Glaciers are bodies of snow that compress into large ice masses over years. They form as snowfall exceeds snowmelt on high mountains. Cracks form in the ice, which cause the glacier to move. This happens due to precipitation and temperature changes. Hurry up and visit Glacier National Park to view some of the largest glaciers in the country before they melt. The park started with 150 active glaciers; today it only has about 25.