Erosional and depositional landforms created by various agents

C is correct. A glacier first carves a deep, steep-sided U-shaped valley. If the valley is later flooded by seawater—often following sea-level rise or land subsidence—it becomes a long, narrow inlet called a fjord. The other options describe processes unrelated to fjord formation.

Correct answer: A. Rapids are stretches of a river where water rushes turbulently down a rough or steep channel. A waterfall has a more pronounced, usually vertical or near-vertical drop. Both are river features, but their forms of descent differ.

Correct answer: D. Glaciofluvial deposits are laid down by streams of meltwater from glaciers. Flowing water sorts and transports sediment, so sorted sand and gravel are characteristic. By contrast, material deposited directly by ice is commonly less sorted.

Correct answer: A. Meltwater flowing away from a glacier carries sediment and deposits it beyond the glacier’s margin, building an outwash plain. The running water commonly sorts the material, leaving deposits such as sand and gravel. The other options describe coastal, cave, and wind-formed features.

The governing process is differential coastal erosion. Waves attack a coast made of alternating hard and soft rocks; the softer rock is removed more quickly and retreats to form a bay, while the resistant rock projects seaward as a headland. Hence option B is correct. River levees, glacial moraines, and groundwater stalagmites are landforms formed by fluvial, glacial, and karst processes, not by this coastal contrast.

Correct answer: A. A sudden fall in base level gives a river renewed potential to erode downward. The river cuts into its bed more actively; this renewed vertical erosion is called river rejuvenation. A lower base level can also lead to features such as knickpoints or river terraces as the river adjusts.

Potholes are produced by fluvial abrasion in turbulent channels. Pebbles and coarse fragments become trapped in small hollows, then rotate under eddies and act like grinding tools; repeated circular abrasion enlarges the hollow into a rounded hole. Thus option A is correct. Wave erosion belongs to coasts, moraine deposition to glaciers, and calcite deposition to groundwater or karst environments.

The correct answer is A. Paired river terraces are matching remnants of an older floodplain on opposite sides of a valley. They form when a river renews its downcutting and cuts below that former floodplain, leaving parts of it at similar heights on both sides.

A plunge pool is the deep basin excavated at the foot of a waterfall. Falling water strikes the bed with concentrated force, while pebbles and boulders trapped in the turbulence rotate and abrade the rock, producing hydraulic scour and potholing. Longshore drift, wind-blown dust, and calcite deposition are unrelated processes, so option D is correct.

An alluvial bar forms when a river deposits part of its transported load within the channel. This happens when velocity, discharge, or carrying capacity falls, so the river can no longer move all the available sediment. Deposition may be temporary and can shift during later floods. Limestone solution and sea-cliff collapse are unrelated, while very little sediment and high uniform velocity discourage bar formation.

The correct answer is A. Tidal action commonly removes or redistributes sediment at an estuary, helping its river mouth remain broad and open. A delta forms where river-borne sediment accumulates faster than waves and tides remove it, building the land outward from the river mouth. A moraine is a glacial deposit, a delta is a surface landform, and a dune is formed by wind.

B is correct. A yazoo stream is a tributary that flows alongside a larger river for some distance. Natural levees, built from sediment deposited during floods near the main channel, can block the tributary’s direct route to the river. It therefore follows a lower path across the floodplain, parallel to the main river, until it finds a point where it can join.

A floodplain is repeatedly covered when a river overflows its banks. As floodwater spreads across the broad valley floor, its velocity decreases and suspended silt, clay, and fine sand settle out in layers. Repeated deposition renews the soil and supplies minerals, making the floodplain fertile. Glacial plucking, marine abrasion, and limestone solution are erosional or solution processes unrelated to this alluvial soil.

The correct answer is D. A glacial arête is a narrow, sharp ridge formed by erosion on opposite sides of a mountain. A lower pass or saddle-shaped gap on or between such ridges is called a col. A delta front, a wind-formed plain, and a cave roof are unrelated landforms.

The correct answer is B. A block of glacial ice can become buried in sediment. When it later melts, it leaves a depression called a kettle hole; water collecting in that hollow forms a kettle lake. Longshore drift builds coastal features, river bends are fluvial features, and dripping cave water forms mineral deposits—not kettle lakes.

Correct answer: C. A glacial arête is a narrow, sharp ridge left between two neighbouring cirques or glacial valleys. Each glacier erodes its own hollow by plucking blocks from the rock and by abrasion, in which rock fragments scrape and grind the valley sides. The headwalls of the two hollows retreat backward toward one another; this is called headward erosion. As erosion continues from both sides, the ridge becomes thinner, higher-looking, and knife-edged, so both slopes are steep. A is wrong because sea-wave deposition creates coastal deposits, not a glacial ridge. B is wrong because floodplains are broad river deposits on valley floors. D is wrong because loess is wind-blown silt and does not create a sharp glacial arête. Memory cue: two cirques attack one ridge from opposite sides.

Correct answer: D. Till is deposited directly by glacier ice, which can leave a mixture of different particle sizes with little sorting. Outwash is carried and deposited by meltwater streams; flowing water sorts particles by size and weight. Thus till is generally unsorted, while outwash is generally sorted.

Correct answer: A. A glacial erratic is a rock fragment that differs from the local bedrock. A glacier can carry it from its source and deposit it as the ice melts or retreats. Matching the rock to its source can help indicate the glacier’s former direction of movement.

A kame is an irregular mound, hill, or terrace made mainly of sand and gravel deposited by glacial meltwater. Such sediment may accumulate in contact with stagnant ice or in openings on and around a glacier; after the ice melts, the uneven mound remains. Option B is correct. Wave-cut platforms, cave pillars, and river cut banks are produced by coastal, karst, and fluvial processes.

Correct answer: A. A glacier may erode parts of a valley more deeply than others, creating an elongated hollow. After the glacier retreats, water can fill this hollow; a rock threshold or other barrier may help retain it. The resulting long, narrow lake is a ribbon lake.

Correct answer: C. A ponor is a natural opening or sinking point in a karst area through which surface water enters underground channels or passages. It connects surface drainage with underground drainage.

The correct answer is A. A ventifact is shaped when wind-blown sand grains repeatedly strike and abrade exposed rock. Over time, this wear can polish the surface or form grooves and facets. The other options describe glacial deposition, river processes, or calcite deposition in caves—not wind abrasion.

The correct answer is C. Vegetation commonly anchors the arms of a parabolic dune, while its sandy middle can move downwind. The anchored horns therefore extend upwind, toward the wind’s source. This contrasts with typical barchan horns, which point downwind. A dune’s orientation is not determined simply by whether a sea or river is nearby.

The correct answer is B. Star dunes form where winds blow from several directions over time. The changing wind directions move sand toward a central mound and build arms that extend in different directions, giving the dune its star-like shape. A single weak wind direction, glacial processes, or tides do not explain this form.

C is correct. Wind commonly transports coarse grains close to their source because they settle sooner when the wind loses energy. Finer particles, such as silt and dust, can remain suspended for longer and travel much farther. The actual distance also depends on wind strength and particle properties.