Alaska
The Malaspina Glacier flows out of the Saint Elias Mountains and onto a flat coastal plain that borders the Gulf of Alaska. Rocky moraines deposited by the glacier keep it from flowing into the gulf.
Glaciers may be rivers of ice, but they can take many shapes based on the underlying topography. The Malaspina Glacier in southern Alaska, for example, looks almost perfectly round from above. It is a piedmont glacier, which forms when one or more glaciers spill out onto a relatively flat plain, where they spread laterally, like pancake batter on a grill. The Malaspina is the largest piedmont glacier in the world—bigger than the state of Rhode Island.
This mass of ice covers more than 1500 square miles and is fed by several other glaciers that descend from the Saint Elias Mountains onto the coastal plain between Icy Bay and Yakutat Bay. The edge of the Malaspina comes within a few miles of the Gulf of Alaska, but its terminal moraine of piled-up rocks keeps it from reaching the water.
From the air, you can see wavy, circular, and zigzag patterns across the top of the glacier. The brown lines against the white ice are moraines—rocks, soil, and dust that get scraped up by the glacier as it moves, then are left 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 close to the center of the ice.
Glaciers that flow at steady rates tend to have relatively straight moraines, while those that periodically surge because of increased melt or steep changes in topography develop wavy moraines. These are caused by the folding, shearing, and compression of the ice. The patterns of curves, zigzags, and loops on the Malaspina Glacier are the result of such surges as well as many individual rivers of ice combining into one ice mass on the flat plain.
Measuring the thickness of a glacier isn’t a perfect science, but a useful technique involves using seismic waves to create a three-dimensional picture of the interior of the ice. Such studies have shown the Malaspina to be over 2000 feet thick. The ice is so heavy that the bottom of the glacier has sunk nearly 1000 feet below sea level. Long-term studies of the health of the glacier have revealed that the Malaspina lost more than sixty feet of thickness between 1980 and 2000. The meltwater produced from this shrinkage was sufficient to raise global sea levels by half of one percent during that time period.
The sinuous patterns in the surface of the Malaspina Glacier are especially complex because of the large number of glaciers that meet to form this huge expanse of ice.
Look for a large disc-shaped mass of ice on the gulf side of the Saint Elias Mountains, the range across southeastern Alaska and southwestern Canada. You might fly over the Malaspina Glacier en route to Juneau or Anchorage, Alaska, which lie to the southeast and northwest of the glacier, respectively.
