Rocks and Minerals > Rock Cycle Activities

Physical Weathering: Ice

by Deborah Hanuscin

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Concept: Erosion of rocks caused by freezing and thawing of ice

As water located in a fracture of a rock freezes it expands. Repeated cycles of freezing and thawing may widen the fracture to the point of breaking the rock into smaller pieces.

Objective:

Students will be able to describe what happens to fractured rocks when water in the fractures freezes and thaws.

Materials:

• milk carton, paper cup, or similar disposable container
• freezer
• plaster of paris
• water
• scissors
• butter knife

Procedure:

1. Cut off the top of a milk carton or other container so that it forms a cup-like shape about three inches tall.
2. Prepare plaster of paris (follow directions on package) and pour into container.
3. Use the butter knife to cut a narrow one-inch-deep groove into the plaster before it dries. The groove should not touch the edges of the container. Allow to dry completely.
4. Carefully tear the container away to reveal your block. Measure the size of the groove (width and length). Fill the groove with water and place the block in the freezer.
5. After the water has frozen, remove the block and record your observations. Allow the ice to melt, then place in the freezer again. How many times do you have to repeat this process before the block breaks? Where might this process occur in nature?

When water freezes, it increases its volume. As freezing water expands and becomes ice, it exerts a force. This force may be sufficient to widen cracks in rocks and eventually break them apart. This is another type of physical weathering.

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