Erosional and depositional landforms created by various agents

Correct answer: D. An alluvial fan forms where a steep, fast-flowing stream leaves a narrow mountain valley and spreads onto a flatter, wider plain. The sudden reduction in slope causes the stream to lose velocity. Because slower water has less carrying capacity, it deposits the gravel, pebbles, sand, and silt that it was transporting. The deposits spread outward from the valley mouth in a roughly fan-shaped pattern, often with channels branching across the surface. Option A describes neither the characteristic change in slope nor the required depositional setting. Option B concerns glacial deposition and does not explain a stream-built fan. Option C is coastal erosion, which removes material rather than creating this inland fluvial deposit. The sequence is: steep slope, plain, lower speed, reduced carrying capacity, deposition, fan shape.

The correct answer is B. An arete is a narrow, sharp-crested ridge formed by glacial erosion. It commonly develops between two cirques or between adjacent glacial valleys. Ice erodes the rock on both sides of the intervening ridge by abrasion and plucking. As erosion continues from both directions, the ridge becomes steep, narrow, and knife-edged. Option A is a coastal depositional feature formed from sand. Option C is a broad, flat surface built mainly by river deposition during floods. Option D is a wind-deposited mound of sand. None of those has the characteristic sharp, glacially carved ridge form. Remember: an arete is the sharp ridge left between areas of glacial erosion.

Direct answer: B, limestone. Karst is a group of landforms produced mainly by the solution of soluble rock by groundwater. Limestone contains calcium carbonate, which can dissolve slowly when rainwater absorbs carbon dioxide from the air and soil and becomes weakly acidic. As this water enters cracks, joints, and bedding planes, it enlarges them and may create caves, sinkholes, underground drainage passages, disappearing streams, and springs. A, granite, is a hard crystalline rock and is generally much less soluble, so it does not commonly develop classic solution caves. C, coal, is an organic sedimentary rock and is not the usual bedrock for karst landscapes. D, volcanic glass, is formed from rapidly cooled lava and is not the characteristic soluble rock required here. A useful memory cue is: karst means water dissolving limestone. Do not confuse karst erosion with ordinary river erosion; the essential process is chemical solution by groundwater.

Direct answer: A, mushroom rock. A mushroom rock, also called a rock pedestal in many school-geography contexts, forms when wind-blown sand abrades an exposed rock. Sand grains are usually carried most effectively close to the ground, so the lower part may be worn more strongly than the upper part. With repeated abrasion, the base becomes narrower while the top remains broader, giving the rock an umbrella-like or mushroom-like shape. A is correct because it names this wind-erosional landform. B is wrong because a drumlin is a streamlined hill associated with glacial ice and glacial deposits, not wind abrasion. C is wrong because a delta forms through river deposition near a river mouth. D is wrong because a spit is a narrow ridge of coastal sediment built mainly by longshore drift. The exact shape of a mushroom rock can vary with rock hardness, jointing, wind direction, and the amount of sand available. Memory cue: sand-laden wind attacks the lower part, leaving a broad cap over a narrow base.

Direct answer: A, barchan. A barchan is a crescent-shaped sand dune. It commonly develops where the wind blows mainly from one prevailing direction, the ground is relatively firm, and the supply of sand is limited. Wind pushes sand up the gentler windward slope. After the grains pass over the crest, they fall down the steeper sheltered slip face. The two pointed horns generally extend in the downwind direction, although their exact shape depends on wind strength, surface roughness, and the amount of sand. A is correct because barchan specifically names this crescent dune. B is wrong because a moraine is sediment transported or deposited by a glacier. C is wrong because a lagoon is a shallow water body partly separated from the sea, often by a barrier. D is wrong because a sea cliff is a steep coastal slope produced mainly by wave erosion. Memory cue: ‘bar-khan’ can be linked with a crescent-shaped desert dune; do not confuse it with a moraine, which is glacial, or a lagoon, which is aquatic.

The direct answer is A: yardang. In an arid region, wind carries sand that acts like a natural abrasive tool. Softer rock is worn away more quickly, while harder rock resists erosion for a longer time. This unequal removal is called differential erosion. The resistant material left behind becomes a long, narrow, streamlined ridge known as a yardang. Yardangs are commonly shaped in the general direction of prevailing winds. B, a zeugen, is also a wind-eroded feature associated with layers of hard and soft rock, but it is usually described as a more tabular or grooved form beneath a resistant cap, not the best match for the simple definition of a long streamlined ridge. C, a mushroom rock has a broad top and narrow base because sand abrasion is strongest near ground level. D, a ventifact is one wind-shaped stone, not a large ridge. Thus A fits both the size and formation described. Memory cue: a yardang is a “wind-carved yardstick” or long ridge.

The governing concept is that velocity is greatest along the outer bank of a meander because the current is pushed toward that side. Greater velocity and hydraulic force remove soil and rock through lateral erosion, producing a steep cut bank. Deposition mainly occurs on the slower inner bend, while glacial abrasion and wind deflation are unrelated agents.

A retreating waterfall erodes the resistant and softer layers around its plunge pool, gradually moving upstream. Repeated undercutting and collapse leave behind a long, narrow, and deep valley with steep sides, known as a gorge. A lagoon is coastal, a barchan is a crescent-shaped sand dune, and loess is wind-deposited silt, so none fits the river process.

The governing process is fluvial abrasion, also called corrasion. Pebbles carried by turbulent water become trapped in small depressions and rotate repeatedly, drilling and polishing the bedrock. Over time they enlarge the depressions into rounded potholes. Deflation is wind removal, while marine and glacial deposition add sediment rather than excavating circular holes in a river bed.

The governing concept is glacial erosion. An arete is a sharp ridge left between two cirques or glacial valleys, whereas a horn is a pointed peak carved by glaciers eroding several sides of a mountain. Although their shapes differ, both result from the cutting action of moving ice. River, wind, and groundwater deposition are depositional processes and cannot explain these sharp erosional forms, so D is correct.

The direct answer is A. A hanging valley is a smaller tributary valley whose floor remains higher than the floor of a deeper main valley. This difference usually develops through glacial erosion. A large, powerful main glacier cuts its valley deeply and broadly, while a smaller tributary glacier removes less rock. After the ice melts, the tributary valley appears to hang above the main valley, leaving a steep step at its junction. The tributary stream must descend this step, so a waterfall or cascade commonly forms. A is correct because it states the essential height difference. B is wrong because sinking into the sea is not the defining reason for a hanging valley. C is wrong because sand dunes are wind-deposited features and do not produce the characteristic glacial step. D is wrong because a blocked river mouth does not explain why the tributary valley floor is elevated above the main valley. Memory cue: main glacier cuts deeper, tributary joins from above, water falls at the step.

Direct answer: C is correct. Both landforms are glaciofluvial, meaning that they are produced by meltwater associated with glaciers. An esker is a long, winding ridge, usually made of sand and gravel deposited by a meltwater stream flowing through or beneath glacier ice. An outwash plain is a broad, gently sloping spread of sand and gravel deposited by meltwater beyond the glacier front. Their shapes are different: one is a ridge and the other is a plain, but their common agent is flowing glacial meltwater. A is wrong because sea waves are marine agents, not the defining agent here. B is wrong because wind erosion is aeolian, not glaciofluvial. D is wrong because limestone solution produces karst features. Memory cue: “meltwater makes both”—a winding esker and a spreading outwash plain.

The governing concept is a kettle-lake depression formed by melting stagnant ice. During glacial retreat, blocks of glacier ice may become buried by sand and gravel. When a buried block later melts, the overlying sediment collapses or settles, leaving a hollow. Rainwater or groundwater can then fill that hollow to create a kettle lake. Coastal bars, meander cutoffs, and desert deflation are different processes, so A is correct.

A is correct. Deflation is the removal and transport of loose particles by wind. Abrasion is the wearing of rock when wind-driven sand and dust strike its surface. Thus, deflation removes material, while abrasion wears exposed rock.

C is correct. Loess is a widespread, blanket-like deposit made mainly of fine wind-blown silt and dust. A sand dune is usually a distinct mound or ridge made of comparatively coarser sand. Thus, loess differs in both its finer material and its broad spread.

The governing concept is differential wind erosion. In a yardang field, persistent winds carrying dust and sand remove softer or weaker rock more rapidly, while harder bands resist abrasion and remain standing as elongated ridges. The contrast between eroded grooves and surviving ridges creates the streamlined yardang pattern. Therefore A is correct; melting, wave deposition, and selective river dissolution are unrelated processes.

A ventifact is a stone shaped, polished, or faceted by the impact of wind-blown sand. Its polished faces, grooves, and angular facets can indicate that strong abrasive winds acted on the exposed surface; where the facets are oriented, they may also help infer the prevailing wind direction. Hence B is correct. Limestone deposition, glacial meltwater, and river floodplains do not produce this characteristic wind-polished evidence.

The governing concept is coastal erosion and cliff retreat. Repeated wave attack is concentrated at the foot of a sea cliff, where hydraulic action and abrasion cut a notch. The weakened cliff collapses and retreats landward, leaving behind a broad, gently sloping rocky surface at the former cliff base: the wave-cut platform. Thus B is correct; the other options describe glacial, river-mouth, or groundwater deposition rather than marine erosion.

A is correct. Longshore drift moves beach sediment along the coast as waves approach at an angle. Where the water loses energy, the sediment is deposited. Repeated deposition can build a long, narrow ridge extending from the coast, called a spit.

The governing concept is coastal deposition and partial isolation of water. A bar is a ridge or bank of deposited sand or shingle that develops across or near a coastal inlet. If it closes the opening sufficiently, water behind it becomes separated from the open sea while remaining shallow, forming a lagoon. Thus A is correct. The other options incorrectly assign glacial, fluvial, or wind actions to a coastal depositional feature.

The governing concept is coastal depositional morphology. A tombolo is a depositional ridge that links an island to the mainland or to another island. A spit is a ridge attached to the coast at one end that projects into the sea, an estuary, or a bay, often shaped by longshore drift. Therefore A states the key difference. Both are commonly coastal deposits, so the glacial, wind, cave, river-bed, and groundwater claims are incorrect.

The governing concept is that geomorphic erosion depends on the agent and its movement. A river cuts, transports, and sometimes deposits material through flowing water, while a glacier erodes bedrock through the movement of thick ice, including abrasion and plucking. Both agents can also deposit sediments, so erosion is not their only action; however, option B correctly identifies the medium responsible for their erosional work.

The governing concept is deposition, in which a transporting agent loses energy and drops its sediment load. At a river mouth, slowing water deposits silt, sand, and clay to build a delta. Along a beach, waves and currents deposit sand or gravel where transport energy decreases. Erosion removes material, plucking is mainly associated with glaciers, and solution dissolves soluble rock, so B is the only common process.

The governing concept is classification by the dominant geomorphic process. A gorge is a deep, narrow valley commonly cut by a river, whereas a cirque is a bowl-shaped hollow excavated by glacial ice near a mountain head. Their agents differ—running water and moving ice—but both remove and wear away rock, so both are erosional landforms. They are not depositional, wind-made, or marine forms; therefore C is correct.

The governing concept is depositional landform identification by both process and agent. A moraine is an accumulation of rock debris carried and released by glacial ice. Loess is a blanket of fine wind-blown silt deposited over land. In contrast, a cirque, sea cave, yardang, sinkhole, and waterfall are primarily erosional or solution-related forms. Thus only the moraine–loess pair contains two depositional landforms, making B correct.