Glaciers and avalanches are both made of frozen material. They can both occur in cold, mountainous areas. There are some major differences between glaciers and avalanches, however. Glaciers are large masses of ice and snow that move very slowly, while avalanches occur suddenly when a large mass of snow falls off a mountainside and tumbles to the ground. Glaciers can last for thousands of years, whereas avalanches occur and are over in a very short period of time.