Erosional and depositional landforms created by various agents

Correct answer: D. Undercutting at the base and collapse of rock

Correct answer: D, undercutting at the base followed by collapse of the overlying rock. A waterfall commonly develops where harder rock lies above softer rock or where rock layers have different resistance. Fast-flowing water and the impact of falling water erode the softer material at the base, creating a hollow or plunge pool. The unsupported upper rock then breaks and collapses. Repeated undercutting and collapse make the waterfall shift backward toward the source; this is called headward erosion or waterfall retreat. A is incorrect because delta deposition builds land at a river mouth. B is incorrect because loess is wind-blown sediment, not the main process shaping a retreating waterfall. C is a coastal depositional process and is unrelated. Memory cue: “Cut below, collapse above, retreat upstream.”

Correct answer: A. The youthful river stage dominated by vertical erosion

The governing concept is the youthful, upper-course development of a river valley. Strong vertical erosion produces a narrow V-shaped valley, while the river winds around projecting resistant ridges called spurs; the spurs appear to interlock when viewed downstream. Therefore option A is correct. Delta formation, wave deposition, and stalagmite growth belong to different environments and do not explain this valley pattern.

Correct answer: B. When a sand bar or barrier partly separates seawater

The governing concept is coastal deposition and partial enclosure. Longshore drift can build a sand bar, spit, or barrier island across part of a bay, separating shallow water from the open sea while sometimes leaving an inlet. The enclosed or semi-enclosed water body is a lagoon, so option B is correct. The other choices describe waterfall retreat, glacial processes, or fluvial meander cut-off.

Correct answer: C. When a stalactite and stalagmite join

The governing concept is solutional deposition in a limestone cave. Mineral-rich groundwater loses carbon dioxide and deposits calcium carbonate as a stalactite grows downward from the roof and a stalagmite grows upward from the floor. When the two deposits meet, they form a continuous column or pillar, making option C correct. The other options describe coastal, river, or unrelated erosional features.

Correct answer: C. By streams depositing sand and gravel within or beneath a glacier

An esker is a long, narrow, winding ridge composed mainly of sand and gravel. It forms when meltwater streams flow through tunnels within or beneath a glacier and deposit sediment as the flowing water loses energy. Therefore, option C correctly identifies a glaciofluvial depositional process. Coastal sand forms beaches or bars, floodplain silt is fluvial alluvium, and dripping cave water forms stalactites.

Correct answer: D. Glacial abrasion smooths the stoss side, while plucking roughens the lee side.

D is correct. A roche moutonnée is a bedrock knob shaped by moving glacier ice. Debris carried by the glacier abrades the stoss side, facing the approaching ice, and makes it smooth. On the lee side, ice can pluck blocks from joints in the bedrock, leaving a rougher surface. These contrasting processes explain the two slopes.

Correct answer: A. A very large closed depression with a flat floor.

A polje is a large, closed, usually elongated depression developed in soluble limestone terrain through solution, subsurface drainage, and related karst processes. Its floor may be relatively flat and can contain sediment or seasonal water. Option A is correct. A sea stack is coastal, a meltwater ridge is an esker, and a triangular river-mouth deposit is a delta; none is a polje.

Correct answer: A. Presence of joints, cracks and lines of weakness

Sea arches develop through concentrated marine erosion along weaknesses in coastal rock. Waves force water and compressed air into joints and cracks, while abrasion enlarges the opening into a sea cave. Continued erosion may cut the cave through the headland, producing an arch. Therefore option A is correct. Loose alluvial silt is not a stable arch-forming rock, and uniform crack-free rock lacks a focused weakness.

Correct answer: B. Meanders and point bars

Helicoidal flow is a corkscrew-like secondary current in a meandering river. Surface water moves toward the outer bank, while the returning near-bed current carries sediment toward the inner bank. This produces outer-bank erosion and inner-bank deposition, enlarging bends and building point bars. Consequently, option B is correct; the other choices are karst, wind, and marine landforms.

Correct answer: B. A strath terrace forms on a rock-cut surface, whereas a fill terrace forms in old alluvial fill

A strath terrace is a relatively flat bench cut into bedrock by a river and later left above the active channel after renewed incision. A fill terrace forms when a river cuts down into an older valley fill made of alluvium. Option B therefore identifies the key material difference: bedrock for strath and sedimentary fill for fill terraces; the other options assign unrelated origins.

Correct answer: A. A long-term adjustment between sediment load and the stream’s energy and transport capacity.

A is correct. A graded river has adjusted its slope and channel conditions over time so that its energy and transport capacity are broadly suited to its sediment load. This tends toward a long-term balance between erosion and deposition, although floods, uplift, or changes in sediment supply can disturb it and cause further adjustment.

Correct answer: A. Shifting of the main depositional area from one distributary to another

Delta lobe switching occurs when sediment deposition in one distributary becomes less effective because its channel is obstructed, its mouth becomes shallow, or another pathway offers lower resistance. Flow and sediment then shift toward a different distributary, building a new lobe while the former lobe receives less material. Thus A is correct; the other options incorrectly mix marine, glacial, aeolian, and karst landforms.

Correct answer: A. A long protected deposit of soft till forms behind a resistant rock crag

A crag and tail develops when moving glacier ice encounters a resistant bedrock knob. The knob forms the crag, while the rock shelters softer sediments on its down-ice side. These protected deposits are streamlined into a long tail. A sea stack results from marine erosion, loess is wind-blown silt, and a natural levee is deposited beside a river channel.

Correct answer: A. Small solution depressions merge into a larger irregular depression and may further form a very large flat closed basin

A doline is a relatively small closed depression produced mainly by limestone solution or collapse. Continued solution and the enlargement or joining of neighbouring dolines can create an irregular, larger depression called an uvala. Further enlargement may produce a broad, flat-floored, closed karst basin known as a polje. These are progressive karst forms, not marine, wind, or fluvial deposits.

Correct answer: A. Fine particles may have slight cementation and capillary bonding

Loess is a wind-deposited sediment dominated by silt-sized particles. Although it is loose and porous, dry loess can retain steep or nearly vertical faces because particle interlocking, weak carbonate or mineral cementation, and capillary forces provide limited cohesion. Moistening may destroy that apparent stability and cause collapse. Therefore option A is correct; loess is not made of boulders, coral, or solid glacial ice.

Correct answer: A. Deflation removes loose particles by wind, whereas abrasion wears rock surfaces with wind-borne sand

Deflation is the removal and lifting of loose dust, sand, and fine particles from the ground by wind. Abrasion, also called corrasion, occurs when wind-borne sand strikes and wears, polishes, or grooves exposed rock surfaces. Hence option A correctly distinguishes removal from wearing. Option B reverses the definitions, while options C and D incorrectly assign the processes to deposition, groundwater, rivers, or glaciers.

Correct answer: A. Wave energy becomes concentrated on the headland

Wave refraction occurs when waves enter shallow water at different depths around an irregular coastline. Near a projecting headland, wave fronts bend so that their energy is converged and concentrated against the rock, increasing hydraulic action and abrasion. In the adjoining bay, energy is dispersed and reduced, which can encourage deposition. Therefore option A is correct; the other choices involve unrelated glacial or aeolian processes.

Correct answer: B. Changes in channel width, depth, and velocity control erosion and deposition

Direct answer: B. Hydraulic geometry examines how a river channel’s width, depth, cross-sectional shape, slope, discharge, and flow velocity are related. These dimensions are not merely measurements; they influence how much energy the river has and how that energy is distributed. If discharge or slope changes, the river’s ability to erode its bed and banks, transport sediment, and deposit material also changes. A channel may become wider or deeper, develop bends, or adjust its bed and banks to the available flow. Such adjustments help produce bars, pools, riffles, meanders, levees, and floodplain features. A is wrong because karst-cave height is not the subject. C is wrong because glacier thickness is glaciology, not hydraulic geometry. D is unrelated to river channels. The important chain is: channel dimensions and flow conditions affect competence and capacity; these affect erosion, transport, and deposition; those processes build and modify landforms.

Correct answer: B. Suspended load forms fine-grained floodplains, while bed load forms bars and channel-bed features

Suspended load consists mainly of fine silt and clay kept within the flowing water, so it can travel far and settle across broad, low-energy floodplains during overbank flooding. Bed load consists of coarser particles that roll, slide, or hop along the channel floor, commonly forming bars, gravel sheets, and other bed forms. Option B correctly contrasts their depositional effects; the other choices assign river sediment to unrelated landforms.

Correct answer: B. Incised meanders, river terraces, and knickpoints

The correct answer is B. River rejuvenation occurs when a river gains renewed ability to erode downward, often after uplift or a fall in base level. Renewed incision can produce incised meanders and knickpoints; former floodplain surfaces may remain above the newer channel as river terraces. Together, these features provide strong evidence of renewed river erosion. The other options describe coastal, wind-shaped, or cave features.

Correct answer: A. Dune migration and surface abrasion by short-hopping sand grains

Aeolian saltation is the wind-driven movement of sand grains in repeated short hops. Each grain is lifted briefly, travels forward, and lands among other grains; this process transfers sediment downwind and helps dunes migrate. Impacting grains can also abrade exposed surfaces. Therefore option A is correct. A polje is a karst feature, a cirque is glacial, and a delta lobe is fluvial, so none of those depends directly on saltation.

Correct answer: A. Differential erosion of dipping hard and soft rock layers

The correct answer is A. Hogbacks and cuestas develop where alternating hard and soft rock strata dip in the same general direction. Differential erosion removes the weaker beds more rapidly, while resistant beds form ridges. A cuesta usually has a gentle dip slope and a steeper scarp slope; a hogback has steep slopes on both sides because the beds dip more sharply. The other processes do not explain these structural forms.

Correct answer: A. Former glacial meltwater and dead-ice depositional processes were active

The correct answer is A. An outwash plain is built by meltwater beyond a glacier, while an esker is a sinuous ridge deposited by a stream flowing in or beneath glacial ice. A kettle lake forms when a buried block of stagnant ice melts and leaves a depression that fills with water. Their association therefore records former glacial meltwater and stagnant or dead-ice deposition, not marine, karst, or wind action alone.

Correct answer: A. Small crescentic deposits formed by regular interaction of swash and backwash

Beach cusps are regularly spaced, rhythmic shoreline forms that commonly have alternating horns and embayments. Their development is associated with the interaction of incoming swash, returning backwash, sediment movement, beach slope, and wave conditions. This interaction can concentrate sediment into small crescentic or cusp-like patterns, so option A is correct. Glacier sliding, groundwater solution, and upper-river gorge cutting are unrelated processes.

Correct answer: C. Examining the associated landform assemblage, process, and material together

Landforms are often products of interacting agents such as rivers, glaciers, waves, wind, groundwater, and tectonic movement. A reliable interpretation therefore combines the shape, spatial association with other landforms, sediment or rock material, surface textures, elevation, and the active or possible processes. Option C follows this evidence-based assemblage approach. A single shape or memorised name can be misleading, and assuming every feature is fluvial ignores multiple-process landscapes.