Mount McKinley glacier makes sudden surge

Posted: Sunday, April 22, 2001

ANCHORAGE (AP) -- Glaciologists watching for a surge on the Muldrow Glacier on the north side of Mount McKinley got a big surprise last week when they learned the Tokositna Glacier on the south side of the mountain had unexpectedly taken off.

Randy Kilbourn, a pilot for K2 Aviation in Talkeetna, said he and fellow fliers first noticed changes in the glacier more than a month ago. It's now moving so fast that almost every time they see it, it looks different, he said.

By the time pilots convinced National Park Service glaciologist Guy Adema to take a look on Thursday, the changes were dramatic.

Adema said the toe of the glacier down in a valley near the Tokositna River has yet to move, but the glacier that winds back toward the base of McKinley has been rapidly folding up behind that plug like an accordion.

''The amount of deformation on it is pretty significant,'' he said.

He described undulations in the surface looking as if someone grabbed the glacier by one end and shook it like a rug.

What would normally be a relatively flat surface on the glacier now has bulges hundreds of feet high, Adema said, and depressions hundreds of feet deep. There is also significant deformation along the sides of the glacier where it has been scraping valley walls.

''The edges are just shredded,'' he said.

The Tokositna, according to Adema, has surged occasionally. ''But they were always small surges that historically start in the upper Y,'' below Mount Huntington, he said.

The latest surge starts lower down on the glacier and extends for miles. Kilbourn said that since pilots spotted the shift in February, the surge has been steadily rippling down the ice.

Adema estimated it is now within a couple miles of the glacier's terminus. He expects the toe of the glacier to start bulldozing into the Tokositna River valley in the next month or so.

Then, the changes could get really dramatic.

Adema predicts movements at the toe on the order of ''tens of meters per day. The current line of trees at the terminus would be wiped out. That will be really interesting if that happens.''

Alaska Range glaciers coming off McKinley have been active in recent years, although glaciologists remain unsure why. The Lacuna Glacier to the west of the Tokositna on the south side of McKinley regularly goes galloping, and the Yanert Glacier, also to the west on the south side, surged last year.

''Surges are generally linked to water build up in the bed of the glacier,'' Adema said. ''(But) it's really difficult to put a trigger on any of these. We have a pretty big program on the Muldrow because it surges pretty regularly.''

Glaciologists are hoping that the monitoring will enable them to spot the factors that trigger glacial surges. They doubt, Adema added, that weather changes are much of a factor, because glaciers are so thick that the effects of a single year have little impact.

Adema figures the Tokositna is at least 1,000 feet thick. It would take a massive climate change for the effects to filter their way from the surface down through such a thickness of ice.

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