the hollow drilled by pebbles, and a terrace the bench left by an older floodplain. (b) swaps the fan and the levee. (c) swaps the pothole and the terrace. (d) swaps the fan and the terrace.

Q8. Consider the following statements:
1. The Himalaya are prone to landslides partly because they are young, fractured mountains affected by frequent earthquakes.
2. The Geological Survey of India is the nodal agency for landslide studies in India.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: C. Both 1 and 2

Both statements are correct. The Himalaya's young, folded and fractured rocks, frequent earthquakes and monsoon rain make their slopes unstable. The Geological Survey of India is the nodal agency for landslide studies. So (a), (b) and (d) each reject at least one correct statement.

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