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These activities help demonstrate the changing nature of glaciers. Glaciers, without much stress have great plasticity and will flow as we expect a glacier to flow. Add high stress such as a sudden jolt or pull and the mass experiences brittle failure, which is what happens when a crevasse opens up or an iceberg breaks off. As you vary the surface and incline, you can observe the way a glacier behaves in nature. If the temperature of the ice changes the flow of the ice will change, too.
Glaciers move in the same direction as gravity dictates.
They move forward or retreat backward depending on what
is happening in the environment. As long as a glacier
accumulates more snow than it loses, it will move forward.
When it loses more than it gains, it will begin retreating.
If a glacier is retreating, it is losing ice mass.
Different forces may cause a glacier to move. Glaciers like the interior ice sheet in Antarctica move in part because of internal deformation. Gravity pulls down on the ice causing great pressure. As the ice sheet sits on land, the pull tends to spread it out from the center. This spread happens because of changes to the ice crystals as the pressure causes the changes in the crystals.
The West Antarctic Ice Sheet provides a good example
of basal sliding. This occurs when water is under the
base of the ice. This water might be there due to melting,
rain water, meltwater that has worked its way through
the glacier, or other melting. The melting point of
ice under the pressure of a glacier is actually lower
than the normal 32° F. As the ice thickens and mass
increases, the melting point lowers. The layer of water
under the ice reduces friction and invites the ice to
slide faster downhill. Basal sliding causes a glacier
to move ten times faster than a glacier moving due to
internal deformation. The land surface under the glacier
determines the speed also. When a glacier is on wet,
soft earth, it moves much like when it is on a layer
Environmental factors can indeed impact glaciers. However, it is important to remember that not all glaciers are the same. The glaciers in Antarctica are polar glaciers. The glaciers in North America are temperate glaciers. They are so named by their locations, obviously. More importantly they are influenced by the local climate. A temperate glacier is much warmer than a polar glacier. They are still frozen, but respond faster to environmental changes. A long-term change of a few degrees in the Antarctic where the average temperature is well below freezing won’t be as significant as a few degrees change in our latitudes. It takes time for something as massive as the Antarctic ice sheets in that freezing environment to change.
Teacher Notes on the lessons and material preparation:
Activity: Glacier Goo
Activity 1: How does a glacier travel down a mountain?
Activity 2: How does temperature affect the speed of a glacier?
Activity 3: What are the characteristics of Glacier Goo at different temperatures?
http://www.asf.alaska.edu:2222/anatomy/anatomy_begin.html (good graphic to use in teaching the parts of a glacier)
http://www.pbs.org/edens/patagonia/tglacier.htm (a lesson on making a glacier)