Linda Herchuk, age 13, of Calgary, Alberta, Canada, for her question:

Which is the world's biggest glacier?

The glaciers of the Northern Hemisphere are thought to be remnants of the last Ice Age. The Malaspina Glacier in Alaska is 1,550 feet thick and covers an area of 1,500 square miles. A series of ice fields on the slopes of the Himalayas combine to form a glacier 76 miles long. The Alps and other high mountains as far south as the equator have their glaciers. The largest one in the Northern Hemisphere is the 600,000 square mile icecap that covers most of Greenland. But all the northern ice fields account for only one sixth of the earth's total glaciers. The granddaddy of them all sits on the south pole and covers about five million square miles of Antarctica with an average thickness of 8,000 icy feet.

The Antarctic icecap could cover the United States. If the world's glaciers were bulldozed to an even thickness, they would cover the globe in ice 100 feet thick. If all this ice ever melts, the seas will rise 200 to 300 feet and all our coastal areas will be swamped. This event is unlikely. What's more, if the earth's glaciers do shrink, they would melt so slowly that we would not notice outstanding changes in our shores for many, many centuries.