Erosional and depositional landforms created by various agents

A flood plain develops beside a river where repeated floods spread beyond the channel and deposit layers of fine alluvium. Lower gradients and broad valley floors encourage lateral movement, overbank flow, and deposition of silt and mud. The surface is gradually built and renewed by successive floods. Steep upper-course erosion, coastal wave action, and accumulation above the snowline are controlled by different processes and do not form river flood plains.

An alluvial fan forms where a steep mountain stream emerges onto a flatter piedmont surface. The sudden reduction in gradient and flow confinement lowers water velocity and transporting capacity. Coarse gravel, sand, and other sediments are deposited outward in diverging channels, producing a fan-shaped body. The process is fluvial deposition caused by declining stream energy, not tides, glacial plucking, or wind-made lakes.

Delta formation requires a positive sediment balance at the river mouth. The river must deliver substantial alluvium, while waves, tides, and currents must be weak enough that they do not remove it faster than it arrives. The sediment then accumulates and builds distributary channels and delta lobes. Strong marine removal prevents delta growth; upper-valley erosion or wind speed alone is not the decisive condition.

The correct answer is B. Braided rivers divide into several shallow channels around bars of deposited sediment. When the river carries more sediment than a single stable channel can transport, sand and gravel accumulate and split the flow. Changes in discharge can also shift and reshape these bars. Very little sediment and stable flow are more likely to support a single channel.

An arête is a narrow, sharp-edged ridge produced when glaciers erode the mountain from two sides. Typically, adjacent cirques or glacial valleys retreat toward one another, leaving only a steep knife-edge divide between them. Option A is therefore correct. River-mouth deposition, wind-built dunes, and retreating waves do not create this high, serrated glacial ridge.

A glacial horn is a sharp, pyramidal peak left when three or more cirques erode a mountain summit from different sides. Continued headward erosion removes the intervening ridges and leaves a steep central pinnacle. Thus option B is correct. A single river, coastal sand deposition, or groundwater planation cannot produce this characteristic multi-sided glacial peak.

The correct answer is D. A drumlin is an elongated hill shaped beneath moving glacial ice. Its long axis usually lies parallel to the direction of ice flow, so its alignment indicates the general direction in which the glacier moved. The drumlin’s shape can sometimes help show the sense of movement as well.

The correct answer is B. An outwash plain forms beyond a glacier when meltwater streams deposit sediment. Flowing water sorts the material by size, so an outwash plain is generally made of sorted sediment. A moraine, by contrast, is deposited directly by glacial ice and is usually unsorted, with particles of different sizes mixed together.

A sea cave develops where waves exploit joints, faults, or other weak zones in a coastal cliff. Continued hydraulic action and abrasion enlarge the opening; if erosion progresses through the headland from opposite sides, the openings join to form a sea arch. Option C correctly combines wave erosion with structural weakness. River floods, subglacial flow, and wind deposition do not create this sequence.

The correct answer is A. Waves erode the base of a sea cliff, forming a notch. As the notch grows, the cliff face may collapse and retreat inland. The rocky surface left at its former base is a wave-cut platform. The other options describe glacial deposition, a river landform, and a groundwater-related feature.

A tombolo is a depositional coastal landform in which a bar, usually made of sand or shingle, connects an island with the mainland or another island. Wave refraction and converging longshore transport can reduce energy in the sheltered zone and encourage deposition. A spit need not connect an island, while the other options describe river, wind, or glacial features; therefore C is correct.

A seif, or linear dune, is a long narrow ridge of sand aligned broadly with the effective wind direction. It commonly develops where winds are strong and persistent, or where two similar wind directions help extend a ridge rather than forming a crescent-shaped dune. Floodwater, cirque erosion, and cave dripping create unrelated landforms, so the long linear wind deposition described in A is correct.

Loess is a widespread, usually blanket-like deposit of wind-blown silt and very fine dust. The particles may be carried over long distances and deposited when wind speed decreases; the resulting material can form deep, fertile soils, although it may be vulnerable to erosion when exposed. Unsorted glacial debris is till, a sea-arch remnant is a stack, and a river-edddy hollow is a pothole, so B is correct.

Yardangs are streamlined ridges carved in arid regions by persistent wind erosion. Wind-blown sand abrades exposed rock, while deflation removes loose particles; weaker layers are worn down faster than resistant layers, leaving elongated ridges aligned with the prevailing wind. Longshore drift, glacial deposition, and meander-neck cutting are unrelated coastal, glacial, and fluvial processes. Therefore C is correct.

The correct answer is D. Wind carries sand close to the ground, where the particles abrade the lower part of an exposed rock more strongly. This undercuts the base, while the upper part is less worn and remains broader, giving the rock its mushroom-like shape.

The correct answer is C. An inselberg is an isolated hill of resistant rock that remains standing above the surrounding, more extensively eroded landscape. The contrast results from differential erosion: less resistant rocks wear away faster than the harder rock mass.

The correct answer is B. In a meander cut-off, the river breaks through the narrow neck of a bend and takes a shorter route instead of flowing around the whole loop. The active channel therefore becomes shorter and relatively straighter. The abandoned bend may later become an oxbow lake.

The correct answer is A. Repeated waves erode the foot of a sea cliff and can cut a wave-notch into its base. The overhanging rock loses support and may collapse under gravity, leaving the cliff face farther inland. Repeated erosion and collapse cause the cliff to retreat.

The correct answer is A. A wind gap is a dry valley, pass, or notch that may preserve the route of an earlier stream. If the stream is diverted, for example by river capture, the former channel can remain as a dry gap. The other options describe different landforms or settings.

The correct answer is A: sediment generally becomes finer downstream. Coarse particles tend to settle when the river loses energy, while smaller particles can remain in transport farther downstream. This is a general pattern, and local conditions can create exceptions. B reverses the usual pattern; C ignores the way flowing water sorts sediment; and large boulders are not found only at river mouths.

The correct answer is B. An estuary is a river mouth where fresh water mixes with seawater. Tides, waves, and coastal currents can carry away or stir up sediment, helping the mouth remain broad. In contrast, a delta forms where river sediment accumulates and builds land at the mouth. A is wrong because an estuary is not formed only by glaciers; C is wrong because estuaries are not restricted to deserts; and D is wrong because a river is essential to an estuary.

The correct answer is A. Lateral erosion acts on the sides of a river channel, wearing away its banks and widening the valley. Erosion on the outer banks of bends also helps meanders develop and enlarge. Cirques and arêtes are mainly glacial landforms, stalactites form in caves through mineral deposition, and barchans are wind-made dunes.

Landform identification is most reliable when morphology, material and geomorphic process are considered together. Shape may suggest an agent, but rock type, sediment texture and evidence of erosion or deposition help confirm whether rivers, glaciers, wind, waves or groundwater produced it. Therefore option C is best. Colour, a local name or elevation alone can be misleading and cannot establish origin.

An ox-bow lake forms when a meander loop becomes isolated from the main channel. During a flood, water may cut through the narrow meander neck and adopt the shorter route. Deposition then seals the abandoned ends, leaving the former loop as a crescent-shaped lake. Thus option B is correct; deep-valley erosion, glacial till and sea waves are not the normal mechanism.

A drumlin is an elongated depositional landform shaped beneath moving glacier ice. Its streamlined long axis is generally parallel to the direction in which the ice flowed, so a group of drumlins can reveal former regional ice movement. Option C is therefore correct. Shoreline height, old river meanders and seasonal desert winds are unrelated to the orientation of this glacial feature.