Rocks and Minerals > Rock Cycle Activities

Physical Weathering: Plants

by Deborah Hanuscin

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Concept: Erosion of rocks caused by plants

When plants grow in soil-filled cracks of rocks, their roots may push on the sides of the crack, widening it and eventually breaking the rock apart.

Objective:

Students will be able to describe what happens to a fractured rock when a plant begins to grow in the fracture.

Materials:

• milk carton or similar disposable container
• scissors
• plaster of paris
• bean seeds

Procedure:

1. Cut the top off of a milk carton to form a container about 2½ inches high.
2. Prepare plaster of paris according to directions and fill the container.
3. Push a bean seed that has been soaked in water just under the surface of the plaster and observe for several days.
4. Describe what you observe. What would happen if the beans were in the crack in a rock? What if they were the seeds of a tree, rather than a bean plant? Can plants break apart rocks?

When plants grow in cracks in rocks, their growing roots may produce enough force to break the rock.

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