Erosional and depositional landforms created by various agents

A sea arch is produced when waves exploit cracks and weak zones in a coastal cliff. Hydraulic action and abrasion enlarge caves until erosion cuts through the headland, leaving an arch. Therefore option D correctly matches the agent and landform. Cirques are carved by glaciers, beaches are mainly depositional coastal forms, and stalactites grow from mineral deposition in caves, so the other pairs are incorrect.

The direct answer is A. An inselberg is an isolated, steep-sided hill or rock mass that rises above a comparatively level surface, especially in arid and semi-arid regions. The surrounding rocks are weaker and are removed more rapidly by weathering and erosion, while the more resistant rock remains standing. This is why it is called a residual landform. B is wrong because a sandy beach is a coastal depositional feature made by waves and currents. C is wrong because a glacial deposit is formed by deposition, not by the survival of a resistant rock mass. D is wrong because distributaries are channels in a delta. Memory cue: an inselberg is a resistant “island” of rock left behind after surrounding land is worn down.

The direct answer is C. A tombolo is a narrow depositional ridge, usually made of sand or gravel, that joins an island to the mainland or sometimes joins two islands. Waves bend, or refract, around the island, and wave energy becomes lower in the sheltered water behind it. Longshore drift carries sediment into this lower-energy zone, where the material accumulates until a connecting bar develops. A is wrong because a drowned glacial valley is associated with a fjord. B describes river erosion, not coastal deposition. D is wrong because wind does not normally dissolve limestone; solution is mainly a chemical process involving water. Memory cue: tombolo is a sediment “bridge” from island to land.

The governing concept is fluvial erosion. A canyon is a very deep, narrow valley with steep sides, produced mainly when a river cuts vertically downward through resistant rock. Arid or semi-arid conditions often preserve the steep walls because weathering and vegetation are limited. Therefore, option A is correct. Options B and D describe deposition, while C is a glacial landform process, not river downcutting.

The correct answer is C. A peneplain is a broad, low-relief surface formed as prolonged erosion and denudation wear down an older landscape toward a nearly level surface. It develops over a long period, not through a single sudden event.

The governing concept is erosion by running water. During intense surface runoff, small channels deepen and widen into gullies, especially on soft, dry, sparsely vegetated soil. Continued dissection can produce a highly uneven landscape of ridges, ravines, and narrow channels known as badland topography, so option A is correct. A sea arch is wave-eroded, a drumlin is glacial, and a loess plain is formed mainly by wind-deposited silt.

The correct answer is C. Incised or entrenched meanders are deep valleys that preserve the bends of an older river course. If uplift or a fall in base level renews a river’s downward erosion, the river can cut deeply while continuing to follow those bends. The meander pattern is therefore preserved in the valley walls.

The correct answer is D. A fall line marks a zone where rivers descend from a higher, more resistant upland toward a lower plain, often where relief or rock resistance changes. The change in gradient can create rapids or waterfalls. The other choices describe desert, cave, or marine features rather than this river-landscape setting.

The governing concept is glacial erosion. An arête is a narrow, sharp-edged ridge left between two adjacent cirques or glacial valleys when ice erodes the mountain from both sides. Continued erosion may make the ridge knife-edged, so option B is correct. A rounded mound would be a different depositional feature, while a crescent dune is formed by wind and a coastal plain by marine processes; none of these is an arête.

A roche moutonnée is shaped beneath moving glacier ice. Abrasion by rocks frozen into the glacier smooths and polishes the gently sloping stoss side facing the ice flow. On the steeper lee side, pressure release and wedging allow the glacier to pluck blocks from the bedrock, making that side rough. Therefore, option C correctly identifies both processes; the other choices describe marine, fluvial, or aeolian actions.

A wave-cut notch is a recess carved into the lower part of a sea cliff, usually close to the average water level. Waves attack weaknesses through hydraulic pressure, abrasion and the impact of transported sediment. Continued undercutting makes the cliff unstable and promotes retreat, often leading later to a wave-cut platform. Since the other options describe glacial, aeolian or cave processes, A is correct.

Correct answer: C. Weak, jointed rock is easier to erode, and powerful waves can widen its cracks and cut into the cliff’s base. As the base is undercut, the overhanging rock may collapse, moving the cliff inland. Hard, uncracked rock and low-energy or absent waves slow this process.

An uvala is a relatively large, irregular karst depression produced when two or more neighbouring dolines expand and merge. It is therefore larger and more complex than an individual doline, although its floor may contain smaller solution features. A crescent dune is aeolian, a coastal stack is marine, and outer-bend erosion is fluvial; none represents an uvala. Thus, A is correct.

C is correct. Both are depositional landforms commonly formed where a stream leaves a steeper valley and reaches gentler ground. Its reduced speed and carrying capacity cause sediment to accumulate and spread near the valley mouth. An alluvial cone is generally steeper than an alluvial fan, but both form through stream deposition as the slope decreases.

C is correct. A bird-foot delta forms when river deposition is stronger than the waves and currents that would otherwise redistribute or remove sediment. The river divides into long, narrow distributaries that extend into the receiving water, creating a shape reminiscent of a bird’s toes. If waves removed all the sediment, a delta would not build outward.

D is correct. Estuaries are affected by tides and coastal currents, which can resuspend and carry sediment away from the river mouth. In a delta, river-borne sediment can accumulate when deposition exceeds the removal of material by waves and currents. This is a general tendency, not a rule for every estuary or delta.

Planation, or the lowering and smoothing of relief, commonly depends on a linked sequence of processes. Weathering breaks down and weakens rock in place, making particles easier to detach, while erosion by running water, wind, ice, or waves removes and transports that material. Repeated weathering and erosion gradually reduce uneven relief. Option A is correct; the other statements deny the essential roles of these processes.

D is correct. A river’s carrying capacity is the amount of sediment it can transport. When its flow loses energy, for example as its velocity decreases, it can no longer carry as much material, so some sediment is deposited. Coarser particles generally settle before finer ones. A decrease in carrying capacity does not by itself straighten meanders or form a glacial valley.

The correct answer is B. Saltation is the movement of sediment in short hops or bounces. Wind can carry sand grains this way, and flowing water can move sand or small pebbles in a similar manner along a river bed. Coral and cave calcite are materials or deposits, not transporting agents; a stationary snow peak does not transport sediment.

Glaciers erode landscapes mainly through plucking and abrasion. As a valley glacier moves, it widens and deepens a pre-existing river valley, producing the broad, steep-sided U-shaped valley. A sea cave is an erosional coastal feature rather than a depositional one; barchans are wind-deposited dunes, not solution landforms; and deltas form by river deposition. Thus option C is the correct process–landform pair.

The governing concept is fluvial erosion during the youthful or upper course of a river. A steep gradient gives the river high energy, so downward or vertical erosion is stronger than sideways erosion. Continued downcutting produces a narrow, deep valley with steep walls, called a gorge. Lateral erosion in plains forms wider valleys, while deposition at the mouth produces features such as deltas, not gorges.

A canyon is commonly wider because its valley sides are enlarged by weathering, mass movement, and sideward erosion in addition to river downcutting. In many arid regions, strong temperature changes weaken exposed rock, while the river deepens the channel. A gorge is generally narrower and more confined. Glacial deposition, permanent sea-wave action, and delta formation are not the defining processes here.

The correct answer is C. As a waterfall retreats upstream through repeated erosion and collapse of rock, it can leave behind a narrow, deep valley with steep sides called a gorge. A sea arch is formed by coastal wave erosion, a barchan is a wind-shaped sand dune, and a drumlin is a glacial landform.

In a meander, the flow follows a curved path and its highest velocity is usually directed toward the outer bank. The centrifugal effect and helicoidal circulation concentrate stream energy there, increasing hydraulic action and abrasion. The outer bank therefore becomes a cut bank through lateral erosion. Flow is slower on the inner bank, where sand and silt are deposited to form a point bar, so option A is correct.

A point bar is a depositional feature on the inner curve of a meander. Water moving around the inner bank has lower velocity and reduced transporting capacity, so sand, silt, and small gravel settle there. At the same time, the faster outer-bank flow causes erosion and forms a cut bank. Wave corrosion, glacial plucking, and desert deflation involve other agents and do not explain this feature.