Erosional and depositional landforms created by various agents

A gorge and a canyon are both deeply incised valleys produced mainly by prolonged river erosion, especially vertical downcutting. They differ in form and setting: a gorge is commonly narrower and steeper, while a canyon may be broader and bounded by layered rocks. Thus option A identifies their shared origin; the other options involve unrelated agents or processes.

A moraine is a depositional landform made of rock fragments, clay, sand and other debris transported and left behind by glacier ice. The material is commonly unsorted because ice carries particles of many sizes together. Terminal moraines form near a glacier’s snout, while lateral moraines occur along its margins. Thus option B is correct; erosion, marine action and groundwater solution describe different processes.

Deflation is the wind-driven removal, lifting and transport of loose, fine particles from an exposed desert surface. As sediment is progressively blown away, the ground may be lowered into a shallow or sometimes deep depression called a deflation hollow. Option B is correct. Glacial abrasion, coastal retreat and calcite deposition involve glaciers, waves and groundwater respectively, so they cannot explain this aeolian hollow.

The correct answer is A. Waves enlarge weak points in a headland to form a sea cave. Continued erosion may cut through the headland or join openings to create an arch. When erosion and weathering weaken the arch roof until it collapses, an isolated sea stack may remain. Thus the sequence is cave, arch, then stack.

The correct answer is B. Waves erode the base of a sea cliff, forming a notch. The overhanging rock may collapse, and continued erosion makes the cliff retreat inland. The rocky surface left at the foot of the retreating cliff is a wave-cut platform, often exposed at low tide.

The correct answer is C. Longshore drift transports sediment along the coast when waves approach it at an angle. Where the coast changes direction or the water becomes more sheltered, wave energy falls and sediment is deposited. Continued deposition can build a narrow ridge attached to the coast at one end: a spit.

The correct answer is B. Wind carries sand grains close to the ground, where they repeatedly abrade the lower part of an exposed rock. This wears the base away faster than the top, leaving a narrow base and a broader cap—the characteristic mushroom shape.

The correct answer is C. A misfit stream is much smaller than the valley it occupies. The valley was shaped when a larger river—or a greater volume of meltwater—flowed there, so the present stream appears undersized. A delta plain, polje, and sea arch are different landforms and do not describe this mismatch between stream and valley size.

A is correct. A tarn is a small lake occupying a cirque, a bowl-shaped hollow typically excavated by a glacier near the head of a valley. Water collects in the hollow after the ice retreats. A cut-off meander, by contrast, forms an oxbow lake.

Correct answer: B. A nunatak is a rocky peak or ridge that projects above the surrounding surface of an ice sheet or ice cap. Its summit remains exposed while the surrounding lower ground is covered by ice.

The correct answer is D. A uvala is a large, irregular closed depression in a limestone karst landscape. As slightly acidic water dissolves limestone, individual dolines can enlarge until the ridges between them disappear and the depressions merge. A river meander cutoff, a collapsed sea arch, and wind-deposited sand form different landforms, not a uvala.

The correct answer is B. Hums or pepinos are residual hills associated with karst landscapes. Solution lowers the surrounding soluble rock over time, leaving more resistant limestone patches standing as isolated hills. Floodplains, spits, and moraines are formed by river, coastal, and glacial processes, respectively.

The correct answer is C. A stalactite grows down from a cave roof, and a stalagmite grows up from the floor as calcium carbonate is deposited from mineral-bearing water. If the two formations eventually meet, they form a continuous calcite column from roof to floor. The other options describe wind, river, or coastal processes.

The correct answer is D. In a common process called deflation, wind removes loose dust, silt, and fine sand from a dry surface. Coarser pebbles are harder for the wind to move, so they remain and become concentrated into a closely packed stony cover called desert pavement. The other options describe glacial, tidal, or river-mouth processes.

The correct answer is C. Waves and storm water move sand and shingle and deposit it along the shore. Repeated deposition can build an elongated ridge of coastal sediment. River downcutting, cave collapse, and glacial scratching are different processes and do not form a beach ridge.

The correct answer is D. Waves and nearshore currents can carry sediment away from the beach and deposit it underwater in a long ridge, forming an offshore bar. A gorge, yardang, and cirque are landforms produced by river or wind erosion and glacial erosion, respectively.

Wave energy decreases in a sheltered bay, so waves lose the ability to transport all their sediment. Sand, pebbles, and other beach material are consequently deposited, often building a beach or a wider depositional shore. Option D is correct. Strong cliff erosion and cave collapse generally require energetic wave attack, while a lateral moraine is produced by glacial movement, not waves.

An esker is a ridge deposited by meltwater streams associated with a glacier, so the glacier-related pair in option A is the valid one. A delta is primarily deposited by running water, a barchan is a wind-shaped sand dune, and a drumlin is a subglacial landform. Hence options B, C, and D mismatch the agent with the landform.

The correct answer is A. Delta progradation is the outward, commonly seaward, advance of a delta when sediment builds up at its front. It occurs when sediment supplied by the river accumulates faster than waves, tides, and currents remove or redistribute it. As deposits extend outward, the delta shoreline advances. The other choices do not describe delta growth.

The correct answer is A. A recessional moraine forms at the edge of a retreating glacier when its front temporarily pauses. Debris carried by the ice accumulates at the margin during the pause and remains as a ridge when the glacier retreats again. The other options describe processes unrelated to moraine formation.

Correct answer: A. A nebkha is a small wind-formed mound. Vegetation or another obstacle slows the wind near the ground, causing transported sand to collect around it. Continued deposition builds the mound. The other options describe marine, glacial, or cave processes rather than wind deposition.

C is correct. Glacial plucking removes blocks from a glacier’s bed. Joints and cracks weaken the bedrock and provide surfaces along which blocks can be detached; the moving ice can then carry them away. Smooth, unjointed rock has fewer such weaknesses.

The correct answer is C. A wadi is usually a dry channel in an arid or semi-arid region, but intense rainfall can produce a short-lived flash flood. The fast-moving water erodes the channel and carries sediment; as it slows or spreads out, it deposits that material. Thus, a wadi can shape the landscape through both erosion and deposition.

The governing concept is that a tsunami is a long-wavelength sea wave produced by the sudden displacement of a large volume of seawater. The most usual trigger is an undersea earthquake, especially when movement of the ocean floor vertically raises or lowers the seabed and pushes the water column above it. The disturbance travels across the ocean and may grow much higher near a coast as the water becomes shallow. Therefore, option C is correct. Light wind usually produces ordinary surface waves, moonlight has no such force, and coastal sand cannot suddenly displace enough water. Volcanic eruptions or submarine landslides can also cause tsunamis, but they are less usual causes than undersea earthquakes.