Questions: Erosion by Wind and Ice

Question 1

What is the key difference between a V-shaped valley carved by a river and a U-shaped valley carved by a glacier?

• A. V-shaped valleys are older; U-shaped valleys are younger
• B. Rivers cut narrow, deep channels producing V shapes; glaciers are much wider and erode both the bottom and sides of the valley, producing broad U shapes
• C. V-shaped valleys are in mountains; U-shaped valleys are in plains
• D. There is no real difference — all valleys are the same shape

Answer: (B)

Rivers concentrate their erosive energy in a narrow channel at the bottom of the valley, cutting downward to create a V shape. Glaciers fill the entire valley floor and sides with ice, grinding everything they touch. This produces a valley with a wide, flat floor and steep sides — the distinctive U shape. Yosemite Valley in California is a classic glacially carved U-shaped valley.

Question 2

How does wind erosion transport material differently from water erosion?

Model answer: Wind can only carry relatively small, light particles (sand, silt, and dust) and cannot move large rocks or boulders the way rivers and glaciers can. Wind lifts fine particles high into the air (suspension), bounces sand grains along the surface (saltation), and rolls the heaviest grains it can move along the ground (creep). Water and ice, being much denser than air, can transport far heavier materials.

This is why wind erosion is most effective in areas with abundant loose, fine-grained material and little vegetation — deserts and exposed agricultural fields. Wind is a good sorter: it removes fine particles and leaves coarser material behind, which is why desert surfaces often become covered with a layer of pebbles called desert pavement.

Question 3

Glaciers are the most powerful erosive force on Earth's surface.

• T. True
• F. False

Answer: True

Glaciers can move enormous amounts of material — from fine clay to house-sized boulders — and can carve valleys hundreds of meters deep. A single glacier carries and deposits more sediment than most rivers. The landscapes of Canada, northern Europe, and mountainous regions worldwide were dramatically reshaped by glaciers during the ice ages. Water is the most widespread erosive agent, but glaciers are the most powerful per unit area.