A glacier is a large body of ice and snow.. It forms because the snow in an area does not all melt. Each year, more snow is added. The weight of all the snow creates pressure and this pressure turns the lower parts of the snow into ice.
After this happens for many years, the glacier will start growing large. It becomes so heavy that gravity causes the ice to move. It flows downwards like water but very slowly. A glacier only moves about 50 metres per year. New snowfalls replace the parts that flow away.
Glaciers will only form in places that are cold enough and get enough snow over time. It takes hundreds of years for a glacier to form. There are two kinds of glaciers:
- Continental glaciers are glaciers that spread out over a large area of land. They were created mostly during the Ice Age. There are continental glaciers in Greenland and Antarctica. They often flow downwards into the sea and break up. The broken parts that float in the sea are called icebergs.
- Alpine glaciers form in mountanous areas. They are smaller than continental glaciers. Alpine glaciers usually flow until they reach a point where the temperature is warm enough that the ice melts completely during the summer.