Landforms, Weathering and Erosion: Notes and PYQs

The correct answer is B, soil erosion. Bad lands are stretches of land cut into a close network of deep gullies and sharp ridges, so dissected that cultivation becomes impossible, and they are produced when running water removes the topsoil through sheet wash that concentrates first into rills and then into gullies. The Chambal ravines of Madhya Pradesh, Rajasthan and Uttar Pradesh are the Indian textbook example. Option A, scanty rainfall, is wrong because bad lands need intense, concentrated runoff on loose material, and they occur in areas of heavy seasonal downpours rather than in the driest tracts. Option C, excessive forest cover, is the opposite of the truth: a thick cover of roots and leaf litter binds soil and breaks the force of raindrops, so forests prevent gullying. Option D, open defecation, is a sanitation problem with no role in shaping gullies. Note that the same question is sometimes asked with the word ravine instead of bad land; the answer stays the same.

The correct answer is D, overgrazing. Overgrazing strips the protective cover of grass, loosens the surface with hooves and leaves bare soil exposed to rain and wind, so it is one of the leading causes of soil erosion in dry India, never a remedy. Option A, intercropping, grows two or more crops together in alternate rows so that the ground is never left bare, which cuts the force of falling rain and is a recognised conservation practice. Option B, shelter belts, are rows of trees planted across the prevailing wind, used in Rajasthan and in the coastal tracts to slow the wind and stop deflation of sandy soil. Option C, a rock dam, is a low barrier of rocks built across a gully so that water slows, drops its silt and stops cutting the channel deeper. Questions of this kind usually list three genuine measures and one cause of degradation, so read the stem for the word NOT.

The correct answer is B, II, IV, III and I. Water erosion passes through stages, and the soil lost grows at every stage. Splash erosion, numbered II, is the first and mildest: raindrops strike bare soil and knock single particles a few centimetres away. Sheet erosion, numbered IV, follows when the dislodged material is carried off as a thin film of water over the whole surface. Rill erosion, numbered III, begins when that flow gathers into small channels a few centimetres deep that a plough can still erase. Gully erosion, numbered I, is the final and most destructive stage, in which the rills deepen into permanent ravines and the field goes out of use. So the increasing order is splash, sheet, rill and gully, which is option B. Option A and option C both place gully or rill ahead of splash, and option D wrongly puts rill before sheet, so none of them matches the recognised sequence.

The correct answer is B, physical weathering. Exfoliation is caused by repeated heating and cooling of the outer layer of a rock and by the release of pressure when overlying material is removed; the surface expands and contracts more than the interior and splits away as curved sheets. No change in the chemical composition of the rock takes place, and nothing is transported, so the process is mechanical weathering in place. Option A, chemical weathering, would require reactions such as carbonation, hydrolysis or oxidation that alter the minerals themselves, as in the solution of limestone. Option C, glacial erosion, involves moving ice that plucks and abrades rock, producing cirques and U-shaped valleys, not onion-skin shells. Option D, wind deposition, builds dunes and loess sheets and is a depositional process, the opposite of breaking rock down. Remember the rule that decides most questions in this chapter: weathering breaks rock where it stands, erosion carries the pieces away.

The correct answer is C, groundwater. Rainwater charged with carbon dioxide becomes a weak carbonic acid, seeps along joints in limestone and dissolves calcium carbonate by carbonation. Inside a cavern the dripping water loses carbon dioxide and redeposits that calcium carbonate, building stalactites downward from the roof, stalagmites upward from the floor, and a pillar where the two meet. The whole family of such features belongs to karst topography. Option A, wind, produces mushroom rocks, yardangs, dunes and loess, all in dry regions with bare surfaces. Option B, glacier, carves cirques, aretes, horns and U-shaped valleys and deposits moraines and drumlins. Option D, sea waves, cut cliffs, caves, arches and stacks along a coast and build beaches, spits and lagoons. A useful memory hook is that a stalactite holds tight to the ceiling while a stalagmite might grow up from the ground.

The correct answer is B, a meandering river cutting off a loop. In its middle and lower course a river swings from side to side, eroding the outer bank of each bend and depositing on the inner bank. The neck of a loop grows narrower until a flood cuts straight across it; the abandoned loop is sealed off by silt and survives as a crescent-shaped lake, the ox-bow. Option A describes a cirque or a tarn, both glacial hollows of the high mountains, which are circular rather than crescent-shaped. Option C, wind deflation, scoops shallow basins in deserts that hold water only briefly and are not loop-shaped. Option D describes a caldera lake, such as Lonar in Maharashtra, which is formed in a crater and has nothing to do with river bends. Examiners often pair this with the fact that ox-bow lakes are common on the flood plains of the Ganga and the Brahmaputra.

The correct answer is B, northern China. Loess is a depositional landform of wind: very fine silt lifted from desert and glacial margins is carried far away and settles as a yellow, porous, loosely packed sheet. The thickest and most extensive sheets on earth are in the loess plateau of northern China, which gives the Huang He its colour and its name, the Yellow River. Option A, Brazil, lies mostly in humid tropics where chemical weathering and thick forest cover prevent such deposition. Option C, Canada, carries glacial deposits such as moraines, drumlins and eskers, with only small patches of loess. Option D, Australia, has large deserts but its wind deposits take the form of long seif dunes rather than great loess sheets. A connected fact worth remembering is that loess soils are naturally fertile and self-draining, which is why the Chinese loess belt supports dense farming despite its extreme vulnerability to gully erosion.

The correct answer is C, moraine. A moraine is the ridge of unsorted rock debris that a glacier carries and dumps; it is named by position as lateral, medial, ground or terminal moraine, and the terminal moraine marks the farthest point the ice reached. Option A, a cirque, is an armchair-shaped hollow cut at the head of a glacial valley by plucking and abrasion, so it is erosional. Option B, an arete, is the sharp knife-edged ridge left where two cirques erode back towards each other, again erosional. Option D, a horn, is the pyramidal peak produced when three or more cirques eat into the same mountain mass, the Matterhorn being the classic example, and it too is erosional. The other depositional forms of ice that papers ask about are drumlins, eskers, kames and outwash plains, so a safe way to answer is to recall that erosion by ice hollows and sharpens, while deposition by ice piles up.

The correct answer is A, Slovenia. The term comes from the Kras or Karst plateau of the Dinaric region, which lies largely in present-day Slovenia and extends into the neighbouring coastal belt. The limestone there is riddled with sinkholes, dolines, swallow holes, caverns and underground streams, and geographers adopted the local name for every landscape where soluble rock is sculpted by groundwater. In India the Borra caves of Andhra Pradesh and the caves of the Meghalaya plateau show the same features. Option B, Greece, has extensive limestone but did not give the landform its name. Option C, Switzerland, is associated with alpine and glacial terms such as cirque and arete rather than with karst. Option D, Norway, is remembered for fjords, the drowned glacial troughs of its western coast. Examiners like to combine this question with the pairing of carbonation as the process and limestone or dolomite as the rock.

The correct answer is B, a deep glacial trough later invaded by the sea. A valley glacier reaching the coast scoops its floor below present sea level; when the ice melts and the sea rises, water floods the trough and leaves a long, narrow, steep-sided inlet with great depth. Norway, Chile, New Zealand and Greenland have the best examples. Option A is wrong because wind in deserts hollows shallow basins and shapes yardangs, and cannot cut a deep drowned valley. Option C describes a crater or caldera lake, such as Lonar in Maharashtra, which is circular and unconnected to the sea. Option D describes a gorge or canyon of river erosion, which keeps a V-shaped cross section rather than the U-shaped profile of glacial work. The cross section is the clue examiners rely on: a river cuts a V, a glacier widens it into a U, and a drowned U is a fjord.

The correct answer is B, chemical weathering. Abundant rainfall, warm temperatures and thick vegetation together supply the water, the heat and the organic acids that speed up solution, hydrolysis, hydration, carbonation and oxidation, so minerals are decomposed deeply. That is why the humid tropics carry thick red laterite crusts of iron and aluminium oxides and deep residual soils. Option A, frost weathering, needs repeated freezing and thawing of water in cracks and therefore belongs to high mountains and cold temperate lands. Option C, salt crystallisation, needs evaporation of salty moisture and is typical of arid and coastal regions. Option D, block disintegration, is a mechanical result of wide daily temperature ranges and so dominates hot deserts and cold rocky uplands. The pairing to memorise is simple: hot deserts give mechanical weathering, humid tropics give chemical weathering, and high latitudes and altitudes give frost action.