Glaciers are essentially rivers of ice but they can take many shapes depending on the underlying topography. The almost perfectly round Malaspina Glacier in southern Alaska is the largest piedmont glacier in the world – larger than the state of Rhode Island. Piedmont glaciers take shape when one or more glaciers spill out onto a relatively flat plain, where they spread laterally, like pancake batter on a grill.
The Malaspina Glacier covers more than 1,500 square miles and is fed by several glaciers, including the central Seward Glacier and the Agassiz Glacier, which descend from the Saint Elias Mountains onto the coastal plain between Icy Bay and Yakutat Bay. The edge of the piedmont glacier comes within a few miles of the Gulf of Alaska but terminal moraines – large deposits of rocks carried to the end of the glacier by moving ice – keep the Malaspina from reaching the water.
From the air, wavy, circular and zig zag patterns can be seen across the top of the glacier. The brown lines against the white ice are moraines – glacial debris including rocks, soil and dust that get scraped up by the glacier as it moves and deposited on top of the ice, usually along the sides of the glacier. When two glaciers come together, these lines of debris merge to form a medial moraine closer to the center of the ice.
Glaciers that flow at steady rates tend to have relative straight moraines, while those that periodically surge due to increased melt or steep changes in topography develop wavy moraines as a result of folding, shearing and compression of the ice. The patterns of curves, zigzags and loops on Malaspina are the result of such surges and of many glaciers combining into one mass of ice on the flat plain.
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