Erosional and depositional landforms created by various agents

The governing concept is glacial deposition, in which a glacier leaves behind rock fragments, clay, sand, and other debris as it moves or melts. A moraine is a ridge or accumulation of this glacial debris, so option A is correct. A sea cave is produced by waves, a yardang by wind erosion, and a pothole by turbulent river abrasion. These distractors belong to other geomorphic processes.

The governing concept is coastal deposition caused by longshore transport and the settling of sediment. A spit is a narrow ridge of sand or shingle attached to the coast at one end and built outward by deposited material, so option B is correct. A wave-cut platform, sea cave, and stack are primarily erosional features produced by wave attack on coastal rock. Their common coastal setting does not make them depositional.

The governing concept is deposition by mineral-rich groundwater in a limestone cave. As water drips from the roof, evaporation and loss of carbon dioxide cause calcium carbonate to precipitate and build a hanging projection called a stalactite. Therefore, option A is correct. A drumlin is associated with glacial deposition, while a yardang and gorge are mainly erosional forms made by wind and running water respectively.

The governing concept is aeolian erosion and deposition. A yardang is a streamlined ridge or rocky projection carved when wind-driven sand abrades and removes softer material, so option B is correct. Loess is fine sediment deposited by wind, while a delta forms from river deposition and a natural levee develops from flood-borne sediment along a river bank. Thus only the yardang is erosional and wind-shaped.

The river is the correct agent because it both erodes and deposits transported sediment. Near its mouth, reduced speed causes sand and silt to accumulate into a delta; during floods, overbank deposition builds a floodplain beside the channel. Wind may form dunes, glaciers form moraines, and groundwater forms karst features, so those alternatives do not explain both landforms.

A glacier is the correct agent because it produces both erosional and depositional landforms. Plucking and abrasion by moving ice excavate a bowl-shaped cirque, usually near the head of a glacial valley. Rock debris carried and deposited by ice forms a moraine. Sea waves, groundwater and wind can create other features, but not this characteristic pair.

Groundwater is the correct agent in limestone regions. Slightly acidic water enters cracks, dissolves calcium carbonate and enlarges underground passages into caves. When mineral-rich water drips from a cave roof, some water evaporates and calcium carbonate is deposited, gradually building a stalactite downward. Wind, river ice and storms do not normally create this connected karst pair.

Wind is the correct agent because it can erode exposed rock and deposit loose sediment. Sand carried close to the ground abrades the lower part of a rock more strongly, producing a narrow base and wider top called a mushroom rock. Where wind loses speed, it deposits sand and builds dunes. Glaciers, waves and groundwater form different characteristic landforms.

Sea waves are the correct agent because coastal waves perform both erosion and deposition. Hydraulic pressure and abrasion attack weaknesses in a rocky cliff and enlarge them into a sea cave. In sheltered areas or where wave energy decreases, sand, pebbles and shell fragments are deposited to form a beach. Rivers, glaciers and groundwater may shape other environments but do not best explain this pair.

Option A states the fundamental distinction. Erosion is the wearing away and removal of soil or rock by agents such as running water, wind, ice or waves. Deposition occurs when the transporting agent loses energy and lays the sediment down. Therefore erosion generally lowers or relocates material, while deposition accumulates it; the other statements incorrectly restrict or deny these processes.

Option B is correct because a U-shaped valley is a classic product of glacial erosion. A valley glacier widens and deepens an earlier river valley through abrasion and plucking, creating broad sides and a relatively flat floor. Deltas are mainly fluvial deposits, barchans are wind-built dunes, and stalactites form through groundwater in caves, so the other pairings mismatch the agents.

A meander is the correct answer. In a river bend, the faster current usually erodes the outer bank laterally, while slower water on the inner bank deposits sediment. Repeated bank erosion and deposition enlarge the bend into a winding meander. A cirque and moraine are glacial features, whereas a stalactite is a groundwater-depositional cave feature, so they are unsuitable distractors.

A hanging valley is generally associated with glaciers. A smaller tributary glacier erodes its valley less deeply than a larger main glacier, so after the ice retreats, the tributary valley floor remains high above the main U-shaped valley. This difference in glacial erosion creates the hanging appearance, often with a waterfall at the junction. Rivers, wind and groundwater do not normally produce this classic feature.

Option A correctly defines a tombolo. It is a depositional coastal ridge or bar made mainly of sand, gravel or shingle that connects an offshore island with the mainland or another island. Wave refraction and sheltered water can reduce wave energy, allowing sediment to accumulate along the connecting route. The other choices describe glacial, fluvial or aeolian features, not a tombolo.

A gorge is a narrow, deep valley produced mainly by strong vertical erosion by a river, especially where the river cuts downward through resistant rock or a steep landscape. Therefore, option A is correct. A sea arch is carved by waves, a sand dune is deposited by wind, and a moraine is material deposited by a glacier; none is a river-cut gorge.

A waterfall is primarily a river erosional landform. It commonly develops where a river flows over alternating hard and soft rock: the softer rock is worn away faster, creating a step, while continued erosion causes the water to fall over the harder ledge. Thus option A is correct. The other choices describe depositional processes by glaciers, wind, or marine agents.

Large, looping bends in a river channel across a flat plain are called meanders, so option A is correct. They develop when lateral erosion acts on the outer bank of a bend while slower water deposits sediment along the inner bank. A horn is a sharp glacial peak, a yardang is wind-eroded bedrock, and a pillar is not the standard term for a river bend.

A natural levee is a raised embankment along a river channel formed when floodwater spreads over the banks and quickly loses velocity. The heavier sand and silt settle close to the channel, gradually building the bank higher. Therefore, option A is correct. A cirque is glacial, a sea stack is produced by wave erosion, and a mushroom rock is shaped mainly by wind abrasion.

A floodplain is the broad, relatively flat area beside a river that is periodically covered by floodwater. Repeated flooding spreads and deposits layers of fine alluvium, gradually building this plain. Therefore, option A is correct. A gorge is a narrow erosional valley, a wave-cut platform is formed by coastal waves, and an arete is a sharp ridge created by glacial erosion.

A U-shaped valley is produced by glacial erosion. Moving ice occupies an earlier valley, removes rock from the floor, and widens and steepens the sides through abrasion and plucking. This changes a narrower V-shaped valley into a broad U-shaped one, so option A is correct. River deposition, wind deposition, and marine deposition add sediments rather than excavating a U-shaped glacial valley.

A cirque is a bowl-shaped, steep-sided hollow carved by glacial erosion near the head of a glacier. Freeze-thaw action and the movement of ice deepen and widen the hollow. Therefore, option A is correct. A delta forms where a river deposits sediment, a sand dune is made by wind, and a natural levee is a raised river-bank deposit.

Deflation is the wind-erosion process in which moving air lifts or carries away loose, fine particles such as dust and sand from an exposed surface. It may lower the ground or leave coarser stones behind. Therefore, option A is correct. Glaciation is the action of ice, tidal deposition adds sediment through tides, and chemical precipitation forms minerals from a solution.

The correct answer is Sand dune. Wind transports loose sand and deposits it where wind speed decreases or an obstacle interrupts movement. Repeated accumulation creates a mound or ridge called a dune, a common depositional landform of deserts. A gorge is a deep river-cut valley, a cirque is a bowl-shaped glacial hollow, and a sinkhole is a depression formed by collapse or dissolution, so none of them fits the description.

Direct answer: A, loess. Loess is a blanket-like deposit made mainly of very fine wind-blown silt and dust. First, wind lifts and transports tiny, dry particles. When the wind loses speed, the particles settle over the ground and may form thick, fairly widespread layers. The key clues are “fine dust,” “carried by wind,” and “deposit.” Loess is therefore an aeolian, or wind-made, depositional landform. A is correct because it names this fine wind-deposited material. B is incorrect because an esker is a winding ridge of sand and gravel deposited by meltwater flowing through or beneath glacial ice. C is incorrect because a natural levee forms beside a river when floodwater deposits coarser sediment along the channel banks. D is incorrect because a sea stack is an isolated coastal rock left after waves erode surrounding rock. Memory cue: fine wind-blown dust forming a broad blanket equals loess.

The correct answer is Yardang. A yardang is a streamlined, elongated ridge carved in bedrock by persistent wind abrasion and deflation, especially where alternating hard and soft layers allow unequal erosion. The softer material is removed faster, leaving sharp ridges aligned broadly with the prevailing wind. A delta and beach are depositional features, while a cirque is a bowl-shaped hollow formed by glacial erosion.