Students will learn that as water freezes, it changes form, expands and produces force. Students will also identify moving ice as the primary component of a glacier.
Grade: 4 – 6
Time: two 1/2 hour sessions
Subjects: Chemistry, physics, earth science
Teacher Background:
The description of the work of glaciers in mentioned how meltwater in a glacier seeps into cracks in rocks and then expands and breaks up the rocks. Erosion of rock by ice expansion is most dramatic near a glacier headwall, but the process takes place anywhere that ice accumulates in the winter and thaws in the summer.
Materials:
- Access to a freezer
- A tray
- A glass bottle or jar with a tight cap
Procedure:
1. Read out loud as a classs Then have the class do a short experiment.
2. Fill a jar with water to the point where there is no room for air in the jar, then close the jar tightly.
3. Place the filled jar on a tray and have someone place it in a deep freeze.
4. The next time the class meets to work with glaciers, have someone bring the tray with the jar carefully back to the classroom. The jar lid should be bulged out and the glass should be cracked.
5. Show the tray to the class and set it aside to let the ice melt.
6. Go on to Activity 2; look at the jar on the tray at the end of class or at the end of the day. The ice will be melted and the glass will have collapsed in a heap. This is what happens when glacial meltwater seeps into headwall rocks and freezes. When the bergschrund gap moves slightly away from the headwall and melting occurs, the surface rocks of the headwall collapse onto the glacier.
Variations and Extensions:
Experiment with containers of different thicknesses and of different materials.
Assessment:
Have students write their own stories about how rocks can “float” on water.
