Mass movements, erosion, and deposition

Direct answer: B, removal of loose particles by wind. Deflation is a type of wind erosion. In a dry region with little vegetation, strong or persistent winds lift and carry away loose dust, silt, and sand from the ground. When this removal continues for a long time, the land surface becomes lower and a broad depression called a deflation hollow may form. A is wrong because sea-wave deposition adds sediment and builds coastal features such as beaches or bars. C is wrong because freezing of glacial ice is an ice-related process, not wind removal of surface material. D is wrong because a river bend is a channel feature produced by flowing water. Remember: deflation means the wind “takes away” material and lowers the surface; it is erosion, not deposition.

B is correct. A drumlin is an elongated, streamlined hill associated with moving glacier ice. Its long axis is generally parallel to the direction of ice movement, so drumlin orientation can indicate the former direction of glacier flow.

A is correct. Karst regions commonly have soluble, fractured limestone. Water can enter its joints and openings, then flow underground instead of remaining at the surface. It may later emerge again at a spring, so surface streams can be scarce or disappear into the ground.

The correct answer is A. Wind moves sand grains up a dune’s gentle windward slope. After they cross the crest, they fall down the steeper slip face. Repeated transport and deposition shift sand from the upwind side to the downwind side, so the dune migrates in the direction of the wind. The other choices describe processes unrelated to ordinary dune migration.

A is correct. Mass wasting is the downslope movement of soil, rock, or debris mainly under gravity; it can occur without a river. River erosion happens when flowing water wears away the river bed or banks and carries material. Water may help trigger mass wasting, but gravity is its main driving force.

B is correct. A subglacial meltwater stream can carry sand and gravel through a channel beneath the ice. After the glacier retreats, sediment deposited in that channel may remain as a long, narrow, winding ridge called an esker. Loess, by contrast, is deposited by wind.