Erosional and depositional landforms created by various agents

The governing concept is coastal depositional sediment transport. Waves and currents can accumulate sand or gravel in the sheltered water between an island and the mainland. When the deposit forms a connecting bar, it is called a tombolo. A delta develops where a river enters standing water, a cirque is a glacial hollow, and a pothole is a rounded cavity drilled by swirling river sediment. Therefore option A is correct.

The correct answer is B, a sinkhole. This feature belongs to karst topography, which develops where soluble rock such as limestone is acted on by water. Rainwater absorbs carbon dioxide from the air and soil and becomes mildly acidic. As it moves through cracks, it dissolves some limestone. Continued solution may enlarge underground cavities or weaken the surface until the ground forms a rounded or funnel-shaped depression called a sinkhole. A, a delta, is built by river deposition. C, a sand dune, is deposited by wind. D, a sea cliff, is a steep coastal rock face commonly shaped by wave erosion. Thus only B fits both the limestone and solution clues. Memory cue: soluble limestone plus a surface depression equals sinkhole.

The slow chemical removal of limestone by groundwater is called solution, or chemical dissolution. Rainwater absorbs carbon dioxide from the atmosphere and soil, forming weak carbonic acid; this water passes through cracks and dissolves calcium carbonate in the limestone. Deflation is wind removal of loose material, abrasion is mechanical scraping, and deposition is accumulation, so D is correct.

Rivers, wind, glaciers and waves are geomorphic agents because they shape the Earth’s surface through erosion, transportation and deposition. Rivers cut valleys and deposit alluvium, glaciers carve and deposit glacial material, wind forms dunes and loess, and waves produce coastal cliffs and beaches. They are not climate zones, soil types or vegetation categories, so A is correct.

Gorges and waterfalls are mainly produced by river erosion. A gorge is a deep, narrow valley cut by a river, often where vertical erosion is strong, while a waterfall develops where differences in rock resistance or a sudden change in river gradient causes water to plunge. Wind commonly forms dunes, groundwater forms caves, and waves shape coasts, so B is correct.

Moraines and drumlins are glacial depositional landforms. A moraine is an accumulation of till deposited along, beneath or at the end of a glacier. A drumlin is a streamlined hill of glacial sediment shaped beneath moving ice. Rivers form alluvial features, wind forms dunes and loess, and waves form coastal deposits, so the glacier in option C is correct.

Barchans and loess are both formed by wind deposition. A barchan is a crescent-shaped sand dune produced where wind moves and deposits sand, usually in dry regions with limited vegetation. Loess is a blanket-like deposit of fine wind-blown silt that may accumulate far from its source. Rivers, glaciers and groundwater create different landforms, so D is correct.

A sea cave, sea arch and sea stack represent successive stages of coastal wave erosion. Waves first exploit joints or weak zones in a coastal cliff to create a cave. Continued erosion enlarges the cave into an arch; when the arch roof collapses, an isolated stack remains. River, glacial and wind deposition do not produce this sequence, so A is correct.

A delta, a beach and a sand dune are all depositional landforms, although different agents create them. A river deposits sediment at its mouth to form a delta; waves deposit sand and pebbles along a coast to form a beach; and wind deposits sand to build a dune. Thus the common process is deposition, making option B correct.

In the upper course, the river usually flows down a steep gradient, giving vertical erosion strong power. The channel cuts downward into its bed faster than it widens sideways, producing a narrow valley with sloping sides and a V-shaped cross-section. Deposition, coastal currents, and lime deposition do not explain this youthful fluvial landform.

B is correct. A barchan is a crescent-shaped dune formed by wind that mainly blows from one direction. Its horns point downwind, in the direction the wind is moving; the broad, convex side faces the incoming wind.

D is correct. In dry regions, wind-blown sand abrades exposed rock most effectively near the ground, where sand grains are concentrated. The lower part is worn away faster than the upper part, leaving a narrow base and a broader top.

A is correct. Waves enlarge cracks in a coastal headland into caves. Continued erosion can cut through the headland to form an arch. When the arch roof collapses, an isolated column of rock remains as a sea stack. The sequence is cave, arch, stack.

The governing concept is coastal sediment balance. Constructive waves usually have a relatively strong swash and weaker backwash, so more sand and shingle are carried up the beach than returned to the sea. This net gain builds or widens the beach, making B correct. Very high erosive wave energy generally removes beach material, while glacier abrasion and groundwater solution are not direct beach-deposition mechanisms.

D is correct. Groundwater dissolves some limestone as it moves through cracks and carries dissolved minerals into the cave. When the water drips into the cave, calcium carbonate is deposited in layers. Deposits hanging from the roof form stalactites, while deposits building upward from the floor form stalagmites.

A is correct. In caves, mineral-rich drops can deposit calcium carbonate. A stalactite builds downward from the roof, while a stalagmite builds upward from the floor where drops land. They are cave deposits, not river, sea, wind, glacier, or delta landforms.

B is correct. Groundwater can dissolve soluble rock such as limestone and form caves. The collapse of a cave roof, or subsidence above underground cavities, can produce a sinkhole. The other pairs are associated mainly with river or coastal deposition, wind action, or glacial processes.

The governing concept is the relationship between river velocity and carrying capacity. A fast river can transport larger and more sediment particles, but when its velocity falls on a plain, its energy decreases. The river then becomes unable to carry part of its load and deposits sediment on the bed or banks. Thus option B is correct. Glacial plucking, wind abrasion, and wave erosion are processes controlled by different agents, not by a slowing river.

The governing concept is wind transport and deposition. Wind can carry sand and dust while its speed and energy remain sufficient. When wind speed decreases because of rough ground, obstacles, increased surface friction, or a change in airflow, its carrying capacity falls. The sediment is then released and deposited, forming features such as dunes or sheets of dust. Therefore option A is correct; the other choices describe rain, glacier, or marine conditions.

A moraine is a glacial depositional landform made of unsorted material such as rock fragments, sand, gravel, and clay. A moving glacier transports this debris and deposits it at its sides, beneath the ice, or at its terminal end when the ice melts or retreats. Thus option D is correct. Groundwater, waves, and wind can create other deposits, but they do not produce moraines.

A, wind, is correct. Deflation is the removal of loose particles by wind. As wind removes exposed dust or sand, the ground may be lowered into a shallow depression called a deflation hollow.

Direct answer: Option B is correct. A sand dune is a mound or ridge of loose sand formed mainly by wind deposition. First, wind transports sand grains by short jumps called saltation, by rolling or creeping along the ground, and sometimes by suspension. When wind speed decreases, or when vegetation, a rock, or another obstacle reduces the wind’s energy, the grains settle. Continued deposition builds a dune. Option A is wrong because marine erosion removes coastal material rather than building ordinary inland dunes. Option B is correct because it names both the agent and the process. Option C is wrong because glacial abrasion scratches and wears rock beneath moving ice. Option D is wrong because river downcutting makes channels and valleys, not wind-shaped sand mounds. Memory cue: erosion removes, deposition builds; dunes are built when wind drops its sand.

A sea cliff forms through coastal erosion, especially hydraulic action and abrasion by waves. Repeated wave attack cuts a notch at the base of a coastal rock face; the unsupported upper material collapses, and continued retreat leaves a steep cliff. Option A is correct. Wind deposition, delta building, and groundwater deposition are depositional processes and do not explain this steep coastal landform.

Option B is correct. Waves attack weak points in coastal rocks, such as joints and cracks. Repeated wave impact and the abrasion of rock by sand and pebbles enlarge these openings, which can develop into sea caves. No particular year applies to this geomorphic process.

Direct answer: Option C is correct. A sea arch is a coastal erosional landform formed in a headland or cliff. Waves first exploit cracks and weak zones to create caves. If erosion continues from opposite sides of a narrow headland, the two caves enlarge until they meet or cut through the rock. The stronger rock above the opening remains as an arch. Option A is wrong because delta distributaries are channels formed where a river deposits sediment at its mouth. Option B is wrong because a sand dune is a wind-depositional landform. Option C correctly gives the usual development from caves enlarged through a headland. Option D is wrong because a glacial cirque is a bowl-shaped hollow eroded by ice. The usual coastal sequence is cave, arch, stack, and stump, although local conditions can vary. Memory cue: “cave cuts through the headland to become an arch.”