Erosion and Weathering
Learn
Have you ever noticed how rocks and cliffs can look worn and smooth? Or how rivers cut through the land? This happens because of two important processes: weathering and erosion.
What is Weathering?
Weathering is when rocks and soil are broken down into smaller pieces. This happens slowly over time. Wind, water, ice, and even plants can break rocks apart!
What is Erosion?
Erosion is when broken pieces of rock and soil are moved from one place to another. Water, wind, ice, and gravity can all carry these pieces away.
How Do Weathering and Erosion Work Together?
First, weathering breaks rocks into smaller pieces. Then, erosion carries those pieces away to a new place. Together, they change the shape of the land over many, many years.
Types of Weathering
- Water weathering: When water gets into cracks in rocks and freezes, it expands and breaks the rock.
- Wind weathering: Wind blows sand and dust against rocks, wearing them down slowly.
- Plant weathering: Tree roots can grow into cracks in rocks and push them apart.
- Animal weathering: Animals that dig, like gophers, can break up soil and rock.
Types of Erosion
- Water erosion: Rivers and rain carry soil and rocks downstream.
- Wind erosion: Wind picks up dust and sand and moves it to new places.
- Ice erosion: Glaciers (huge ice sheets) push rocks and soil as they move.
- Gravity erosion: Rocks and soil can fall down hills and mountains.
Examples
Let's look at some real examples of weathering and erosion.
Example 1: The Grand Canyon
What happened: The Colorado River has been flowing through rock for millions of years.
How it works: Water erosion slowly carved away the rock, creating a canyon that is over a mile deep!
Result: One of the most amazing landforms on Earth was created by water.
Example 2: Beach Rocks
What you see: Smooth, round pebbles on the beach.
How it works: Ocean waves tumble rocks around, wearing off their sharp edges.
Result: Rocks that were once rough and jagged become smooth over time.
Example 3: Cracks in the Sidewalk
What you see: Plants growing through cracks in concrete.
How it works: Plant roots push into small cracks and make them bigger.
Result: Eventually, the sidewalk breaks apart. This is weathering!
Example 4: Muddy Water After Rain
What you see: Brown, muddy water flowing in streams and gutters.
How it works: Rainwater picks up loose soil and carries it away.
Result: Soil moves from one place to another. This is erosion!
Example 5: Desert Rocks
What you see: Unusual shaped rocks in the desert.
How it works: Wind blows sand against rocks, slowly wearing them into strange shapes.
Result: Wind weathering creates natural sculptures over thousands of years.
Practice
Answer these questions about weathering and erosion.
1. A tree root grows into a crack in a boulder. Over time, the boulder splits in two. Is this weathering or erosion?
Show Answer
Weathering. The rock was broken into smaller pieces but not moved to a new location.
2. A river carries sand downstream. Is this weathering or erosion?
Show Answer
Erosion. The sand is being moved from one place to another by water.
3. Wind blows dust from a field to a nearby road. Is this weathering or erosion?
Show Answer
Erosion. The dust (tiny pieces of soil) is being moved by wind.
4. Water freezes in a crack in a rock, and the rock splits. What type of weathering is this?
Show Answer
Water weathering (or ice weathering). When water freezes, it expands and breaks the rock.
5. A rockslide sends boulders tumbling down a mountain. Is this weathering or erosion?
Show Answer
Erosion. The rocks are moving from one place to another because of gravity.
6. Name one thing that can cause weathering.
Show Answer
Possible answers: water, wind, ice, plants, or animals.
7. Name one thing that can cause erosion.
Show Answer
Possible answers: water (rivers, rain), wind, ice (glaciers), or gravity.
8. Which happens first: weathering or erosion?
Show Answer
Weathering happens first. Rocks must break apart before the pieces can be moved away.
9. A farmer notices that after heavy rain, the soil on a hill has moved to the bottom. What caused this?
Show Answer
Water erosion. The rain carried the loose soil down the hill.
10. Why are rocks at the bottom of a waterfall often smooth and round?
Show Answer
Water weathering wears away the sharp edges of rocks over time. The moving water tumbles the rocks and makes them smooth.
Check Your Understanding
Question 1: What is the main difference between weathering and erosion?
Show Answer
Weathering breaks rocks apart into smaller pieces. Erosion moves those pieces to a new location.
Question 2: Give an example of how plants can cause weathering.
Show Answer
Tree roots can grow into cracks in rocks. As the roots get bigger, they push the rock apart and break it.
Question 3: How did water create the Grand Canyon?
Show Answer
The Colorado River slowly wore away rock through erosion over millions of years, cutting deeper and deeper into the earth.
Question 4: Why might a farmer plant trees or grass on a hillside?
Show Answer
Plant roots hold soil in place and help prevent erosion. Without plants, rain could wash the soil away.
Next Steps
- Go outside: Look for signs of weathering and erosion in your neighborhood. Can you find worn rocks or places where soil has moved?
- Do an experiment: Put a piece of chalk in a jar of water. Shake it gently every day for a week. Watch how the chalk wears down!
- Keep learning: In the next lesson, you will learn about Landforms and how weathering and erosion help create mountains, valleys, and plains.