Gordon Schaller, age 11, of Wilkes‑Barre, Pa., for his question:

HOW MANY KINDS OF GLACIERS ARE THERE?

A glacier is a large mass of ice that flows slowly over land. A glacier will form in the cold polar regions and in high mountains.There are two main kinds of glaciers: the continental glaciers and the valley glaciers.Continental glaciers are broad, extremely thick ice sheets that cover vast areas of land near the Earth's polar regions. Glaciers of this type build up at the center and slope outward, covering mountains, and plateaus.Valley glaciers are long, narrow bodies of ice that fill high mountain'valleys. Many of them move down sloping valleys from bowl‑shaped hollows located among the peaks.

Glaciers form when more snow falls during the winter than melts and evaporates in summer.