C. MOVEMENT

1. General - Ice is a brittle solid, but the weight of 50 to 60 m of ice causes glaciers to become plastic, deform, and flow. Ice masses also slip and slide along the ground. Flow top is brittle and cracks; > zone of fracture. Large cracks are called crevasses 213

2. Rates - flow fastest in center - a few mm/day to a few m/day (about the same as groundwater).

3. Budget 214 Snow accumulates above the snow line and forms ice in the Zone of Accumulation. Glaciers flow downhill and melt in the Zone of Wastage.

More snow causes terminus to advance; more snow accumulates in the winter than ice melts at the terminus in the summer.

Less snow causes terminus to retreat; less snow accumulates in the winter than ice melts at the terminus in the summer. 211

When glaciers flow into water, they calve to form icebergs.

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