Surging Glaciers

By Charles Wohlforth

All Rights Reserved

Pilot Randy Kilbourn noticed something strange on the southern flank of Mount McKinley last winter. The enormous Tokositna Glacier, 20 miles long and more than 1,000 feet thick, was folding up like an accordion.

Kilbourn frequently circles North America’s highest mountain in a small plane for K-2 Aviation in Talkeetna, landing climbers and showing off the unbelievable topography to sightseers. Tokositna had always been a relatively smooth glacier, navigable by skiers and ski-planes, as it descended like a ramp through Denali National Park from around 9,000 feet elevation to about 1,000 feet.

Then something changed.

"At first it was kind of hard to figure out what was going on," Kilbourn says. Dark debris showed up on the glacier amid fresh snow. "The snow was being moved. There was fresh dirt, and you don’t see dirt in January."

Soon the glacier was looking like a rucked-up rug, with ridges and depressions hundreds of feet high, ragged edges, and immense cracks that opened and closed from day to day. Then the wrinkles began moving downhill.

"A wave is moving down the glacier, like if you stood out in a swimming pool and slapped the water."

After some 50 years of stability, the Tokositna is on the move.

Once Kilbourn and other pilots noticed the changes, a television news crew flew in and newspapers quoted glaciologists’ predictions on how far the glacier would go. It was news, but with around 100,000 glaciers in Alaska, a surging glacier is hardly unique: it’s always going on somewhere.

"It’s only those that somehow capture the media’s imagination or pose some sort of threat to some sort of structure that catch attention," says Dennis Trabant, a glaciologist with the U.S. Geological Survey.

In 1937, the Black Rapids Glacier threatened the Richardson Highway, the only link at that time between the city of Fairbanks and the outside world, when its 500-foot-high, mile-and-a-half wide face ground forward over a mossy valley as fast as 200 feet a day. When the trans-Alaska pipeline was planned in the 1970s, USGS scientists persuaded builders to reroute it away from Black Rapids to avoid having it ground up by the next surge.

"At the time we also predicted that Columbia Glacier could retreat and dump a lot of ice into Prince William Sound, and maybe they should choose a port other than Valdez for the pipeline terminal, but they didn’t listen to that one," Trabant says.

Columbia did make the predicted move, a catastrophic shrinkage that continues today. In 1989, the tanker Exxon Valdez was navigating out of shipping lanes to avoid Columbia Glacier ice when it hit Bligh Reef and caused America’s worst oil spill.

Now, Trabant says Black Rapids Glacier is ready to take off again, showing all the signs of a surging glacier getting ready to move.

Glaciers are always moving, even when they appear stable and unchanging. Snow that falls high in the mountains compresses into ice and literally flows like a river downhill. When the glacier reaches a lower elevation, warmer air or ocean water melt it as fast as it flows, and there it stops. Like a river, glaciers generally stay the same shape and size--until there’s a flood called a surge.

A small percentage of glaciers surge, their rate of advance suddenly increasing by as much as 100 times. Now, instead of ice gradually grinding over a mountainside like a huge conveyor belt, the entire glacier slips forward, sometimes eating up miles of terrain in a few months.

That’s what happened to Bering Glacier from 1993 to 1995. Located near Yakutat on the Gulf of Alaska coast, Bering is the largest glacier on the continent, measuring 30 miles wide and 145 miles long, with about the same area as the state of Rhode Island. When it surged, it pushed through lakes and lush coastal wetlands at a pace as fast as 300 feet a day. A critical migratory stop-over for rare dusky Canada geese and trumpeter swans was almost ground into oblivion--and then the glacier stopped, just in time.

The hidden mechanism that sets a glacier galloping, or shuts off its movement, is only partly understood. Scientists agree that water builds up in the slippery mud under the glacier. When the buoyancy of the ice counters its staggering weight the glacier starts to float. Lubricated and partly floating, the entire glacier then slumps downhill until an outburst flood allows the water to escape.

At Bering Glacier, the flood came just in time and the glacier stopped on a dime before it finished off the migratory bird habitat. But the water build-up probably started again soon after, as Bering seems to surge roughly every 20 years.

Glacial surges may be less severe in recent decades, as the global climate warms, but research is only beginning and the picture is far from clear. Alaska is a center for that research, because, for reasons unknown, a much larger percentage of Alaska’s glaciers surge than in other glaciated regions around the world. It’s a matter of serious interest: a glacial surge in the massive ice sheets of western Antarctica could cause a significant rise in the world’s sea level. With a better idea of why glaciers surge in Alaska, we might be able to predict if it will happen there.

Climate change research also is active in Alaska because global warming is especially pronounced here, with dramatic effects already documented on forests, tundra and sea ice. Since 1950, the state’s average temperature has risen 5 degrees Farenheit; precipitation has gone up 30 percent since the 1960s as warmer temperatures aid evaporation, increasing clouds. Glaciologists have a front row seat for the changes as they observe how ice thickness changes with the climate, although surges can mess up their careful measurements.

One famous surge taught another valuable lesson about natural changes: that people have a limited ability to fix what goes wrong.

In 1986, Hubbard Glacier, near Yakutat, surged across Russell Fjord, turning the 34-mile-long inlet into a lake. As fresh water gathered behind the ice dam, concern rose nationally for seals, porpoises and sea lions trapped away from the salt-water habitat they needed to survive. Amid world media attention, biologists and volunteers mounted a rescue mission to catch the marine mammals and move them to salt water.

The intended heroics turned into farce, however, as the animals proved impossible to catch and the media outspent the would-be rescuers, even supplying them with materials to keep the story alive. The fresh water kept rising behind the ice dam until, 80 feet above sealevel, it broke through, releasing the captive animals unharmed but leaving behind sheepish rescuers and reporters who had accomplished little other than creating their own human circus.

In Alaska, the glaciers call the shots, and mankind can only stand by and watch.