Weathering and Erosion
Grade 4 · Science · Study Guide
Learn how rocks and soil are broken down and moved by natural forces.
Weathering is the process that breaks rocks and minerals into smaller pieces. It happens slowly over many years. There are two main types of weathering: physical and chemical.
Physical weathering breaks rocks into smaller pieces without changing what they are made of. Water freezing in cracks, tree roots growing into rocks, and wind blowing sand against surfaces are all examples of physical weathering.
Chemical weathering changes the minerals in rocks. Rainwater mixes with carbon dioxide in the air to form a weak acid that slowly dissolves certain rocks like limestone. Rust forming on iron-rich rocks is another example of chemical weathering.
Erosion is different from weathering. Erosion is the movement of weathered rock and soil from one place to another. Wind, water, glaciers, and gravity are the main agents of erosion. Rivers carry sediment downstream. Wind picks up sand and dust and deposits it elsewhere.
Deposition happens when eroded material is dropped in a new location. Over time, weathering, erosion, and deposition shape mountains, valleys, canyons, and beaches. The Grand Canyon is a famous example of erosion by the Colorado River cutting through rock over millions of years.
Key terms
- Weathering
- The process of breaking rocks and minerals into smaller pieces through physical or chemical means
- Erosion
- The movement of weathered rock, soil, or sediment from one place to another by wind, water, or ice
- Deposition
- The dropping of eroded material in a new location
- Physical weathering
- The breaking of rocks into smaller pieces without changing their chemical composition
- Chemical weathering
- The breaking down of rocks by changing the minerals they contain through chemical reactions
- Sediment
- Small pieces of rock, soil, and other material carried and deposited by water, wind, or ice
Flashcards
- Weathering
- Breaking rocks into smaller pieces through physical or chemical processes
- Erosion
- Movement of rock and soil from one place to another by wind, water, or ice
- Deposition
- The dropping of sediment in a new location
- Physical weathering
- Breaking rocks mechanically without changing their chemical makeup (e.g., ice wedging)
- Chemical weathering
- Breaking rocks by changing their minerals through chemical reactions (e.g., acid rain on limestone)
- Agent of erosion
- A force that moves eroded material, such as wind, water, glaciers, or gravity
- Sediment
- Tiny pieces of rock and soil transported and deposited by erosion
- Ice wedging
- A type of physical weathering where water enters rock cracks, freezes, expands, and breaks the rock
Questions
What is the difference between weathering and erosion?
- Weathering moves rocks; erosion breaks them apart
- Weathering breaks rocks apart; erosion moves the pieces
- Weathering only happens in water; erosion only happens on land
- They are exactly the same process
Show answer
Answer: Weathering breaks rocks apart; erosion moves the pieces
Weathering is the breaking apart of rocks; erosion is the movement of those broken pieces to a new location.
Physical weathering changes the chemical composition of rocks.
Show answer
Answer: False
Physical weathering only breaks rocks into smaller pieces; their chemical makeup stays the same. Chemical weathering changes the minerals.
When eroded material is dropped in a new location, the process is called ______.
Show answer
Answer: deposition
Deposition is when eroded material slows down and is dropped or deposited in a new place.
Which of the following is an example of physical weathering?
- Acid rain dissolving limestone
- Rust forming on iron-rich rocks
- Water freezing in rock cracks and expanding
- Carbon dioxide mixing with water
Show answer
Answer: Water freezing in rock cracks and expanding
Water freezing in cracks expands and breaks the rock apart physically without changing its chemistry. The other options describe chemical weathering.
The Grand Canyon was formed mainly by erosion from the Colorado River.
Show answer
Answer: True
The Colorado River has carved through rock layers over millions of years, creating the Grand Canyon through erosion.
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