GLACIERS
Although glaciers account for much less erosion than running water, in
themselves, they are much better eroders than streams. Geological
features that are characteristic of glaciation are significantly different than
those of running water.
A glacier is a thick ice mass that originates on land from the accumulation
of, compaction and recrystallization of snow. Glaciers flow, generally
downhill, and accumulate, carry and deposit sediment. The characteristics
of the sediment carried and deposited by glaciers are very different from
those of streams.
There are two fundamental types of glaciers
Valley or alpine glaciers are the ones we normally think about. Each is a
stream of ice bounded by precipitous rock walls that flows down-valley from
an accumulation center near its head.
Ice sheets are much larger and flow out in all directions from one or more
centers and completely obscure all but the highest areas of underlying
terrain. For instance, Greenland is covered by an ice sheet that covers 1.7
million square kilometers (80% of the island) with an average thickness of
1500 meters. The Antarctic ice sheet is 13.9 million square kilometers (1.5
times the area of the US) and attains a maximum thickness of 4300 m.
Continental ice sheets cover about 10% of the earth's land area. When an
ice sheet flows into a bay and no longer sits on land but floats, you get an
ice shelf.
An interesting point to note is that Antarctica's ice sheet constitutes 80% of
the world's ice and 2/3 of the fresh water. If this ice melted, the sea level
would rise 60-70 meters, covering most of the densely populated parts of
the globe.
