Sherry Bowen, age 11, of Columbia, S.C., for the question:
How does a glacier move?
The study of glaciers calls for mittens and earmuffs It is cold work, but even more interesting than building a snow man. For glaciers follow their own fascinating rules of behavior. In same respects a glacier flows like a stream, only far more slowly. After all, it is made of ice and ice is no more than water frozen solid. A stretch of ice must be a certain size before it may call itself a glacier. It need be only a mile or so wide, but it must be 200 to 300 feet thick. This thickness is necessary for it to behave and move like a glacier. There are several kinds of glaciers, each with its own shape.
The valley glacier is a tongue of ice licking down a mountain slope into a valley. There are more than 1,000 of these valley glaciers, big ones and small ones, in the Swiss Alps.
The piedmont glacier is shaped like a frying pan with a lid on it. The handle is a valley glacier sloping up a mountain. The pan is a mass of ice spread out over a flat area. It may have more than one handle to it for these handles are the valley glaciers which feed the massive fields of ice below.
The ice sheet glacier is an irregularly shaped massy sprawled over hill and dale. When it is only a few miles wide it is called an ice cap. The ice sheet of Greenland is one to two miles thick and big enough to cover the Carolinas eight times over. The giant ice sheet which covers Antarctica is large enough to cover the United States and all her territories.
All these glaciers, big and small, are on the move. The valley glacier is most like a slowly flowing stream. It is sliding down hill. The surface moves from a few inches to a few feet each day, the sides moving faster than the center.
A large, sprawling ice field moves out from the center. The piedmonts and the ice sheets are all spreading slowly out towards their edges. The surface of a glacier is a mass of cracking, creaking ice. Cracks and crevices yawn down to about 150 feet. The ice below this level is under terrific pressure from the ice on top of it. It is crushed into an even mass and it flows even more like a river. The deep ice of a glacier moves somewhat faster than the surface ice.
A glacier ends when it reaches air above freezing point. The valley glaciers end near the snow line. Above this line the air is always cold enough to keep the ice from melting. The ice at the foot of the valley glacier melts and runs down in rushing streams and waterfalls.
The edges of the Antarctic sheet meet the sea. Here the pounding waves tear at the giant cliffs of ice. Great chunks are torn loose and float away as icebergs. Icebergs also break from the ice sheet of Greenland.
A glacier is constantly being renewed by fresh snow. The white blankets fall one upon another, pressing down with their weight. The snow beneath becomes pressed into ice. And ice is really a fragile rock. It breaks bends and moves under its own weighty Actually, it is the glacier’s own weight which causes it to move as it does.