Because the glacier has eroded the land surface below sea level, now that the glaciers are gone, sea water covers the valley floor. The Malaspina Glacier in Alaska is the world's largest piedmont glacier, covering over 8,000 square kilometers and measuring over 193 kilometers across at its widest point. North America's longest glacier is the Bering Glacier in Alaska, measuring 204 kilometers long. Ice Shelves Ice shelves occur when ice sheets extend over the sea, floating on the water. In thickness they range from a few hundred meters to over 1000 meters.
Ice shelves surround the entire continent of Antarctica.
The largest shelf is the Ross Ice Shelf, covering over 500,000 square kilometers. Antarctic ice is over 4,200 meters thick in some areas. The Antarctic ice sheet has been in existence for at least 40 million years. Kames small conical hills composed of sediment dropped from depressions in the glacier after it melts. Eskers long, sinuous ridges of gravel deposited as meltwater stream beds underneath the glacial ice.