Glaciers form when buried snow becomes compressed and recrystallizes into a material called firn. When the formation of firn starts, the pieces are as small as sand. As the layer of firn thickens, the pieces become about the size of a corn kernal. Eventually, as the firn thickens, the weight increases. When this happens, more and more weight is pushing down on the layer, turning it into solid ice. Eventually, the ice begins to move!
