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USGS CMG InfoBank: Movement of Glaciers

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Comment: 04:29 - 05:25 (00:56)
Source: Annenberg/CPB Resources - Earth Revealed 23. Glaciers
Keywords: "Louis Agassi", stress, ice, gravity, "geologic time", "plastic deformation", glacier, "glacial flow", friction, river, stream

Our transcription: Subject to extreme instantaneous stress ice shatters like glass, but if stress such as gravity is applied gradually over a long period of time, the ice bends.
This process called "plastic deformation" explains how glaciers move.
Generally, ice must accumulate to a thickness approximately 20 meters before movement starts.
Pulled by gravity, ice in a glacier typically shifts down slope a few millimeters per day.
To study glacial flow, Louis Agassi and his students built a hut on the ice itself.
They observed that the center of the glacier moved most quickly while friction slowed down movement along its sides.
A similar phenomenon is observed in rivers and streams.

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