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 and each has retreated substantially since the late 1800's. Still, forward surges in glacial flow do occur after a number of very heavy winters and cool summers, but such activity has been relatively infrequent with Olympic glaciers in recorded time. The climate influencing Olympic glaciers is wet and temperate. This is clearly shown in the Mount Olympus complex of glaciers which receive the full impact of Pacific storms.
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. As with human finance management, glaciers work with a budget and expenditure plan. 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.