Scientists try to figure out why some glaciers move so much faster than others
The first scientists to catch a surge glacier in the act -- to film it, probe it, survey it as it lunges forward as fast as 200 feet a day -- say the key to understanding these rogues of the glacier family is their plumbing. ``We know now what causes glacier surging . . . it's water, and there's an inseparable connection between the ice flow and the plumbing,'' says Will Harrison, a physics professor here at the University of Alaska's Geophysical Institute.
As the first study ever of the surge glacier phenomenon, the 10-year undertaking to uncover how glaciers work rated a cover story in this month's Science magazine.
Along with Charles Raymond of the University of Washington and Barclay Kamb of California Institute of Technology, Dr. Harrison monitored movements of the Variegated Glacier near the point of yakutat Bay, about 200 miles north of Juneau.
Prior to a ``catastrophic surge,'' Harrison explains, water flowing out of the bottom end of the glacier slows down, indicating a blockage or disruption of the normal flow of water within and beneath the glacier. Correspondingly, when the surge of movement has ended, a pulse of mud and water is disgorged at the lower end of the glacier.
When drainage is clogged, the accumulated water lifts the glacier off its bed, ``lubricating or floating it downhill,'' he says.
As the glacier moves, the rapid motion bursts the clogs and produces violent floods of water that empty out the sides and near the bottom of the glacier.
Bore holes through the 400-meter-thick glacier helped to monitor the accumulation of water inside the glacier. The boreholes were also used to drop colored dyes into the drainage system, so that scientists could measure how long water took to run through the glacier.
Glaciers, which normally move just inches a day, move in a combination of ways.
The whole mass of ice slides along the glacier bed, and it can also flow like a river throughout the whole thickness of the ice as upper ice replaces the lower melted ice.
It is now believed that most of the movement in a surge involves the sliding over the bed.
Dr. Harrison says the a surge movement has the appearance of shearing like a deck of cards being folded.
His raw video footage of the 1983 Variegated surge is a soundless but dramatic display of a massive and sudden heave of ice growing vertically at the lower end as it lurches forward. The footage ends abruptly as the camera is toppled by the shifting ice.
The National Science Foundation (NSF)-funded study started 10 years ago, Harrison says, when he and Dr. Raymond pinpointed Variegated as the most likely of the 204 North American surge glaciers to perform in the very near future.
Since the surge phenomenon was first noticed on this 20-kilometer glacier in 1906, it has surged about every 20 years, leaving the twisted ``marbled ice cream'' trail of moraine that is characteristic of surges, he says. The last surge of Variegated was in the early '60s, and it was due for a surge in 1982 or '83.
``We picked it because of the certainty of a surge. We had to get a lot of money from the NSF and we were gambling our reputations and putting our necks on the line for this,'' he explains of the pioneering research.
Dr. Harrison adds a note about one scientific team that ``picked a glacier in the Yukon Territory and they've been there 15 years'' and the glacier hasn't done anything.
A mountaineer who didn't want to practice physics in a lab, Harrison says the team's glacier expeditions could fuel ``15 novels with all the storms survived, crevasse rescues, and helicopter wrecks.''
The excitement on the sheet of ice began the summer before the big 1982 surge when ``you could feel it and hear it'' cracking and groaning underneath the tents at night as pressure mounted within the glacier.
It is important to understand these glaciers, says Dr. Harrison, because as Alaska undergoes rapid development, glacial movement stands a bigger chance of affecting it.
As early as 1936, the Black Rapids Glacier surged and threatened the Richardson Highway. The behavior of that same glacier played a role in routing the Alaska pipeline, Dr. Harrison notes.
Further, he says glaciology is crucial to the whole system of hydrology in Alaska because glaciers feed every major river in the state.
For example, a proposed $5 billion hydroelectric system in the Susitna Basin, Harrison says, would depend on a reliable water supply.
``You may make a big underestimate if you're determining silt volume [that accumulates behind a dam] if you suddenly have a surge and get maybe 10 or 100 times more [silt than expected],'' he explains.
Although Harrison and his colleagues believe surges are not related to climate, and that surface features and even tectonic plates instead may be connected with surges, the differences between surging glaciers and ``normal'' glaciers is not understood.
Why some glaciers surge and others don't remains part of the challenge, says Dr. Harrison.