Mass movements, erosion, and deposition

Gravity pulls rock, soil and debris downslope, making it the main driving force behind mass movements such as landslides, rockfalls and soil creep. Water may increase the weight of debris or reduce friction and thus speed up movement, but gravity is the fundamental force pulling material downhill. Exam tip: when you see ‘downslope movement of material’, first think of gravity.

Mass movement means the downslope movement of soil, rock, or debris mainly under the force of gravity. A landslide occurs when a mass of earth material moves rapidly or relatively rapidly down a slope. Water saturation, removal of support, earthquakes, road cutting, and weathering can weaken a slope and help trigger the movement. The material may slide, topple, flow, or fall, depending on the type of movement.

Option B is correct because a landslide transfers soil and rock downslope as one mass or as a connected moving body. Deposition is the settling of transported material, not the name of the downslope movement itself. Condensation is the change of vapour into liquid, and transpiration is water loss from plants. Neither describes slope failure. Thus, landslide is a standard example of mass movement in geomorphology.

Soil creep is the extremely slow, gradual downslope movement of soil or loose weathered material under gravity. Rock fall is sudden and rapid, so it is not the correct term. Exam tip: If the question mentions very slow downslope movement of soil, choose soil creep.

Erosion is the process in which soil, rock, or other surface material is loosened, cut, and carried away by an agent such as running water, wind, ice, or waves. In this question, running water is the agent. It can scour the bed and banks of a stream, carry sediment downstream, and gradually enlarge or deepen a channel. Erosion therefore involves removal and transport, not merely the breaking down of material in place.

Option A, erosion, is correct. Deposition is the opposite stage in which transported sediment is laid down when the transporting agent loses energy. Condensation is the change of water vapour into liquid water, and precipitation is water falling from the atmosphere as rain, snow, or another form. Those processes do not name the cutting and removal of rock and soil by a river. The clue is the action “cuts and removes,” which points directly to erosion.

When speed decreases, river carrying capacity falls and deposition occurs. In exams, slow flow often means deposition.

Deposition is the laying down or accumulation of material that has been transported by a natural agent. Along a sea coast, waves, tides, and currents can move sand from one place to another. When their energy decreases, or when the shape of the coast causes water movement to slow, some of that sand settles on the beach. Repeated deposition can help build beaches, sand bars, spits, and other coastal landforms, although waves may also remove and redeposit the sand later.

Option A, deposition, is correct because the question describes sand accumulating at the coast. Weathering breaks rock down in place and may supply sediment, but it is not the process named for the beach accumulation itself. A volcanic eruption or earthquake may alter a coast, yet neither directly defines the ordinary settling of beach sand. The important clue is “accumulation,” which means transported sediment has been laid down after losing sufficient energy.

The sudden detachment and downward fall of rock fragments from a mountain slope is called rock fall. It commonly occurs on steep, weathered, or fractured slopes. In a landslide, a larger mass of soil, rock, and debris moves downslope, whereas rock fall mainly involves falling rocks. Exam tip: If the question mentions rocks suddenly falling, choose rock fall.

When a river enters a plain and slows down, its capacity to carry sediments decreases. Silt and sand then spread out and settle; this process is called deposition. Erosion means wearing away and removing material, whereas this question describes the accumulation of material. Exam tip: words such as “settling,” “spreading,” and “accumulation” usually indicate deposition.

The correct answer is mudflow. After heavy rainfall, soil, fine sediment, and debris become saturated with water and flow downslope as a slurry; this is called a mudflow. In a landslide, a large mass of rock or soil mainly slides or falls, whereas a mudflow moves as a water-rich flow. Exam tip: Choose mudflow when the question describes rapid downslope flow of water-saturated soil or debris.

The removal of soil and rock from the sides of a river valley by flowing water is called erosion. Therefore, cutting of the valley sides is linked with erosion. Deposition is different because it involves the laying down of sediments rather than their removal. Exam tip: Words such as ‘cutting’, ‘wearing away’, and ‘removal of material’ usually indicate erosion.

The direct answer is B: gravity is the most direct force transporting material in mass movement. Mass movement means the downslope movement of soil, rock, or debris under the pull of Earth’s gravity, often without a transporting river or wind. Step by step: a slope contains loose or weakened material; gravity pulls every mass downward; if the material becomes unstable, it slides, falls, flows, or creeps downhill; the material is deposited lower on the slope. Option A, wind speed, can transport dust and sand, but wind is not the basic direct force in mass movement. Option B is correct because gravity supplies the downward pull. Option C, sea salt, is a substance and cannot act as the main moving force. Option D, solar energy, can indirectly help weathering or evaporation, but it does not directly pull a landslide downslope. The memory cue is: mass movement equals mass moving down a slope because of gravity.

Wind may pick up and transport sand, but when the sand is laid down at a new place, the process being described is deposition. Wind deposition can form landforms such as sand dunes. Erosion mainly refers to the removal and transport of material; the key clue here is that the sand is deposited. Exam tip: Words such as “laid down,” “settled,” or “accumulated” usually indicate deposition.

Sand dunes form mainly when wind lifts, transports, and deposits sand grains where its speed decreases. This process is especially common in deserts and in some coastal areas. Running water can also deposit sand, but it usually forms riverine deposits rather than sand dunes. Exam tip: associate wind-made depositional landforms with aeolian processes.

A delta forms at the mouth of a river when the river slows down and deposits its load of silt, sand, and other sediments. These deposits commonly create a triangular landform. An alluvial fan is also depositional, but it usually forms at the foot of mountains, not at a river mouth. Exam tip: Link deposition at a river mouth with a delta.

During a flood, river water spreads beyond its banks. As its velocity decreases, fine silt is deposited over a wide area. Repeated deposition forms a flat, fertile floodplain along the river. A natural levee is also depositional, but it is a narrow raised ridge immediately beside the channel; the broader landform asked here is a floodplain. Exam tip: Flooding plus fine alluvial deposition over a wide area indicates a floodplain.

The impact of sea waves and the abrasion caused by sand and pebbles carried by them cut and remove coastal rocks. This process is erosion, so option B is correct. In weathering, rock breaks down or decomposes in place; erosion involves wearing away and removal of material. Exam tip: wave-cutting indicates erosion, while the settling of sand or other material indicates deposition.

As a glacier moves, rock fragments carried within or beneath it scrape the bedrock surface. This wearing away and removal of rock is glacial erosion, also called abrasion. Glacial deposition, in contrast, means the laying down of material rather than its wearing away. Exam tip: Wearing away indicates erosion; accumulation indicates deposition.

As a slope becomes steeper, the component of gravitational force acting downslope increases. This makes soil, rock fragments, or weathered material more likely to move downhill, so ‘Higher’ is correct. ‘Unchanged’ is incorrect because slope angle is a major factor affecting mass movement. Exam tip: Steep slopes, water saturation, and sparse vegetation can all increase mass-movement risk.

Vegetation roots bind soil particles together, reducing soil erosion and downslope movement. Leaves also reduce the direct impact of raindrops and slow surface runoff. Increasing runoff speed would cause greater erosion, not stabilization. Exam tip: For slope stability, remember that roots primarily hold and bind the soil.

Tree roots bind soil and loose rock material, helping to stabilise a slope. When trees are removed, this binding weakens; during rainfall, soil and debris can slide downhill, increasing the risk of landslides. Increased slope stability would be the opposite effect. Exam tip: Link removal of vegetation on slopes with greater erosion and landslide risk.

Direct answer: Option A, erosion removes material whereas deposition lays it down. Both processes involve earth materials such as soil, sand, silt or rock fragments, but their directions are opposite. Erosion is the wearing away and removal of material from one place by running water, wind, waves, ice or gravity. Deposition occurs when the transporting agent loses energy and drops or accumulates that material in another place. Thus option A states the essential difference in the simplest correct form. Option B is wrong because erosion and deposition do not form rainfall; rainfall is an atmospheric process. Option C is wrong because neither process is defined as increasing temperature. Option D is wrong because earthquakes are sudden movements of the crust and are not what both erosion and deposition do. A complete landform story often has three steps: weathering produces loose material, erosion transports it, and deposition settles it. Memory cue: erosion takes away; deposition puts down.

The direct answer is A: erosion helps remove materials that have been broken by weathering. These are related but different processes. Weathering breaks or decomposes rock at or near its place, while erosion removes and transports the loosened material through water, wind, ice, or gravity. The sequence is: rock is exposed; weathering cracks, dissolves, or weakens it; erosion carries the resulting particles away; deposition may later place them somewhere else. Option A is correct because it names the removal process. Option B, condensation, changes water vapour into liquid water and does not normally remove weathered rock. Option C, photosynthesis, is how green plants make food using light, carbon dioxide, and water; it is not a transport process. Option D, transpiration, is the release of water vapour from plants and does not carry broken rock away. A useful memory chain is: weathering breaks, erosion takes, deposition places.

Loose material moving downslope by gravity is mass movement. It can include both debris and soil.

Near a waterfall, the river flows with high velocity and cuts the bed and surrounding rocks, removing material. This wearing away and removal of material is called erosion. Weathering breaks rocks down in place, whereas deposition occurs when a river lays down the material it carries. Exam tip: river cutting indicates erosion; river laying down sediment indicates deposition.

The direct answer is A: a river deposits most when its current slows down. A river can carry sediment only while it has enough speed and energy. When the slope becomes gentler, the channel widens, the river enters still water, or discharge falls, velocity may decrease. The river then loses carrying capacity and drops the heaviest particles first, followed by finer sediment. Option A is correct because reduced speed causes deposition. Option B is wrong because a very fast current usually has greater erosive and transporting power, although local deposition can occur in sheltered spots. Option C is not the best answer: a suddenly dry river has no flowing water to produce the stated general process. Option D is impossible and unrelated to river action. The complete chain is: high speed carries sediment; lower speed reduces energy; sediment settles. Memory cue: slow water drops what fast water carries.