Mass movements, erosion, and deposition

Waves erode cracks to form caves and then arches. Exam tip: remember erosion along lines of weakness.

The direct answer is A: a sea cave changes into an arch, and the arch finally collapses to leave a sea stack. Coastal waves first attack cracks and weak rocks at the base of a cliff. These openings become caves. Continued erosion enlarges a cave until it cuts through the headland and forms an arch. When the arch roof becomes too weak to support its own weight, it falls, while a separate vertical pillar of rock remains offshore; this pillar is the sea stack. Option A gives this exact sequence and is correct. Option B is incorrect because a delta and a floodplain are depositional river features, not the stages of a sea stack. Option C is incorrect because an alluvial fan is made by streams and a moraine is deposited by glaciers; they belong to different processes. Option D is incorrect because sand dunes and basins do not normally form a sea stack. Remember: coastal erosion often follows cave → arch → stack → stump. Do not confuse a sea stack with a depositional landform.

A beach forms by coastal deposition of material brought by waves. Exam tip: write it as a depositional landform.

Longshore drift transports sediment along the coast and forms spits. Exam tip: link it with coastal transport.

Particles embedded in ice scratch the rock surface. Exam tip: take striations as evidence of glacier movement.

A moraine is unsorted debris deposited by a glacier. Exam tip: remember it as a glacial depositional landform.

Direct answer: Option A is correct. Deflation is the removal or lifting of loose, fine surface particles by wind. In a dry region, vegetation is sparse and the soil may be loose. Strong wind can pick up clay, silt, and fine sand and carry them away, leaving behind coarser material or a lowered surface. Option A gives the exact meaning. Option B describes river flooding, which is caused by flowing water, not wind erosion. Option C describes glacial erosion, in which moving ice cuts or scrapes a valley. Option D is not the definition of a wind-erosion process; salt formation may result from evaporation and other processes. Distinguish deflation from abrasion: deflation removes loose particles, while abrasion makes wind-driven particles wear rock surfaces. Memory cue: deflation = wind takes fine material away.

Sand grains bounce near the ground so lower surfaces are abraded more. Exam tip: relate it to mushroom rocks.

The direct answer is C, fine dust-like sediment deposited by wind. Loess is a deposit made mainly of very fine silt-sized particles carried and laid down by wind. It can form thick, soft blankets over land and is often fertile when it receives enough moisture, because fine mineral particles can support plant growth. The word association is important: loess is an aeolian, or wind-made, deposit. Option A, coarse rounded pebbles, is incorrect because pebbles are much larger and are commonly moved by rivers, waves or glaciers; they do not describe the fine texture of loess. Option B, a solid lava layer, is an igneous volcanic material formed when molten rock cools, not a wind deposit. Option C is correct because it gives both the texture, fine dust-like sediment, and the agent, wind. Option D, a heap of marine fossils, is incorrect because fossils may indicate an old marine environment, whereas loess is identified by wind-blown silt. The reasoning is: wind can lift fine dry particles, transport them, and deposit them in layers; those layers are called loess. A useful memory cue is “loess = loose wind-blown dust.” Do not confuse loess with sand dunes: both are wind-related, but loess is generally much finer and more dust-like.

Wind lifts sand from the windward side and deposits it on the leeward slope. Exam tip: treat dunes as mobile landforms.

Weathering breaks material and prepares it for erosion. Exam tip: remember the difference between weathering and erosion.

Erosion removes material from its source and transportation carries it onward. Exam tip: write removal and carrying separately.

The direct answer is option C, heavy and large particles. Deposition begins when a transporting agent such as flowing water, wind, ice, or gravity loses energy or carrying capacity. Large and dense particles need more force to remain moving, so they settle first when the force becomes weaker. Smaller and lighter particles can remain suspended or travel farther. Therefore the usual order is that coarse, heavy material is deposited before fine silt and clay. Option C is correct because it states this general rule. Option A, the lightest dissolved material, is not deposited first; dissolved substances may stay in solution until evaporation or a chemical change occurs. Option B, the finest clay, is very small and can remain suspended in still or slowly moving water for a long time, so it generally settles later. Option D, only organic particles, is wrong because deposition includes mineral particles as well as organic matter, and organic particles are not always the first to settle. The exact pattern can change with density, shape, water chemistry, and current speed, but the school-level rule is large and heavy first. Memory cue: energy falls, big grains fall first.

When vegetation is removed soil becomes exposed and runoff erodes it easily. Exam tip: mention root binding.

Sheet erosion is spread out but gullies form when runoff concentrates. Exam tip: remember concentration of water.

Road or construction cuts can weaken the slope base. Exam tip: write human intervention as a landslide factor.

A dam can trap sediment in a reservoir and reduce downstream deposition. Exam tip: mention sediment supply.

The direct answer is A: particle balance against gravity fails. A pile of loose debris remains stable only up to its angle of repose, the steepest angle at which particles can stay without sliding. Step by step: gravity pulls every particle downward; friction and interlocking resist movement; as the slope becomes steeper, the downward component of gravity becomes greater; above the stable angle, resistance is insufficient, so particles move downhill. Option A is correct because it describes this loss of stability under gravity. Option B, disappearing sunlight, does not control the basic mechanical failure. Option C, closure of a river source, is unrelated to slope stability. Option D, increasing sea salt, is also unrelated. Water, vibration or earthquakes can sometimes trigger movement, but the fundamental reason here is excessive slope angle and gravity. Memory cue: angle of repose exceeded means slide begins.

Fragments from rockfall accumulate at the slope base to form talus. Exam tip: treat it as a mass movement deposit.

In solifluction saturated upper soil slowly flows over frozen subsoil. Exam tip: remember the term periglacial.

Erosion lowers high areas and deposition fills low areas. Exam tip: see it as movement toward landscape leveling.

When shear stress exceeds friction and cohesion the slope becomes unstable. Exam tip: remember the relation between driving and resisting forces.

In backwasting a slope retreats while in downcutting a river bed is lowered. Exam tip: distinguish them by direction.

Short-lived strong flow deposits heavy sediment when slope decreases. Exam tip: connect flash floods with alluvial fans in arid regions.

Loose weathered material can be removed easily by agents. Exam tip: link material supply with erosion intensity.