Glaciers are heavy ice forms that are found at the North and South Poles or on high mountain tops. They are formed when layers of snow fall in an area that has temperatures way above freezing all year long. Snow layers fall one year, never melt, and new snow falls on top of the old snow until it is stacked up very high. After many years the older snow is flattened by the weight of the snow on top and becomes ice. Eventually the snow piles up high enough to form a glacier. When the glacier forms over an area that has a slope, gravity pulls it down the slope. Glaciers grow to be many miles long, and in some places glaciers are almost a mile high. Glaciers hold more than one-half of the fresh water on earth today.