Glaciers are giant " rivers” of slow moving ice and snow. Some glaciers are big enough to spread over entire mountains and plains! Huge glaciers, called ice caps, are so thick they can bury mountains.  Even bigger glaciers, called ice sheets, cover vast areas of continents.

     Only three percent of the Earth's water is freshwater . Glaciers are natural reservoirs for fresh water. Today, over three fourths of our freshwater comes from glaciers!

     Glaciers take a long time to form. First snow has to fall. It collects in deep valleys and hollows. Some of the snow never completely melts in some parts of the world. Then more snow falls on top of that snow. For years and years ( it can take tens of thousands of years!) the snow piles deeper and deeper. The weight packs the snow down so it is airtight, forming layers. The lower layers turn into ice and become heavier as the glacier becomes thicker. Then the lower layers begin to slide downhill.

     Glaciers come in three basic layers. The top layer is snow. The middle layer is a grainy type of mixture made up of snow and ice, called a neve. The bottom layer is a layer of ice.

     When a glacier moves it has to be very precise. When ice reaches up to about 60 to 80 feet in thickness it begins to slide downhill under its weight. This gives the ice a quality scientists call “ plastic flow”. Plastic flow allows the ice to bend and flow over the uneven surface beneath it. But the ice can't be going too fast or the ice will break and deep cracks called crevasses are created. Crevasses can also be created when the ice flows over ledges or the ice turns corners. Since the top layer of snow is not under pressure it is stiff and can't stretch over curves, so it cracks.

       Glaciers help shape the earth in different ways. Scientist have described them as “nature's bulldozers” because they don't just slip downhill. While they go down they pull, push, and pluck  rocks out from underneath them. Glaciers' ice freezes onto rough rocky surfaces. When this happens, and a glacier continues down the mountain, it plucks rocks of all shapes and sizes from the surface. This is called gouging and happens frequently.

      Glaciers are very important to people. Scientists study them to discover the new surprises they bring. They are our source of water. They help remove rocks. If we didn't have glaciers we probably wouldn't be standing here.