Richard S. Williams Jr. 1983 <p>A glacier is a large mass of ice having its genesis on land and represents a multiyear surplus of snowfall over snowmelt. At the present time, perennial ice covers about 10 percent of the land areas of the Earth. Although glaciers are generally thought of as polar entities, they also are found in mountainous areas throughout the world, on all continents except Australia, and even at or near the Equator on high mountains in Africa and South America. </p> application/pdf 10.3133/7000019 en U.S. Geological Survey Glaciers: clues to future climate? reports