Weathering and Erosion — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
A canyon is formed when wind blows sand into a tall pile over millions of years.
Corrected: A canyon is formed when flowing water cuts through rock over millions of years.
Canyons are carved by flowing water, not wind. Rivers slowly cut deeper into rock over millions of years, creating steep-sided valleys like the Grand Canyon.
2. Fix the sentence:
Plant roots protect rocks from weathering because they cover the surface.
Corrected: Plant roots cause physical weathering because they grow into cracks and push rock apart.
Plant roots actually break rocks apart rather than protecting them. As roots grow, they wedge into cracks and push outward with enough force to split solid rock, which is a type of physical weathering.
3. Fix the sentence:
Gravity does not play a role in erosion because only water and wind move sediment.
Corrected: Gravity plays an important role in erosion by pulling rocks, soil, and water downhill.
Gravity is a major force behind erosion because it pulls loose rocks, soil, and even water downhill. Landslides and rockfalls are examples of gravity-driven erosion.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Rocks rubbing against each other in a river is an example of abrasion.
When rocks scrape and rub against each other in moving water, the friction wears them down. This grinding process is called abrasion, a type of physical weathering.
2. A sand dune is a hill of sand built up by wind deposition.
Wind picks up loose sand and drops it in piles, forming hills called sand dunes. Dunes are a classic example of wind deposition in deserts and along coastlines.
3. When oxygen reacts with iron in rocks and turns them reddish, it is called oxidation.
Oxidation is a chemical reaction between oxygen and iron minerals in rock. It produces rust, which is why affected rocks turn a reddish-orange color over time.
4. Glaciers pick up boulders and grind the land beneath them, leaving behind scratches called striations.
As a glacier moves, rocks frozen into its bottom drag across the bedrock like sandpaper. The long, parallel scratches they leave behind are called striations.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. How can humans slow down erosion on a hillside?
Sample answer: Humans can plant trees and grass on hillsides because roots hold the soil in place. They can also build terraces to create flat steps that slow water runoff.
Planting trees and grass gives roots that grip the soil, and building terraces creates flat steps that slow rainwater so it cannot rush downhill and carry soil away.
2. Explain the difference between weathering and erosion using an example.
Sample answer: Weathering is when a rock cracks apart from ice expanding inside it. Erosion is when rain washes those broken rock pieces downhill into a stream.
Weathering breaks rock apart in place, like ice expanding in a crack. Erosion moves the broken pieces somewhere else, like rain washing them downhill into a stream. The key difference is movement.