Erosional and depositional landforms created by various agents

Yardangs are streamlined ridges carved by persistent wind abrasion and deflation in dry regions. Where rock layers differ in hardness, softer material is removed more rapidly while resistant bands remain as elongated ridges aligned with the prevailing wind. Option A supplies both essential conditions. Forest moisture, glacial snowfall and tidal-coral processes belong to different environments and do not form yardangs.

Waves enlarge a coastal cave until it cuts through a headland and forms a sea arch. Continued undercutting weakens the arch roof; when the roof collapses, a resistant rock pillar may remain isolated from the cliff as a sea stack. Therefore option D correctly describes the sequence. Sand deposition, coral growth and delta extension are depositional or biological processes, not the direct cause of a stack.

In a limestone karst region, acidic groundwater dissolves rock and may enlarge an underground cavity until the surface collapses, producing a sinkhole. In contrast, mineral-rich water dripping from a cave roof loses carbon dioxide and deposits calcite, gradually building a stalactite downward. Thus option B correctly contrasts solution and collapse with mineral deposition. The other choices assign both features to unrelated wind, glacial, river or marine processes.

Interlocking spurs develop in the upper, youthful course where the river has strong vertical erosion but limited lateral erosion. Because resistant ridges obstruct a straight route, the river winds around them, making alternating spurs appear to interlock. Therefore, option A is correct; lateral erosion, marine deposition, and glacial meltwater do not explain this characteristic river-valley form.

In a meander, water follows a curved path and its greatest velocity is directed toward the outer bank. The resulting centrifugal effect and concentrated flow increase hydraulic pressure and erosion there, producing a cut bank. The inner bank has slower flow and deposition, so option B is correct; the other choices describe the wrong process or location.

The correct answer is C: deposition of sand and silt due to lower velocity. In a meandering river, water generally moves more slowly and is shallower on the inner side of a bend. Lower velocity means lower carrying capacity, so the river can no longer transport all its sediment. Sand, gravel and silt are deposited there, forming a gently sloping point bar. A is wrong because wave cutting is a coastal process and attacks shores. B is wrong because glacial abrasion is caused by moving ice and rock fragments. D is wrong because solutional cave formation occurs when groundwater dissolves suitable rock. The inner-bank point bar contrasts with faster flow and erosion on the outer bank. Memory cue: “inside = slow and deposit; outside = fast and erode.”

The correct answer is B: strong tides and powerful marine currents at the mouth. A delta grows when a river deposits sediment at its mouth. Strong tides and currents can remove or redistribute that sediment, making it harder for a delta to build up. A supplies sediment, while calm coastal water and reduced river velocity generally encourage deposition.

The correct answer is D: river rejuvenation and renewed downcutting. A river terrace is an older floodplain or valley floor left above the present channel. When uplift or a fall in base level gives a river renewed energy, it cuts down into its former valley floor, leaving the old surface as a step beside the channel.

The correct answer is C: a deep valley or gorge. Falling water erodes the rock at the waterfall’s base, often undercutting softer rock beneath a harder layer. The unsupported rock above can then collapse, causing the waterfall to retreat upstream. Repeated erosion and collapse leave a deep, narrow gorge behind it.

A cirque is a steep-sided, bowl-shaped hollow at the head of a glacier. Snow accumulation, nivation, freeze-thaw action, plucking and abrasion progressively deepen and widen the hollow. Therefore, option D is correct. Wave deposition, river lateral erosion and wind suspension are processes associated with coasts, rivers or deserts, not the principal formation of a glacial cirque.

An arête is a narrow, sharp-crested ridge produced by glacial erosion. When two adjacent cirques or glacial valleys erode backward toward one another, the intervening rock is reduced to a knife-edge ridge. Thus option A is correct. Floodplain silt, coastal sand bars and groundwater limestone deposits are depositional features formed by different agents.

A horn is a steep, pyramidal mountain peak formed when three or more cirques erode a mountain from different sides. Continued headward erosion removes the surrounding rock and leaves a resistant central summit, often with sharp ridges radiating from it. Option B is therefore correct. A collapsed sea cave, a river delta and wind-deposited loess are unrelated coastal, fluvial and aeolian features.

A drumlin is a streamlined, elongated hill shaped beneath moving glacier ice, commonly composed of till. Its blunt end and tapered end, together with its long axis, record the direction in which the ice moved. Consequently, the long axis is generally parallel to glacier flow, making option D correct. Tides, prevailing winds and lateral river currents do not produce the characteristic streamlined glacial alignment of drumlins.

Lappies, also called limestone pavement or clint-and-grike topography, develop when slightly acidic rainwater dissolves exposed limestone. Water follows joints and bedding planes, enlarging them into deep grooves called grikes, while the intervening blocks are called clints. Therefore option C is correct. Wave abrasion, glacial plucking and river deposition are different processes and do not create this characteristic karst pavement.

Direct answer: B, limited sand supply and steady wind from one direction. A barchan is a crescent-shaped sand dune that develops where the available sand is not abundant and the wind usually blows from one dominant direction. The wind moves sand up the gentle windward slope and down the steeper slip face. Because the margins have less sand, the two horns extend downwind. A, dense vegetation and wet ground hold sand in place and reduce its movement. C concerns underwater currents, not an aeolian dune. D describes a glacial meltwater feature and has no role in forming a barchan. A useful warning is that abundant sand and changing wind directions tend to produce other dune forms, whereas limited sand and one dominant wind favour barchans.

An inselberg is an isolated residual hill that rises abruptly above a relatively level surrounding surface. It develops when weathering and erosion remove the weaker rocks around a more resistant mass. In many arid settings, the surrounding land is lowered toward a pediplain while the resistant core remains as an inselberg. Delta growth, oxbow formation, and cave calcite deposition are depositional or fluvial-karst processes with different results.

A tombolo is a depositional coastal bar that connects an offshore island with the mainland or, sometimes, with another island. Wave refraction around the island creates a zone of reduced wave energy behind it, encouraging sand and shingle to accumulate there. Continued deposition builds the connecting ridge. A sea-cave deposit, glacial debris, and an abandoned river bend describe different landforms and are not tombolos.

A lagoon is a shallow body of coastal water that is partly or nearly completely separated from the open sea by a sand bar, spit, barrier beach, or barrier island. Such barriers commonly develop through wave action and longshore drift, so option A is correct. A cirque is glacial, a V-shaped valley is produced by river erosion, and a desert hollow is associated with wind action rather than coastal enclosure.

A sea cliff and its basal notch are characteristic products of coastal wave erosion. Waves attack a zone of weakness at the foot of the cliff through hydraulic action, abrasion, and sometimes solution, cutting a notch. As the notch enlarges, the unsupported rock above collapses, causing the cliff line to retreat landward. Wind deposition, glacial deposition, and groundwater deposition do not normally form this paired coastal feature.

Badland topography develops where soft, easily eroded rocks are exposed to irregular but intense runoff, usually in areas with sparse vegetation. Because plant roots do not adequately bind the soil, rainwater rapidly cuts a dense network of rills and gullies, producing sharp ridges and narrow ravines. Option C is therefore correct. Dense vegetation protects the ground, while glacier deposition and coral formation are unrelated processes.

Answer: A. A pediment is a broad, gently sloping surface of exposed or thinly covered bedrock at the foot of a mountain, especially in an arid or semi-arid region. Weathering loosens material on the mountain front, while sheet wash and small streams carry some of it away. Repeated erosion gradually leaves a smooth rock-cut slope spreading outward from the mountain base. B is a delta, which is deposited where a river enters standing water. C is a sea stack, an isolated coastal rock left by marine erosion. D is a moraine, a ridge of sediment deposited by a glacier. Memory cue: pediment means a mountain-foot “paved” surface, not a deposit.

The correct answer is B. Streams flowing out from mountains deposit sediment in separate alluvial fans when they reach flatter ground and lose speed. When neighbouring fans spread and merge, they form a broad depositional apron called a bajada.

The correct answer is C: a salt flat or playa deposit. Water in a temporary desert lake can evaporate, leaving dissolved salts and fine sediment on the basin floor. A U-shaped valley is typically formed by glacial erosion, while a wave-cut platform and sea arch are coastal landforms shaped by waves.

The governing concept is the contrasting flow velocity across a river meander. Water moves fastest along the outer bank, causing lateral erosion and producing a cut bank or river cliff. Flow is slower along the inner bank, so sand and gravel are deposited there as a point bar. This paired erosion-and-deposition pattern identifies a meander system, making option D correct. Karst, coastal arches, and cirques do not have this paired fluvial arrangement.

Both bars and spits are coastal depositional features produced largely by sediment transport through waves and longshore currents. A spit is a narrow ridge attached to the mainland at one end and extending into a bay, estuary, or sea. A bar may extend across a bay or river mouth and partly or wholly block the water body, sometimes enclosing a lagoon. Thus option B states the key distinction.