Mass movements, erosion, and deposition

Direct answer: A, gravity. Mass movement is the downslope movement of soil, rock, or debris as a mass, and gravity supplies the main downward pull. Reasoning: a slope gives material a higher position; gravity attracts it toward Earth’s centre; if the material becomes unstable, it slides, falls, creeps, or flows downhill. Option A is correct. Option B, evaporation, changes liquid water into vapour and cannot normally pull rocks downslope. Option C, tidal force, acts through the gravitational effects of the Moon and Sun but is not the main cause of ordinary landslides and slope movements. Option D, magnetic force, affects magnetic materials and does not generally move soil and rock masses down slopes. Water may weaken or lubricate a slope, but gravity remains the driving force. Memory cue: mass movement means mass moving downhill under gravity.

Steep slopes make rocks and soil unstable. Exam tip: treat steep slope as a key cause of landslides.

Soil creep is very slow downslope movement of soil. Exam tip: identify it as a slow mass movement process.

Direct answer: D, wearing away and removal of rocks and soil. Erosion is the process in which soil or rock is loosened, worn away, and carried from its original place by running water, wind, glaciers, waves, or gravity. Reasoning: weathering may break material in place; erosion removes and transports it; deposition occurs when the moving material settles. Option A, settling of material, is deposition, the opposite stage of movement. Option B, freezing of water, is a physical change and may help weathering, but it is not the meaning of erosion. Option C, change in rock colour, may result from chemical alteration or weathering, but it does not necessarily remove material. Option D is correct because it includes both wearing away and removal. Exam cue: weathering breaks, erosion carries away, deposition lays down.

Deposition happens when transported material is laid down by river wind or glacier. Exam tip: link reduced energy with deposition.

A river carries material from one place to another. Exam tip: treat transportation as the link between erosion and deposition.

Debris flow is a rapid mass movement in which a mixture of loose rock fragments, soil, mud, and water moves downslope like a thick fluid. It becomes especially likely when loose material is already present on a slope and heavy or prolonged rain fills its spaces with water. Saturation adds weight, reduces friction between particles, and can reduce the stability of the slope. Gravity then helps the mixture move quickly through channels or across a hillside.

Option D is correct because water-saturated loose debris has both the material and the condition required for flow. A dry, flat road does not normally provide a saturated moving mass. Stable ground under dense forest and a low-slope plain are generally less favorable, although no landscape is completely risk-free. Heavy rainfall, rapid snowmelt, or sudden water release can trigger such movement. The key connection is loose sediment plus abundant water on a slope.

A rockfall is a rapid mass movement in which individual rocks or rock fragments detach from a steep slope and fall, bounce, or roll downward under gravity. The movement is usually sudden, and it may be triggered by weathering, earthquakes, heavy rain, freeze-thaw action, or the weakening of a slope. The important feature is the abrupt downward movement of solid rock from a height.

Option A is correct because the description directly matches rockfall. Soil formation is a slow process that produces soil, not a sudden fall. River deposition occurs when transported material settles in water, and ice melting is a change in the state of ice rather than a named type of mass movement. Rockfall is therefore a clear example of rapid mass movement, although the size of falling fragments can vary.

Slow soil movement can tilt trees and poles. Exam tip: use leaning trees as a clue for soil creep.

When river energy decreases its carrying capacity falls. Exam tip: link a slower river with deposition.

Running water can cut and carry rocks and soil. Exam tip: remember water wind ice and waves as major agents.

Sediment includes particles like sand silt and pebbles. Exam tip: understand sediment as deposition material.

A valley deepens when the river cuts downward into its bed. Exam tip: connect deep valleys with vertical erosion.

The direct answer is B: lateral erosion increases cutting sideways, toward the river banks. To understand it from the beginning, erosion means wearing away and carrying off earth or rock. The word lateral means related to the side. Therefore, lateral erosion acts mainly on the sides of a river channel rather than cutting straight upward or toward the centre of Earth. Step by step: flowing water strikes the banks; pieces of soil and rock are loosened; the current carries some material away; the banks move outward; the valley becomes wider. Option A, upward toward the sky, describes neither the usual direction nor the meaning of lateral erosion. Option B is correct because it names sideways cutting of the banks. Option C, toward the underground centre, is not the geographical meaning of lateral erosion. Option D, toward the Sun, has no connection with river erosion. A useful exam cue is: lateral means side, so lateral erosion means side cutting and valley widening.

Direct answer: C, wind erosion. When moving air picks up and carries loose sand or dust, it removes material from one place. This is erosion caused by wind, also called aeolian erosion. Step by step: dry conditions leave loose particles; wind exerts force on them; lighter particles may be lifted and heavier grains may roll or bounce; the material is transported away. Option A, marine deposition, means material settling from sea-related processes, not being carried by wind. Option B, glaciation, involves snow and moving ice. Option C is correct because the agent is wind and the action is removal and transport. Option D, a seismic wave, is a vibration produced by an earthquake and does not describe sand transport by air. Wind erosion is especially effective where vegetation is sparse and soil is dry. Memory cue: wind carrying sand away = wind erosion; wind dropping it = wind deposition.

Wind carries sand and deposits it at suitable places. Exam tip: treat dunes as a form of wind deposition.

The direct answer is A: sudden heavy rainfall can increase the risk of landslides. Rainwater enters soil and rock, raises water content and weight, and may reduce friction or cohesion between particles. If the downward force of gravity becomes greater than the resisting strength of the slope, soil and rock may move downhill. Option A is correct because it names the expected mass-movement hazard. Option B, lunar eclipse, is an astronomical event caused by Earth coming between the Sun and Moon; rainfall does not produce it. Option C, solar radiation, is energy from the Sun, not the direct slope hazard described here. Option D, polar night, is a seasonal period without direct sunlight in high latitudes and is unrelated to sudden rain on a slope. Vegetation removal and steepness can increase the danger too, but saturation is the key clue. Exam cue: sudden rain plus slope means landslide risk.

A glacier carries debris and abrades rocks. Exam tip: remember glaciers as powerful erosion agents.

Water falling from a waterfall, along with rock fragments carried by it, strikes the river bed forcefully. This intense erosional action cuts a deep hollow below the waterfall, called a plunge pool. Desert deposition involves the accumulation of material, not the erosion that forms this hollow. Exam tip: associate waterfalls and plunge pools with river erosion.

During floods a river deposits fine sediments on plains. Exam tip: treat floodplains as examples of river deposition.

The correct answer is A. As a river reaches a lake or sea, its channel usually becomes less steep and its flow spreads over a much wider area. This causes velocity and carrying capacity to decrease. A slower current cannot keep as much sand, silt, clay, and gravel moving, so the sediment settles on the bed or near the river mouth. Continued deposition may produce a delta where conditions are suitable. B is wrong because gravity continues to act and helps particles settle. C is scientifically incorrect because sediment does not instantly become gas. D is wrong because the sea does not make the river flow uphill; the river still flows downslope toward the receiving water body. Memory cue: slower water drops its load.

In debris flow water and loose material move rapidly together. Exam tip: connect it with rapid mass movement.

Roots bind soil and make slopes more stable. Exam tip: connect vegetation with landslide control.

On steep slopes the effect of gravity becomes clearer. Exam tip: link steeper slope with higher risk.

Abrasion is erosion caused by the scraping, rubbing, or impact of transported particles against a surface. In a river, pebbles and sand are moved by flowing water. As they roll, bounce, and slide along the bed, they strike and rub the channel floor and banks. Over time this action wears away the bed material and can deepen or widen the channel. The particles themselves may also become smoother and smaller.

Option A is correct because the rolling pebbles act like natural tools that grind the river bed. Light, sound, and magnetism do not normally produce this mechanical cutting in an ordinary river channel. Abrasion is related to hydraulic action, solution, and attrition, but it specifically emphasizes the wearing effect of sediment against rock. The strength of the process depends on flow energy, sediment load, and the hardness of the particles and bed.