True glaciers are structurally three layered bodies of frozen water. Crevasses or deep cracks in the glaciers form as the ice is subjected to uneven flow over alpine terrain. Another structural feature is the bergschrund, which is a prominent crevasse-like opening at the head of the glacier where the ice has been pulled away from the mountain wall. There is no great advance of Olympic glaciers today, but there is not a rapid melting back of the ice either. Forward surges in glacial flow often occur after a number of very heavy winters and cool summers, but such activity has been relatively infrequent with Olympic glaciers in recorded time.
Snow nurtures the glaciers in the accumulation zone or at the origin of the ice.
Most of the melting or ablation occurs near the termini or snouts of the glaciers. A vigorous glacier will be maintained by a heavy accumulation of snow in the winter and only average melting during the summer. The freezing point in late spring and precipitation in early fall appear to be critical items in relation to this gain and loss. Excessive melt before and after the normal melt season would result in an impoverished budget for the following year. The movement of glacial ice, past and present has produced striking geological features in the Olympic Mountains.