Most of the freshwater on Earth is trapped in snow and ice.
A large amount of snow that stays around all year is called a snowfield. To stick around all year, the snow must be in a place that is cool, even in summer. Often a snowfield will melt a little in the summer and grow larger in the winter when new snow falls on it. Snowfields are like young glaciers. If they grow large enough, the snow will pack together into ice and begin to flow like a glacier.
A glacier is a large amount of ice that sits on the land. The ice might look blue or white. Sometimes it looks dirty when the glacier carries a large amount of dirt and rocks. Glaciers move very slowly over time, flowing downhill because of gravity. Ice under pressure is not stiff and brittle like ice cubes from your freezer. It will flow slowly like cold honey. Most glaciers flow so slowly that you can’t see them move, not even if you watch all day. But sometimes glaciers move in great jumps of up to a meter (over three feet) a day! Some scientists study how glaciers move by watching them over many years. Other scientists study how ancient glaciers scraped the Earth’s surface long ago, changing the shape of the land.
There are two types of
glaciers. Glaciers called ice sheets cover entire continents and are found
near the poles in places like Greenland and Antarctica. But 20,000 years
ago during the last Ice Age, huge glacial ice sheets covered much of North
America, Europe, and Asia. Mountain glaciers are much smaller and sit
near chilly mountaintops all over the world.