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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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