Erosional and depositional landforms created by various agents

Wave refraction occurs when waves enter shallow water at different angles and their speed changes. Wave fronts bend toward the headland, concentrating wave energy there, while energy is reduced in the adjoining bay. The concentrated impact increases hydraulic action and abrasion, so the headland erodes more rapidly. Therefore, option A is correct; the other choices describe unrelated depositional, glacial, or wind processes.

The correct answer is B, a wave-cut notch. Waves repeatedly erode a weak part of the cliff’s base through processes such as hydraulic action and abrasion, forming a hollow. As the notch deepens, the rock above may lose support and collapse, allowing the cliff to retreat landward.

The correct answer is C. A wind gap is a dry passage or valley that was once occupied by a stream. It may remain after river capture diverts the stream into another drainage system, or after an older valley is abandoned. Marine-bar deposition, glacial plucking, and loess deposition do not explain this former river route.

Direct answer: B, the sudden bend of a stream after river capture. A capture elbow is a noticeable angular bend in a drainage network. The sequence is important: a river erodes headward, reaches another stream, and diverts that stream into its own channel. Because the captured stream must change direction abruptly, a sharp elbow appears at or near the capture point. A is wrong because a tombolo is a depositional coastal bar joining an island to the mainland or another island. C is wrong because a moraine is sediment deposited by glacial ice. D is wrong because a karst column develops in a limestone cave when a stalactite and stalagmite join. Memory cue: “capture changes flow direction; the bend is the elbow.”

A is correct. River terraces are remnants of former valley floors left above the present river channel. If erosion leaves corresponding terrace remnants at similar heights on both sides of a valley, they are paired; if the remnants do not correspond across the valley, they are unpaired. This distinction reflects the symmetry or asymmetry of river erosion and valley development. Sea tides, cave length, and loess thickness do not classify river terraces.

Glacial plucking occurs when meltwater enters joints and cracks in bedrock, freezes, and helps loosen blocks. As the glacier moves, basal ice grips and removes these loosened blocks, producing erosion. Therefore option A correctly describes the required freeze–thaw weakening followed by ice removal; the other options are coastal, riverine, or wind-deposition processes.

An esker is a sinuous or elongate ridge deposited by meltwater streams flowing in or beneath glacial ice. A drumlin is an oval, streamlined hill made mainly of till and shaped beneath moving ice. Thus option B correctly distinguishes their material and formation, while the other choices incorrectly assign both forms to coasts, rivers, or waves.

A glacier can erode and overdeepen weak zones in its bed, especially through abrasion and plucking. When the ice retreats, water occupies the resulting hollow in solid bedrock and forms a rock-basin lake. Option C is therefore correct. Loess and delta formation are depositional processes, while a sea cave is a coastal erosional feature rather than a glacial rock basin.

In arid and semi-arid regions, weathering and runoff gradually widen individual pediments at the foot of uplands. Continued backwearing causes neighbouring pediments to merge, creating a broad, gently sloping erosional surface called a pediplain. Option A expresses this process. Coral, eskers, and cave columns are unrelated depositional or glacial-karst features.

A is correct. Floods deposit relatively coarse sediment near the river channel, gradually building natural levees. The area behind a levee is often lower and poorly drained, so floodwater and fine sediment can collect there. This waterlogged, marshy area is called a backswamp.

A is correct. During high flow, a river may cut through the low inner part of a meander and create a shorter channel across the bend. This is a chute cutoff. It differs from a neck cutoff, which cuts through the narrow strip of land between two approaching parts of a meander.

A is correct. A narrow, deep gorge forms when a river cuts downward into its bed faster than it erodes sideways. This makes vertical incision greater than lateral widening. Deposition, coastal wave action, and glacial till deposition do not explain the formation of a river-cut gorge.

A is correct. A low-gradient river may not have enough energy to carry all its sediment load, so some sediment is deposited as bars within the channel. The flow divides around these bars into multiple shifting channels, creating a braided pattern. The other landforms are associated with coastal waves, glaciers, and cave deposits, respectively.

Travertine is a chemical limestone deposit formed when calcium-carbonate-rich groundwater or spring water loses carbon dioxide, commonly because of turbulence, pressure release, temperature change, or evaporation. Calcite then precipitates around springs, channels, or waterfalls. Wind abrasion, glacial till compaction, and river incision are erosional or mechanical processes and do not form travertine.

A is correct. Karst commonly develops in soluble rock such as limestone, where joints and passages can be enlarged by dissolution. A stream may flow into a swallow hole, or ponor, and continue underground. The water has not vanished; it may later emerge at a spring.

Yardangs and zeugen are wind-eroded desert landforms, so the governing process is aeolian erosion, especially abrasion and differential erosion. Wind-blown sand attacks exposed surfaces, while harder layers resist erosion longer than softer or less-protected material. This unequal rate produces streamlined ridges or irregular rock forms, making option A correct. Calcite deposition, river levees, and glacial cirques are produced by different agents.

A is correct. A ventifact is shaped by abrasion from wind-blown sand. When winds from different directions expose different sides of a rock to sand-blasting, repeated abrasion can produce several flat facets. The other options do not describe the characteristic wind action that forms a ventifact.

A is correct. During intense desert rain, runoff may spread in a shallow sheet across a pediment rather than staying in one channel. This flow carries weathered material, erodes parts of the slope, and deposits sediment where the water loses speed.

The distinction depends on dominant process and material. A bajada forms when neighbouring alluvial fans spread from mountain valleys and merge into a broad apron of deposited sediment. A pediment is mainly a gently sloping, bedrock surface cut by erosion at the mountain front, although a thin sediment cover may occur. Therefore option A gives the correct contrast; the other options confuse desert forms with marine, karst, or glacial features.

A is correct. Star dunes form where winds blow from several directions and there is enough loose sand. These changing winds build intersecting ridges around a central peak. With a continued supply of sand, deposition can build the dune upward as well as outward, allowing it to become very high.

A spit is a depositional ridge of sand or shingle built by longshore drift. If its growing end extends across most of a bay entrance, the enclosed water becomes separated from direct marine circulation. Fine sediment and organic material may then accumulate in the sheltered, shallow water, forming a lagoon behind the spit or bar. Thus option A is correct; the other options describe impossible or unrelated landform processes.

A is correct. A ria forms when the sea floods a former river valley. A fjord forms when the sea floods a valley carved and deepened by a glacier. Their difference is the process that formed the valley before it was submerged.

A is correct. Waves keep eroding an isolated sea stack, especially near its base. As the rock is worn down, the tall stack becomes a low remnant called a stump. A moraine is glacial debris, a delta forms from river sediment, and loess is wind-deposited silt.

A is correct. Attrition is the wear that occurs when transported particles collide with one another, often becoming smaller and rounder. Corrasion, also called abrasion, occurs when moving particles scrape or strike a surface such as a river bed or coast. Thus, attrition is particle-on-particle wear; corrasion is particle-on-surface erosion.

A is correct. Waves push water and air into joints and cracks in a coastal cliff. Repeated changes in pressure weaken the rock, and waves can remove loosened fragments. A crack in a weak zone may gradually widen and deepen into a sea cave. Loess is wind-deposited sediment, till is glacial debris, and drumlins are glacial landforms.