Mass movements, erosion, and deposition

Correct answer: B. Contour ploughing means ploughing along lines of equal height, called contours, rather than up and down the slope. The furrows made across the slope act like small barriers. When rain falls, these barriers interrupt the direct downward path of water, reduce its speed, encourage some infiltration, and lessen the amount of soil carried away. A is incorrect because ploughing straight downhill would create channels that allow water to gain speed and remove more soil. C is incorrect because contour ploughing does not remove all roots; plant cover and roots generally help hold soil. D is unrelated because sea waves are produced in marine environments, not by field-ploughing methods. The basic chain is: contour furrows across the slope → slower runoff → less soil erosion. Memory cue: “Contour follows the level, not the slope.”

Correct answer: A. Terracing divides a long, steep slope into a series of shorter, level or gently sloping steps. Each step interrupts the uninterrupted downhill path of rainwater. As a result, the effective slope length is reduced, runoff loses speed, more water can infiltrate, and less soil is detached and transported. Vegetation or crops on the terrace may further help hold the soil, but the central idea in this question is control of slope length and runoff velocity. B is incorrect because terraces are agricultural landforms and do not separate a river from the sea. C is incorrect because terracing cannot remove gravity; it only reduces the opportunity for gravity-driven water flow to accelerate over a long slope. D is scientifically unrelated and impossible in this context. Memory cue: “Terraces turn one long slope into many short steps.”

Direct answer: A, downward. In the upper course, a river usually flows down a steep gradient. Gravity gives the water high energy, so it cuts mainly into the river bed. This is called vertical, downward, or deepening erosion. The process commonly produces narrow V-shaped valleys, gorges, rapids, and waterfalls, although the exact result also depends on rock type, joints, and variations in slope. A is correct because the dominant action is cutting downward into the bed. B is wrong because a river does not normally erode only upward; upward change may occur through uplift or weathering, but it is not the main river-erosion direction. C is wrong because flowing water is active and moving, not still. D is not a meaningful direction of erosion and does not describe the upper-course process. Farther downstream, the slope usually becomes gentler and lateral erosion and deposition become more important. Memory cue: upper course cuts deep; middle course cuts sideways more strongly; lower course deposits more sediment.

The correct answer is A. A river terrace is a step-like remnant of an older floodplain above the present river. It can form when the river cuts downward, leaving part of the former floodplain standing at a higher level.

The correct answer is D. A knick point is a sharp break in the slope of a river’s long profile. During rejuvenation, a fall in base level or uplift can renew a river’s ability to cut downward, producing a steep step in its profile; this may appear as a rapid or waterfall.

Correct answer: C. Slightly acidic rainwater dissolves exposed limestone, especially along its joints and cracks. Over time, the cracks widen into grooves called grikes, while the blocks of limestone between them are called clints. The other options describe unrelated glacial, coastal, or river processes.

A is correct. In the youthful, upper course, a river commonly flows down a steep gradient, so it has substantial energy to cut into its bed. This vertical erosion can help form deep, narrow valleys and gorges. The pattern is a general model: actual erosion also depends on factors such as rock type and flow conditions.

B is correct. In the conventional river-stage model, lateral erosion becomes more important as the river enters its mature stage and develops wider channels and meanders. Faster flow along a bend’s outer bank tends to erode it, while slower flow along the inner bank favours deposition. Together these processes can shift the channel sideways.

The correct answer is C. In abrasion, sediment carried by water, wind, waves, or ice scrapes and wears away a rock surface. In attrition, transported particles collide with one another, gradually becoming smaller and often rounder. Both are processes of erosion, but abrasion wears down the surface being struck while attrition wears down the particles themselves.

The correct answer is D. Hydraulic action is erosion caused by moving water acting directly on rock. Water forced into cracks exerts pressure; air trapped in the cracks may also be compressed. Repeated river flow or waves can widen the cracks and loosen pieces of rock. The other options describe deposition, wind transport, or glacial processes rather than hydraulic action.

The correct answer is A. Solution erosion occurs when water dissolves minerals in rock and carries the dissolved material away. It is especially important in soluble rocks such as limestone. Option B describes attrition, and option C describes saltation; neither is solution erosion.

The correct answer is B. Rills are small, shallow channels cut into soil by surface runoff. If runoff continues and removes more soil, these channels can widen and deepen into gullies. Thus, gullies are larger and more developed than rills.

The correct answer is A: river capture. Headward erosion extends a stream valley back toward its source. If one stream erodes headward far enough to breach the divide, it can divert the headwaters of a neighbouring stream into its own channel. This transfer of drainage is called river capture, or stream piracy. The other choices are coastal, wind-formed or cave features.

The correct answer is B. A knickpoint is a sharp break or step in a river’s longitudinal profile, marking an abrupt change in channel gradient. It can result, for example, from a change in base level, uplift, or differences in rock resistance; a waterfall or rapid may occur there.

The correct answer is A. A river’s capacity is the total quantity of sediment it can transport under given flow conditions. Its competence is the largest individual particle it can move. For example, a river may carry a large total amount of fine sediment yet be unable to move a large boulder. Capacity concerns the total load; competence concerns the maximum particle size.

A is correct. Solifluction is the slow downslope movement of water-saturated soil, commonly in cold or periglacial environments. During thaw, the surface layer can become wet while frozen ground below restricts drainage. The soil then moves gradually under gravity, sometimes forming lobes.

Correct answer: B. Wind abrasion occurs when moving particles strike and wear rock. Sand grains commonly travel by saltation: they make short hops and return to the surface, so many impacts occur close to the ground. This can wear down the lower part of exposed rocks more strongly, sometimes forming pedestal or mushroom-shaped rocks. Cave water and tides do not explain this wind process.