Experiment Frost Wedging
Download the printable Experiment Sheet here.
Frost wedging is a process by which rocks are broken apart due to the repeated freezing and thawing of water within its pores or fractures.
Frost wedging, also called "freeze thaw cycling", is an important way that sediment is physically created from hard rocks, such as igneous or metamorphic rocks exposed in large mountain ranges. As water infiltrates the pores or fractures of a rock during the day, it freezes at night. Freezing water results in a volume increase of 9% versus liquid water. In a confined space, tremendous pressure is exerted on the rock by the ice causing the rock to break open.
Over time this process repeats and breaks rock down into smaller sediments. Chemical dissolution and other forms of weathering assist in creating the final clays, silts and sands we see transported downstream by erosion.
In this experiment we will demonstrate how freezing water can physically weather solid material by breaking it apart.
Plaster of Paris
- Mix Plaster of Paris with water in a seperate cup.
- Add a small water balloon to a second cup, fixing to the bottom by tape or a pin from underneath. Fill this cup with the plaster of paris mixture, making sure the balloon is completely covered and is not touching the sides of the cup.
- Let the plaster of paris fully harden around the water balloon.
- Place the fully hardened plaster + cup in the freezer overnight.
- Cut or tear the cup away from the frozen plaster and observe the effects on the plaster from the now frozen water balloon.
Questions to consider:
- Had you observed cracks/fractures in the plaster before placing the plaster in the freezer? Did you notice any fractures or cracks after removing it from the freezer?
- What happens to water when it freezes? Does it expand or contract?
- If we let the plaster and balloon ice melt, would the plaster fall apart? If we did this 100 times, what would happen to the plaster?