Weathering and Erosion — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Which is an example of chemical weathering?
A) Ice splitting a rock apart
B) Tree roots cracking a sidewalk
C) Acid rain dissolving limestone
D) Wind blowing sand against a cliff
Acid rain chemically reacts with calcium carbonate in limestone, dissolving it — changing the rock's chemical composition.
2. What landform is created when a river deposits sediment as it enters the ocean?
A) canyon
B) delta
C) moraine
D) sand dune
A delta is a fan-shaped deposit of sediment that forms where a river meets the ocean or another large body of water.
3. Which erosion agent carved the Grand Canyon over millions of years?
A) glaciers
B) wind
C) flowing water
D) gravity alone
The Colorado River's flowing water has carved the Grand Canyon over approximately 5–6 million years.
4. Why does freezing water crack rocks?
A) Water dissolves the minerals inside
B) Water expands when it freezes and pushes the rock apart
C) Frozen water is heavier than the rock
D) Ice makes the rock softer
Water expands about 9% in volume when it freezes to ice. This expansion exerts tremendous pressure on rock crack walls.
Part B: Fill in the Blank
Write the correct answer on each line.
1. The process in which wind wears away rock by blowing sand against it is called abrasion.
Wind abrasion acts like sandpaper, slowly smoothing and wearing away rock surfaces over long periods.
2. Chemical weathering changes a rock's chemical makeup, while physical weathering does not.
Physical weathering breaks rocks into smaller pieces; chemical weathering alters the mineral composition of the rock.
3. A glacier carves a valley into a U shape as it moves.
Glacial erosion carves broad, rounded valley floors and steep walls — a characteristic U shape.
4. Farmers plant cover crops to slow erosion of topsoil by rain.
Cover crops protect bare soil from raindrop impact and runoff, significantly reducing topsoil erosion.
5. Stalactites in caves form when dissolved limestone is deposited by dripping water.
Water carrying dissolved calcium carbonate (from limestone) drips from cave ceilings. As water evaporates, calcite is deposited, building stalactites.