Erosional and depositional landforms created by various agents

The correct answer is A. Deflation is the removal of loose fine material by wind. As wind carries away finer particles, coarser pebbles may remain and form a protective surface layer called desert pavement. This layer shields finer sediment below and is itself difficult for ordinary winds to move, so less material is available for deflation.

The correct answer is A. A yardang is a ridge carved mainly by wind in a dry environment. Persistent winds erode exposed and weaker material more rapidly than resistant or sheltered parts. This uneven erosion produces the yardang’s streamlined, asymmetric form.

The correct answer is A. When waves approach the shore obliquely, swash carries beach sediment up the beach at an angle. Backwash then flows downslope toward the sea, usually more directly. Repeated movement creates a zigzag path, while the net transport of sediment is along the coastline; this is longshore drift.

A is correct. Waves erode the base of a coastal cliff, helping it retreat and leaving a platform. The platform’s width can be affected by how resistant the rock is, the energy of the waves, and how long sea level remains relatively stable. More resistant rock may erode more slowly.

The governing concept is coastal deposition and barrier formation. A bay-mouth bar is a ridge of sand or shingle deposited across, or partly across, the entrance of a bay by wave-driven sediment transport. It can reduce the exchange of seawater, leaving a shallow lagoon behind the bar; continued infilling may produce marshy conditions. Rivers do not instantly become glaciers, and poljes and drumlins are unrelated landforms, so option B is correct.

The governing concept is high-energy coastal deposition. During storms, waves are larger and more powerful, so they can carry and deposit coarse shingle farther inland and at a higher level than the material placed by ordinary wave action. A storm beach therefore commonly records an unusually energetic event. Karst water, glacial downcutting, and river flooding do not define this marine deposit, making option C correct.

The governing concept is the balance between marine erosion, sediment transport, and deposition. Resistant rocky coasts commonly show wave-cut cliffs, notches, caves, and platforms because wave erosion is dominant. Sandy coasts contain mobile sediment, so swash, backwash, longshore drift, and wind can rearrange it into beaches, bars, spits, or dunes; deposition may therefore be prominent. The absolute words in the distractors are incorrect, so option A is correct.

B is correct. When a stream leaves a steep mountain valley and spreads onto flatter ground, it loses speed and transporting power. Coarser sediment tends to be deposited near the fan’s apex, while finer material can be carried farther outward. Local patterns may vary, but particle size generally decreases away from the source.

A is correct. An inselberg and a monadnock are isolated residual uplands that stand above the surrounding lower terrain. They remain prominent because their rock has resisted weathering and erosion more effectively than much of the surrounding material. Their precise usage can vary by regional and textbook terminology.

A is correct. The epiphreatic zone is periodically flooded as groundwater levels rise and fall. During a flood, a passage may become water-filled and carry faster-flowing water and sediment; at other times it may contain air. These changing conditions can erode, enlarge, or modify parts of the cave passage.

The correct answer is C, marine wave erosion. Waves attack weaknesses in a rocky coast, enlarging caves and arches and eventually leaving isolated stacks. Continued undercutting causes cliffs to retreat, while the former shore platform remains as a wave-cut platform. Headlands persist where rock is relatively resistant and bays develop where rock is weaker. Groundwater, glacial deposition, and wind deposition cannot produce this complete coastal assemblage.

Wave refraction occurs when waves enter shallow water at different angles and their speed changes. Around a bay, the wave fronts tend to spread, so wave energy becomes less concentrated and weaker. The lower energy reduces the ability to keep sand and shingle in motion, allowing deposition on the bay’s shore. By contrast, energy is often concentrated on projecting headlands, increasing erosion there. Therefore, option C is correct.

The governing concept is differential glacial erosion within a cirque. Ice can abrade and pluck the sheltered cirque floor more intensely, producing overdeepening, while the threshold or outlet is eroded less. The relatively resistant, higher outlet zone is left as a rock lip or threshold. Hence option D is correct; waves, river levees, and wind deflation do not explain this glacial form.

A is correct. A glacial trough is a broad valley shaped by moving ice, commonly with a U-shaped cross-section. Where the trough ends abruptly at a lower valley or plain, that termination is called a trough end. The other options describe features of deltas, caves, and dunes, not glacial valleys.

The governing concept is glacial deposition at the confluence of valley glaciers. When two glaciers merge, the lateral moraine on the right side of one and that on the left side of the other come together along the junction. Their rock debris is carried down the centre of the combined ice as a dark stripe called a medial moraine. Therefore option B is correct; the other choices describe unrelated coastal, aeolian, or karst features.

The governing concept is deposition against or within stagnant glacier ice. Meltwater places sand and gravel along ice margins, in crevasses, or in tunnels. When the supporting ice later melts, the sediment loses support, collapses, and may be faulted or deformed. This produces uneven, irregular ice-contact deposits, so option C is correct. Wave erosion, parallel river flow, and karst evaporation do not provide the necessary ice-collapse mechanism.

The governing concept is the different fluvial sources of fan deposits. An outwash fan develops where sediment-laden meltwater leaves a glacier and loses competence, depositing sorted sand and gravel. An alluvial fan forms where ordinary mountain streams emerge from a steep valley onto a flatter piedmont and deposit their load. Thus option C correctly distinguishes the agents; tides, karst water, and wind are not the defining agents.

A is correct. Permeable, jointed limestone allows water to enter cracks and flow underground, reducing surface runoff. Water containing dissolved carbon dioxide can gradually dissolve limestone along these routes, helping form underground drainage and karst features such as caves and sinkholes.

The correct answer is B. A polje is a broad, closed depression in a karst landscape. Water usually drains through ponors or other underground openings. If these outlets are blocked, or rainfall exceeds their capacity, water can collect temporarily on the polje floor and form a seasonal lake.

A doline is a closed depression commonly formed when soluble rock, especially limestone, is dissolved by groundwater or when the roof of a cavity collapses. A high concentration of dolines therefore signals active karstification under suitable groundwater and drainage conditions. Option C is correct; river deposition, marine erosion and glacial plucking do not directly produce abundant dolines.

The correct answer is D. A karst window is a surface opening that reveals part of an underground stream or cave system. It can form when a cave roof collapses, exposing the water below. The other choices describe glacial, coastal, or dune features rather than karst drainage.

The correct answer is B. A rimstone dam is a raised calcite rim, often found around shallow pools in caves. As carbonate-rich water flows, conditions such as carbon dioxide loss can cause calcite to precipitate along an edge. The growing rim can hold back water and form small pools or terraces.

B is correct. Desert varnish is a thin, commonly dark coating on exposed rock, especially in arid regions. It often contains concentrated iron and manganese oxides, along with fine material such as clay. The other options describe marine, glacial, or karst features, not a rock-surface coating.

Correct answer: C. Aeolian means produced by wind. Sand grains carried over a dune crest commonly fall or slide down its steep slip face, building inclined layers called cross-bedding. The dip of these layers can indicate the direction in which the sand was transported. Cave calcite, glacier melting and a ponor are unrelated to this wind-depositional structure.

Correct answer: A. A blowout forms when wind removes sand from a surface. Vegetation at its margins binds the sand with roots and reduces erosion, helping to stabilize the arms of a developing parabolic dune. The less-protected central part can continue to move downwind. The other choices describe processes unrelated to dune formation.