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Valley glacier appears poised to leave lake soon

Mendenhall lost 656 feet on its east side in 2004

Posted: Thursday, October 06, 2005

It may not take much longer for one of the world's most-visited glaciers to calve and melt out of its scenic toehold in Mendenhall Lake.

The Mendenhall Glacier could come out of the lake "in the next few years, or less," said Roman Motyka, a University of Alaska Fairbanks glaciologist based in Juneau.

The Mendenhall's hasty retreat - 656 feet lost on its east side in 2004 and 269 feet lost on its west side in 2005 - is attracting a lot of curiosity from visitors around the world, federal tourism officials said this week.

About 366,000 people visited the Mendenhall Glacier Visitor Center this year. More than ever before, "We got the question - is the glacier melting because of global warming?" said Laurie Craig, a naturalist at the visitor center, which is operated by the U.S. Forest Service.

Craig and her colleagues at the center said Tuesday that they want to begin providing visitors with scientific resources that help answer their questions about the causes - as well as the potential effects - of the Mendenhall's retreat.

"We're not qualified to say this. We want (to provide visitors) the sources," Craig said.

Their quest for information is coming at a time when Motyka's work at the Mendenhall is coming to an end. He wraps up his studies of Juneau-area glaciers this year.

His studies so far have pointed out the rapid melting of the Mendenhall and the overall warming of Juneau's climate, among other things.

Less ice is accumulating at the top of the Mendenhall and less is coming down to its base, according to mass-balance measurements by Motyka and his colleagues.

annual summertime glacier retreat

2004 to 2005

•average length of retreat across the glacier's terminus: 171 feet

•location of greatest retreat was on the west side, totalling 269 feet

2003 to 2004

•average length of retreat across the glacier's terminus: 459 feet

•location of greatest retreat was on the east side, totalling 656 feet

why did the retreat accelerate dramatically in 2004, then slow down in 2005?

Roman Motyka, University of Alaska Fairbanks glaciologist says: "basically the glacier terminus thinned to a point that was no longer sustainable in the summer of 2004, producing the big calving events. (deeper water tends to accelerate calving.) there isn't much left of the lake part of the terminus in 2005."

Motyka has also instructed the visitor center staff and Juneau residents on how Mendenhall Lake can play a vital role in controlling the glacier's massive calving periods, as it did last summer.

"This year, calving is much reduced," Motyka said. The glacier "has been pushed into a shallower area of the lake," he said. Deeper water against the glacier accelerates calving.

Though more people seem curious about the Mendenhall's retreat than ever before - no doubt because of the increased evidence and debate over climate change - there isn't much funding in place yet to continue research at the Mendenhall.

A couple of University of Alaska Southeast professors want to install a climate station and "glacier cam" at the top of the glacier, and take over Motyka's measurements of its retreat.

"There are just very few glaciers (in North America) that have this. Keeping the record going is important," said Eran Hood, a hydrologist at the University of Alaska Southeast.

Hood said he is teaming up with fellow UAS researcher Matt Heavner to seek funds for the climate station and regular measurements at the Mendenhall.

Ninety percent of Alaska's glaciers are melting and calving away, according to scientific reports.

The dramatic glacial retreat in Alaska may account for one-third of the current rise in sea levels around the world, according to a recent article published in the journal Science, Motyka said.

The good news for Mendenhall is that this summer's loss of ice was somewhat less extreme than that of the summer of 2004.

Also, the uplift of land caused by glacial retreat is causing a net gain of land in Juneau and other Southeast Alaska communities rather a loss of land due to the rising ocean, Motyka said.

On a different note: It is possible that instead of completely leaving the lake within a few years, the Mendenhall could expose a narrow, deep channel at its base that fills with water, Motyka said.

"It depends on how you define the lake," he said.

From August 2003 to August 2004, the Mendenhall Glacier lost an average of 459 feet at its base, or terminus.

That speedy retreat slowed down between August 2004 and August 2005. In that period, the glacier lost an average of 171 feet at its base.

"It's really given me a whole different sense of glacial speed and geologic time," said Craig, the naturalist at the Mendenhall Glacier Visitor Center.

• Elizabeth Bluemink can be reached at elizabeth.bluemink@juneauempire.com.



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