Belle Jarnieuski, age 7, of Winnipeg, Canada, for her question:

Is it really true that glaciers move?

Everybody knows, of course, that a glacier is made of ice, cold solid ice. But the real thing does not look at all like a giant ice cube. It does not look much like everyday ice. The fact is, the glacier ice is mixed with tons of dirt, gravel, muddy boulders and gritty sand. The ice, almost always, is dirty gray. And a glacier may be as big as a mountain with straight cliffs higher than the highest building.

Ice, you know, is really one of the earth's rocky minerals. In the sun, it melts and turns to runny water. But while ice is frozen solid, it is a rocky mineral. Surely a great glacier of rocky mineral cannot move by itself. But it can and it does. It moves because ice is a fragile mineral, easily cracked and broken. As a glacier grows thicker, it gets heavier    heavy enough to crack under its own weight. The heavy ice of a thick glacier shoves the lower layers out of shape. The whole glacier is always moving slowly changing its shape. The edges of a flat glacier push out from the center. A glacier perched on a mountain is always sliding slowly down the slope.