Glacier

                 Glaciers may look like big, motionless blocks of ice and snow, but they're always on the move.          
                  A glacier is a large sheet of ice that moves slowly over the land. The world's largest glaciers form where it is very cold year-round, such as the areas around the north pole and south pole. But they can form anywhere. It is cold enough for snow and ice to remain all year without melting, such as tall mountains. Glaciers can even be found in high mountain ranges near the equator, such as the northern Andes of South America.
                  Glaciers form when new snow falls faster then the old snow can melt away. As more and more snow piles up, the newly fallen snow squashes the snow beneath it. Under the weight of hundreds, sometimes thousands, of feet of snow, the lower layers of the glacier are smashed tightly together.

                  The crushing weight of all these layers of snow and ice turns the bottom-most layers of the glacier into dense ice. The ice eventually becomes so heavy that thee glacier moves downhill, like a gigantic, slow-moving river of ice.

                  Most glaciers move very slowly, just few inches a day. But some glaciers can move as much as 100 feet (30 meters) a day, about the distance from home plate to first base on a baseball field. That may not seem very fast. Even a snail can move faster than a glacier! But the movement of glaciers seems incredible when you consider that they can be the size of mountains.

                  Glaciers also grow or shrink over very long periods of time. As Earth's climate cools glaciers expand. They shrink when the climate warms.