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UAS professors lecture on Mendenhall Glacier flooding

Presentation part of free 'Evening at Egan' series

Posted: September 22, 2012 - 11:07pm

Two University of Alaska Southeast professors discussed the emerging phenomenon of glacier outburst flooding in the Mendenhall Valley as part of UAS’ Evening at Egan Fall Lecture series in Egan Library Friday night.

Associate professor of environmental science Eran Hood and assistant professor of geophysics Jason Amundson used a PowerPoint presentation to display graphs, lists and photographs illustrating the flooding events, also known by the Icelandic term “jökulhlaup,” that took place last year and this July.

“It’s something that’s been happening in this region, but not as much locally” until recently, Hood said of the floods.

As Hood explained it, a glacier outburst flood occurs when water dammed by a glacier builds to the point where the ice dam holding it back fails. The water then rushes down the glacier — underneath it, in the case of July’s jökulhlaup — and into the lake or river below.

Last year, the larger of two outburst floods that occurred caused minor to moderate flooding in low-lying parts of the Mendenhall Valley near Mendenhall Lake and the Mendenhall River.

Water levels crested this year lower and earlier than expected, almost exactly four days after water began to release from Suicide Basin off to Mendenhall Glacier’s side, according to Amundson’s data. As such, water levels on the lake and river did not reach their flood stage.

Hood attempted to explain why the floods are occurring recently when they were previously rare.

“One of the strong trends in terms of glaciers and icefields in this region is very pronounced thinning and volume loss,” Hood said. “If you go out to Mendenhall, there’s very clear evidence of this ice thinning.”

The glacier that previously filled Suicide Basin has retreated, Hood added, leaving it a bowl with only a crust of leftover ice remaining inside it.

“The glacier ice in this basin is not being fed from the glacier anymore, so it’s essentially wasting away over time,” said Hood. “At the same time, the main glacier here, which is our dam, is thinning.”

That means Suicide Basin is able to hold an increasing amount of water, while the ice dam holding it back is becoming more buoyant and easier to force aside, Hood added.

But both professors readily admitted that there are questions that remain unanswered, despite researchers’ work to better understand the Mendenhall situation.

In order to start figuring out how much water Suicide Basin can hold and what triggers an outburst from the basin, critical facts to gauge how severe these events can be and how often they might occur going forward, Amundson said, “We have to rely on indirect observations.”

Amundson and his team installed monitoring equipment in and around Suicide Basin earlier this year, including a pressure sensor, camera and seismometer.

“At the time of the flood, we didn’t have any instruments up there that were capable of telemetry-ing data back into town,” Amundson said.

Since then, Amundson said, researchers have been able to use a radio repeater to relay data back to their Auke Bay lab.

“I feel pretty confident that the pressure sensor setup is the way to go,” Amundson added. “There’s just some bugs we need to work out.”

Hood weighed in on the monitoring equipment, which he mostly left to Amundson to explain, as well.

“What we now have is at least a rudimentary monitoring program that we’re developing, and the point of this monitoring program is to give us a better ability to … identify when the flood is starting,” said Hood.

The lecture was very well attended, with most of the lecture hall’s seats filled. All told, about 100 people were present, most of them middle-aged or elderly.

The Evening at Egan lectures are free and open to members of the public. In this week’s installment, photographer Skip Schiel will present “Israel, the Occupied Territories, and Nonviolent Resistance” on Friday.

• Contact reporter Mark D. Miller at 523-2279 or at mark.d.miller@juneauempire.com.

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