EFFECTS OF ICE

15.17. EFFECTS OF ICE

The power of ice to alter the geosphere is amply demonstrated by the remains of past glacial activity from the Ice Age. Those large areas of the earth’s surface that were once covered with layers of glacial ice 1 or 2 kilometers in thickness show evi- dence of how the ice carved the surface, left massive piles of rock and gravel, and The power of ice to alter the geosphere is amply demonstrated by the remains of past glacial activity from the Ice Age. Those large areas of the earth’s surface that were once covered with layers of glacial ice 1 or 2 kilometers in thickness show evi- dence of how the ice carved the surface, left massive piles of rock and gravel, and

Glaciers form at sufficiently high latitudes and altitudes such that snow does not melt completely each summer. This occurs when snow becomes compacted over several to several thousand years such that the frozen water turns to crystals of true ice. Huge masses of ice with areas of several thousand square kilometers or more, and often around 1 kilometer thick, occur in polar regions and are called continental glaciers . Both Greenland and the Antarctic are covered by continental glaciers. Alpine glaciers occupy mountain valleys.

Glaciers on a slope flow as a consequence of their mass. This rate of flow is usually only a few meters per year, but may reach several kilometers per year. If a glacier flows into the sea, it may lose masses of ice as icebergs, a process called calving . Ice may also be lost by melting along the edges. The processes by which ice is lost is termed ablation.

Glacial ice affects the surface of the geosphere by both erosion and deposition. It is easy to imagine that a flowing mass of glacial ice is very efficient in scraping away the surface over which it flows, a process called abrasion. Adding to the erosive effect is the presence of rocks frozen into the glaciers which can act like tools to carve the surface of the underlying rock and soil. Whereas abrasion tends to wear rock surfaces away producing a fine rock powder, larger bits of rock can be dislodged from the surface over which the glacier flows and be carried along with the glacial ice.

When glacial ice melts, the rock that has been incorporated into it is left behind. This material is called till, or if it has been carried for some distance by water running off the melting glacier it is called outwash. Piles of rock left by melting glaciers produce unique structures called moraines.

Although the effects of glaciers described above are the most spectacular mani- festations of the action of ice on the geosphere, at a much smaller level ice can have some very substantial effects. Freezing and expansion of water in pores and small crevices in rock is a major contributor to physical weathering processes. Freeze/thaw cycles are also very destructive to some kinds of structures, such as stone buildings.