While eating breakfast one morning last summer, institute Professor of Geophysics Will Harrison watched a lake of muddy water form in a gravel depression below Variegated Glacier.
Before lunch, the lake had drained away in a river of black sediment. These indications of a surge played out against a background of fractured ice on the upper two-thirds of the small glacier in southeast Alaska.
The glacier, which extends for 10 miles from its head in the Saint Elias mountains to its foot in Russell Fjord of Yakutat Bay, moved hundreds of yards by the end of summer.
The 1995 surge of the upper part of Variegated Glacier surprised scientists by starting at least four years ahead of schedule--the surge began only 13 years after a previous one in 1982. The 1982 surge and the surge of the Variegated Glacier preceding it adhered to 17-year cycles. Scientists believe the glacier has surged at least six times since 1905, and that it will follow similar surge-and-rest patterns in the future.
Harrison will return to Variegated Glacier this summer to see if the lower part of the glacier will move, thereby completing its most recent surge before slumbering again for at least another decade. In 1982, the glacier surged in two distinct stages, taking nearly two years to move two miles.
Although relatively small, Variegated Glacier is indisputably the most studied surging glacier in the world, thanks to Harrison and University of Washington Professor Charlie Raymond. The pair initiated an exhaustive study of the ice field nearly 25 years ago.
Their work, which began in 1971 and continued for more than a decade, set the stage for an international research effort to understand the mechanisms underlying the surging glaciers of the world. During field seasons, scientists from around the globe joined them in performing a battery of tests, which included drilling boreholes to the bed of the glacier and making direct observations of its surface.
Prior to their research, little was known about what makes glaciers surge. The team eventually discovered that bad plumbing, not climate, was the primary cause.
"Surges occur when a glacier's internal plumbing system fails. The failure leads to high water pressure under the glacier, then probably to partial floatation," Harrison said. "The result is a loss of friction, and then movement downhill at a high speed."
Harrison and Raymond chose Variegated Glacier as the site for the intensive international research because it passed all the right tests.
"It is accessible in summer and winter. It's not too big, and it has a documented history of surges," Harrison said.
"Another important consideration was that we could get around the entire thing on skis," he said.