The Greenland Ice Sheet covers approximately 80% of Greenland. The weight of the ice sheet has depressed the central land to form a basin 980 feet below sea level. This ancient lake bed is sealed under more than a mile of ice in northwest Greenland. Greenland may actually be three large islands and several smaller islands, all covered by the ice sheet. If the ice sheet were to melt completely, the world’s sea level would rise by at least 23 feet.