Two of Mt. Rainier's glaciers, Nisqually (left) and Paradise (partially visible at right) are seen in this photo. Glaciers are slowly-moving rivers of ice that grind down the mountain. As snow builds up over time it compacts into dense ice, some glaciers are up to 300' thick. All of the park's rivers originate at the base of the glaciers, giving the water a milky look from the powdered rock.