Glacial Advance and Retreat
A glacier is
basically an iceberg on land, that moves by gravity and the pressure of
increasing snow from the top pushing on the bottom, causing it to flow
down-hill; no different than squeezing silly putty between you hands, or pouring batter out onto a
pan. There are two kinds of glaciers; alpine glaciers in mountains formed of
blue-green ice, and ice sheets like those in Antarctica and Greenland. If ice builds up faster than it melts, a glacier
will slowly crawl down to the valley floor, or "advance" until it reached a
climate of warmer temperature. If ice and snow accumulated as fast as it
melted, the glacier would be "stationary". However, if the ice was to
melt, without amassing any new weight, the glacier would be said to
"retreat". Glaciers are very powerful; they can pick up huge boulders and drop
them in the middle of a not-yet-created prairie, or plow
straight through valleys and scratch cliff faces with the ice chunks protruding
from the bottom. Those scratches are called striations. Below are two images of glaciers at Lake Louise, by the BC-Alberta border.
