Rocks and Minerals > Rock Cycle Activities

Physical Weathering: Stream Erosion

by Deborah Hanuscin

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Concept: Stream erosion.

As rocks are transported by streams, they are bounced around and rubbed against each other. Over a long period of time, this can cause the physical weathering, or breaking down, of the rocks into smaller particles called sediments.

Objective:

Students will be able to describe what happens to rocks that are tumbled in streams.

Materials:

• hammer
• cloth or towel
• brick or brick-size piece of relatively soft sedimentary rock, such as limestone
• clear plastic cups
• coffee can or plastic container with tight lid
• water

Procedure:

1. Wrap a brick or piece of limestone in a cloth and break into small pieces with a hammer. These should be about the size of marbles.
2. Place several pieces in a clear plastic cup and label "0." Place the rest in the coffee can.
3. Fill the coffee can with the rock pieces half full of water and close the lid tightly. Shake vigorously 200 times.
4. Remove several pieces and place them in a clear plastic cup labeled "200."
5. Place the lid on the coffee can tightly, and again shake vigorously 200 more times.
6. Remove several pieces and place them in a clear plastic cup labeled "400."
7. What would happen if the rocks were shaken 600 times? Continue the process until no more rocks are left in the container.
8. Compare the samples in the cups. How are they different? What caused this? How is what you did similar to rocks being tumbled in a stream?

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