Weathering and Erosion — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Tree roots growing into rock cracks cause physical weathering.
Root wedging physically pries rock apart as roots grow and expand. The rock's chemical composition doesn't change.
2. When carbon dioxide mixes with rainwater it forms a weak acid that dissolves limestone.
CO₂ + H₂O → carbonic acid (H₂CO₃), which dissolves calcium carbonate in limestone and marble.
3. A V-shaped valley is carved by a fast-flowing river.
Rivers cut downward, creating narrow, steep-sided V-shaped valleys. Glaciers carve U-shaped valleys.
4. Wind erosion is strongest in flat, dry areas like deserts.
Deserts have sparse vegetation and loose, dry soil, making them highly vulnerable to wind erosion.
5. Gravity pulls loose rocks downhill in an event called a landslide.
Landslides (rockslides) occur when gravity moves large masses of rock and soil rapidly down a slope.
6. A moraine is a ridge of sediment left behind by a glacier.
Moraines are deposits of rock debris carried and left by glaciers as they advance or retreat.
7. Ocean waves erode cliffs along the coastline.
Wave action erodes sea cliffs and coastal rock through hydraulic action, abrasion, and chemical weathering.
8. Sediment that settles at the bottom of a lake is an example of deposition.
When water in a lake is still, suspended particles settle by gravity — a classic example of deposition.
9. The repeated freezing and thawing of water in rock cracks is called frost wedging.
Frost wedging (freeze-thaw action) is one of the most powerful mechanical weathering processes in cold climates.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
physical weathering
→ rock broken by ice or roots
sediment dropped in a new place
chemical weathering
→ minerals changed by acid rain
rock broken by ice or roots
erosion
→ sediment carried away by wind or water
minerals changed by acid rain
deposition
→ sediment dropped in a new place
sediment carried away by wind or water
Physical weathering → broken by ice/roots; chemical weathering → minerals changed by acid; erosion → sediment carried away; deposition → sediment dropped.