Mass movements, erosion, and deposition

Correct answer: B. Gravity

Mass movement is driven mainly by gravity as rock and soil move downslope. In exams, distinguish it from running-water erosion.

Correct answer: C. Tilted poles and bent trees

Slow soil creep gradually shifts ground material, so poles and trees may bend or tilt. In exams, treat slow movement as the key clue.

Correct answer: A. Steep slope and water-saturated debris

On steep slopes, water-loaded debris can move downslope easily. In exams, remember slope and water together.

Correct answer: D. As a thin layer flowing uniformly

In sheet erosion, surface runoff removes a thin layer of soil over a broad area. In exams, separate it from rill or gully erosion.

Correct answer: B. When carrying capacity decreases

A river deposits sediment when its velocity and carrying capacity decrease. In exams, connect deposition with loss of energy.

Correct answer: A. Rills make small channels, gullies make larger and deeper channels

Rills are small temporary channels, while gullies are deeper and more developed erosional channels. In exams, compare size and depth.

Correct answer: C. Rock fall and debris accumulation

A talus heap forms from fallen rock fragments accumulating at the foot of a slope. In exams, identify it as foot-slope debris deposition.

Correct answer: D. Water-saturated fine debris

The direct answer is D: water-saturated fine debris. A mudflow is a rapid downslope movement in which abundant water mixes with fine loose material such as mud, silt, clay, and small sediment. The mixture behaves like a thick, flowing mass and may move through channels or across slopes after intense rain, rapid snowmelt, volcanic activity, or sudden water release. Option D is correct because both parts are essential: the debris is relatively fine and it contains enough water to flow. Option A is wrong because a flow made mainly of large boulders is better described as a rockfall or, in some cases, a debris flow, not a typical mudflow. Option B is wrong because dry sand lacks the water needed for a mudflow, although wet sediment may flow. Option C is wrong because ice crystals alone form snow or ice-related material, not mud. Mudflow is a type of mass movement, so remember: water plus fine loose sediment moving rapidly downhill.

Correct answer: A. Sediment deposition during repeated floods

During floods, rivers spread and deposit fine sediments over their banks. In exams, link floodplains with fluvial deposition.

Correct answer: C. Because water increases weight and may reduce friction

More water increases material weight and can reduce particle friction. In exams, treat water as a slope-instability factor.

Correct answer: B. Landslide can be rapid, soil creep is slow

A landslide can be sudden and rapid, while soil creep is very slow. In exams, speed is an easy identifying clue.

Correct answer: D. Velocity decreases at the mouth and sediment is deposited

A delta forms when a river loses energy at its mouth and deposits sediment. In exams, identify delta as river-mouth deposition.

Correct answer: A. Erosion removes material, deposition lays it down

Erosion removes material from a surface, while deposition lays it down elsewhere. In exams, remember removal versus accumulation.

Correct answer: B. Flow velocity is higher there

Water flows faster on the outer bend, causing stronger bank erosion. In exams, link outer bends with erosion.

Correct answer: C. Sediment deposition

On the inner bend, river velocity is lower, so sediment is deposited. In exams, connect inner bends with deposition.

Correct answer: D. It shortens slope length and slows runoff

Terracing divides a slope into smaller steps and slows runoff. In exams, treat it as a soil-conservation method.

Correct answer: A. Slope instability may increase

When root binding decreases, soil can move more easily. In exams, remember vegetation as a natural support for slope stability.

Correct answer: C. In cold regions where thawed upper soil flows

Solifluction involves slow flow of thawed, water-saturated upper soil in cold regions. In exams, link it with periglacial conditions.

Correct answer: B. Where a stream emerges from hills onto a plain

When a stream leaves hills and enters a plain, its energy drops and fan-shaped deposits form. In exams, look for sudden slope decrease.

Correct answer: D. Building check dams and planting vegetation

Check dams reduce flow energy and vegetation binds soil. In exams, connect conservation measures with runoff control.

Correct answer: A. Downslope movement of material under gravity

Gravity is the main force in mass movement, while running water is the main agent in water erosion. In exams, identify the main agent.

Correct answer: B. Larger and heavier particles settle first

As energy decreases, larger and heavier particles settle first, followed by finer particles. In exams, link deposition order with particle size.

Correct answer: C. Dry area and sparse vegetation

Loose particles are easily blown from dry, exposed surfaces. In exams, remember dryness and sparse vegetation.

Correct answer: D. It removes fertile topsoil

Removal of fertile topsoil reduces field productivity. In exams, soil erosion can also be linked with food security.

Correct answer: A. Sudden heavy rainfall

Sudden heavy rainfall can saturate debris and initiate flow. In exams, treat intense rain as a common trigger.