Surging Glaciers

Alaska and Yukon Territory have surging glaciers--ones that advance rapidly at regular intervals. Surging is the sliding forward of the ice at great rates; some glaciers in full surge can advance as much as 100 m (333 ft) per day.

Although surge-type glaciers are fairly common in Alaska and Yukon--there are several hundred or more--the mechanism of surges is still unknown. Surges are not caused by earthquakes, avalanches, or local increases in snow accumulation, but by some instability which occurs internal to the glacier. No particular size or shape of glacier is required to induce surges. Surging glaciers are not found in one particular climatic zone--some occur in very wet maritime environments and some in drier near-continental environments. Surging glaciers occur in the St. Elias Mountains, eastern Wrangell Mountains, and Alaska Range, but few, if any, are found in the Chugach Mountains.

In 1888, the Tlingit Indians of Yakutat described for a visiting geographer what today would be called a glacial surge that years ago overwhelmed a settlement at the head of Icy Bay in southeastern Alaska.

The Variegated Glacier, just south of the Hubbard Glacier in the St. Elias Mountains, surges at about 20-year intervals. It last surged in 1964-65, when it advanced 6000 m (over 3 miles) in one year's time. Since the early 1970s, scientific field expeditions led by the Geophysical Institute's Dr. Will Harrison have measured and monitored the motion of the Variegated Glacier to learn more about its evolution between surges and the physical changes associated with massive ice advancement. Evidence gathered from this work suggests that the most rapid movement of the Variegated Glacier occurs in summer; the increased sliding of the glacier on its bed probably has something to do with the input of melt water there. This hypothesis is a departure from two more popular ideas for the causes of glacier surging: that an internal temperature change causes the glacier to flow rapidly or that water generated by friction lubricates the glacier bed and causes the rapid flow.

Another better known surging glacier is the Black Rapids Glacier (sometimes called the Galloping Glacier) at Mile 233 Richardson Highway. In the winter of 1936-37 this glacier advanced approximately 4.8 km (3 miles) in 3 months and came within a half mile of the Richardson Highway.

Other surging glaciers in Alaska include the Muldrow, Susitna and Yanert Glaciers--all in the Alaska Range; in Yukon Territory, the Steele Glacier in the St. Elias Mountains surges.