Erosional and depositional landforms created by various agents

Correct answer: A. A cone has a steeper slope and coarser material, while a fan is more spread out and gentler

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.

Correct answer: A. In the mature stage, when the gradient decreases and a floodplain develops

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.

Correct answer: A. The river deposits silt, while waves erode and redistribute that same sediment

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.

Correct answer: A. Water quickly enters the ground through cracks and solution-enlarged passages

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.

Correct answer: A. Wind deflation — desert pavement

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.

Correct answer: A. Former glacial erosion was effective in the area

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.

Correct answer: C. A stream cutting downward into the fan surface

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.

Correct answer: A. When a river flows in a channel raised by its own deposits and floodwater can escape into a shorter, steeper route.

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.

Correct answer: C. Lateral migration of meanders and development of point bars

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.

Correct answer: A. In aggradation the channel bed rises, while in degradation the channel bed is incised downward

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.

Correct answer: C. Because rivers, tides, and waves affect different parts

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.

Correct answer: A. The former ice-surface or ice-limit level

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.

Correct answer: B. Abrasion and small fractures caused by hard particles beneath a glacier

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.

Correct answer: A. Glacial erosion and overdeepening at several elevation levels

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.

Correct answer: B. Irregular deposition of glacial debris and melting of buried ice blocks

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.

Correct answer: A. Ablation till is released as glacier ice melts, whereas lodgement till is pressed onto the bed beneath moving ice.

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.

Correct answer: A. They record seasonal deposition and can sometimes provide an annual chronology.

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.

Correct answer: A. Vadose passages form above the water table, where water flows through an air-filled passage; phreatic passages form below the water table, where the passage is water-filled.

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.

Correct answer: A. It may become a dry, higher passage abandoned by groundwater.

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.

Correct answer: A. Strong limestone dissolution in a warm, humid climate, leaving steep residual towers.

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.

Correct answer: C. Closely spaced closed depressions with conical residual hills between them.

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. It allows carbon dioxide to escape and calcite to be deposited.

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.

Correct answer: A. A surface stream ends at a sinkhole or ponor and flows underground.

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.

Correct answer: B. An abundant supply of sand and wind from one dominant direction.

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.

Correct answer: A. Roughly parallel to the resultant wind direction.

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.