Erosional and depositional landforms created by various agents

The correct answer is A. Both landforms form when a stream leaves a steep, confined valley and deposits sediment as its flow slows. An alluvial cone is generally steeper and more concentrated, with coarser material near its apex; an alluvial fan spreads more widely and has a gentler slope. Neither landform forms only in the sea or in a karst cave, and cirques are glacial landforms.

The correct answer is A. In a river’s mature stage, its gradient is generally gentler, and erosion increasingly works sideways as the channel meanders. Lateral erosion widens the valley, while deposition along the channel helps a floodplain develop. A steep gradient in the youthful stage generally favours downcutting instead.

At a river mouth, deposition and erosion can operate simultaneously. The river supplies and deposits sediment, building the delta, whereas waves remove some of that material and move it along the coast by longshore transport. Therefore, the final delta form depends on the balance between sediment supply, river discharge, wave energy, and coastal currents. Option A correctly identifies both opposing processes; the other options incorrectly match geomorphic agents with landforms.

The correct answer is A. Karst commonly develops on soluble rocks such as limestone. Water enters cracks and other openings, dissolves some of the rock, and enlarges underground passages. As a result, much of the water flows below ground through features such as sinkholes and caves rather than forming a continuous surface drainage network.

Direct answer: A. Deflation is the removal of loose, fine particles such as dust and fine sand by wind. When these lighter particles are carried away from an exposed desert surface, larger pebbles and stones are left behind and become concentrated. This stony surface is called desert pavement, or reg. The pair in A therefore correctly connects the agent, the process, and the resulting landform. B is wrong because drumlins are generally glacial depositional landforms, and plucking is associated with moving glacier ice rather than ordinary groundwater. C is wrong because a cirque is a glacial erosional basin, not a landform made by sea waves. D is wrong because stalactites form mainly through mineral deposition from groundwater dripping in caves; river water is not the correct geomorphic agent in this pairing. Memory cue: wind removes fines by deflation, leaving a stony desert pavement.

Cirques are bowl-shaped hollows, arêtes are sharp ridges, horns are pointed peaks, and U-shaped valleys are all characteristic products of glacial erosion in mountainous terrain. Their occurrence together provides strong evidence that valley glaciers formerly occupied and modified the landscape. Option A is therefore the appropriate inference. Wind deposition, delta deposition, and karst processes cannot collectively explain this distinctive group of erosional landforms.

The correct answer is C. Fanhead trenching is a channel-like incision cut by a stream into the upper part of an alluvial fan. Rather than spreading out and depositing sediment across the fan, the stream becomes concentrated in a channel and erodes downward into the deposited material. The other choices describe processes unrelated to stream incision on an alluvial fan.

A is correct. Repeated sediment deposition can raise a river channel above parts of its floodplain. During a flood, water may breach the channel and switch to a shorter, steeper route. This sudden change of channel course is called avulsion.

The correct answer is C. Helicoidal flow is a corkscrew-like secondary circulation in a meandering river. It helps move sediment from the outer part of a bend toward the inner part, where slower water deposits it as a point bar. Repeated erosion of the outer bank and deposition on the inner bank cause meanders to migrate sideways over time. The other options describe glacial, karst, or wind-related processes.

Aggradation occurs when sediment supply and deposition exceed the river’s capacity to remove material, so the channel bed and floodplain gradually rise. Degradation is the opposite tendency: erosion removes bed material and lowers or incises the channel. Hence option A correctly states the geomorphic contrast. The other options confuse these fluvial processes with sea caves, aeolian deposits, or karst formations.

A composite delta develops where fluvial deposition interacts with marine processes rather than acting alone. River distributaries deposit sediment, while tides redistribute it through tidal channels and waves rework the seaward margin into beaches, bars, or spits. Different zones can therefore show different shapes at the same time. Option C is correct; the alternatives wrongly claim that one agent alone controls the entire delta.

The correct answer is A. A glacial trimline marks a boundary between terrain affected by former glacier ice and terrain that lay above or outside it. Differences in glacial marks, weathering, or vegetation can help identify this boundary and estimate the former upper ice limit. It indicates an approximate limit, not necessarily the glacier’s exact surface elevation or age.

The correct answer is B. Chatter marks are small fractures or chips made on bedrock beneath moving glacier ice. Hard rock fragments pressed against the bed can strike and scrape the rock as the glacier moves, causing local fractures and abrasion. A, C, and D describe coastal, wind, and groundwater processes rather than glacial erosion.

The correct answer is A. A cirque is a bowl-shaped hollow excavated by mountain-glacier ice. A cirque stairway is a sequence of cirques at different heights, often separated by rock steps or thresholds. It is explained by glacial erosion and overdeepening at successive levels. The other options describe processes that do not form this stepped series of glacial basins.

The correct answer is B. A glacier can leave debris unevenly, creating mounds and hollows. If blocks of dead ice are buried by that debris, their later melting can cause the overlying material to subside in places. Together, uneven deposition and subsidence help produce the hummocky surface. The other options describe processes that generally do not create this glacial terrain.

The correct answer is A. Both are glacial deposits, but they form differently. Ablation till is debris released as glacier ice melts. Lodgement till is deposited beneath moving ice, where the glacier’s pressure and movement press sediment against the bed. Thus, melting releases ablation till, while moving ice lodges sediment underneath it.

The correct answer is A. Varves are repeated lake-sediment layers that commonly reflect seasonal changes. In glacial lakes, summer meltwater may bring in coarser sediment, while finer material can settle during winter. Where the seasonal layers are distinct and preserved, a pair may represent one year, so counting varves can help establish a chronology. The pattern can vary, so annual dating requires careful interpretation.

The correct answer is A. The difference is the passage’s position relative to the water table and whether it is water-filled. A vadose passage lies above the water table, so water flows through a passage that is not completely filled. A phreatic passage lies below the water table and is filled with groundwater. These terms describe karst cave conditions, not wind, marine, or glacial landforms.

A is correct. A cave passage that was once filled with groundwater may be left above the water table when it falls. The passage can then become dry and remain as an abandoned or relict cave, recording an earlier stage of karst development.

A is correct. In warm, humid conditions, mildly acidic water can dissolve exposed limestone. Continued solution lowers and widens parts of the landscape, while less-dissolved limestone remains as steep residual towers. The other options describe glacial, coastal, or river features rather than karst solution.

C is correct. Cockpit karst is marked by closely spaced enclosed depressions, with steep or conical residual hills between them. It forms through the dissolution of limestone and is especially associated with humid tropical karst landscapes.

Correct answer: A. Water dissolves some limestone as it moves through the ground. When a drop reaches a cave, carbon dioxide can escape from it, allowing calcium carbonate to precipitate as calcite. Repeated slow dripping deposits calcite in layers, helping speleothems such as stalactites and stalagmites grow.

A is correct. In karst terrain, a surface stream can disappear into a sinkhole or ponor and continue through underground passages. The valley appears to end at the point where the stream goes underground, which is why it is called a blind valley.

The correct answer is B. Transverse dunes form where loose sand is abundant and winds blow mainly from one direction. The wind moves sand into ridges whose crests lie roughly at right angles to the prevailing wind. A limited sand supply or highly variable wind directions is less suitable for forming these ridges.

The correct answer is A. The long axis of a longitudinal, or seif, dune generally lies roughly parallel to the resultant direction of sand-moving winds. Such dunes commonly develop where winds from more than one direction influence sand movement. River depth, tides, and glacial cracks do not determine the orientation of this desert landform.