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One of the great ‘spectacles of nature’ is moving through Denali

Published: Apr. 12, 2021 at 7:36 PM AKDT
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ANCHORAGE, Alaska (KTUU) - Muldrow Glacier on the side of Denali is on the move, and it’s moving fast.

The glacier began surging most likely in December 2020, according to scientists with the National Park Service. A surge is when a glacier’s movement speeds up 10 to 100 times faster than normal. Only about 1% of glaciers surge but the ones that do, surge on a regular basis.

“Surge-type glaciers generally do it with some periodicity, but they’re not well understood and it’s not totally regular periods,” said Guy Adema, resource manager and physical scientist with the National Park Service.

Muldrow Glacier surges about every 50 years. Its last surge was around 1956 or ’57, so it’s a little late.

“We’ve been looking forward to the chance of Muldrow surging since about 2000,” Adema said. “It’s been thickening in its upper regions through measurements we’ve made since about 2000 and it’s been very much stagnant in the lower reaches.”

Glaciers are formed on slopes. The weight of the ice and the pull of gravity means they move slowly downhill, carving out valleys. Though they look like solid pieces of ice, glaciers are constantly changing— melting and moving — but they change slowly. According to the National Park Service, Muldrow Glacier normally moves 3 to 11 inches per day. During this current surge, the glacier is moving 30 to 60 feet per day, which is changing the face of the glacier.

When the glacier is flowing normally, or in its quiescent phase, the crevasses — those deep open cracks in the glacier — are fairly regular.

“When it moves at this pace, 10 to 20 meters per day, it’s basically chaotic flow,” Adema said. “We’re getting the glacier moving very quickly, the ice moving very quickly, it’s adjusting very quickly so you get very large crevasses, very sharp edges to the glacier, and many parts surrounding the surging ice are totally impassible.”

“Normally, the Muldrow’s really stagnant so it’s usually really debris-covered, barely has any cracks in it especially that lower section,” said Chad Hults, a regional geologist with the National Parks Service. “And now that it’s surging, it’s just cracking up like crazy because it’s moving so much.”

The reason glaciers surge isn’t well understood. Scientists with NPS and the University of Alaska Fairbanks are taking this opportunity to study this one.

“We’ve installed a bunch of time-lapse cameras and a couple GPS units on the glacier,” Hults said.

He said the GPS units on the glacier, are “taking data every 30 seconds so we can get the really minute details of the glacier flow throughout the surge.”

The fact that Muldrow Glacier is fairly close also helps.

“This is one of the more accessible glaciers to surge so we have repeat satellite imagery,” Adema said. “We have time-lapse cameras, sound stations to listen to the sounds that may accompany a glacier. The first people visiting who sat on this glacier while it’s surging have reported you can hear it underneath you moving. It’s moving feet per hour. It’s exciting … It’s a great opportunity on a glacier like this that has such history.”

Hults describes the process of surging as starting when the ice in the upper reaches of the glacier builds up and it reaches a point where the glacier can’t hold the heavy weight of all that ice, and the ice releases.

“It starts cracking up and water starts flowing to the base,” Hults said. “And once you get that water basically lubricating the base it kind of pseudo-floats the glacier and the whole thing starts moving and sliding on its base.”

Glaciers tend to start surging during winter, as the Muldrow Glacier did. Based on seismic signals recorded nearby, the activity began in December 2020.

“If we look back at history, the 1957 surge,” Hults said. “It ended in August. We should expect it (the current surge) to go to sometime mid-summer.”

Hults has worked on Muldrow Glacier before.

“The most exciting part of this was being part of some baseline, pre-surge studies back 19 years ago, back when I was an intern with the National Park Service up in Denali. To be up on the glacier back then it was all stagnant and covered with debris. It was easy to walk across,” Hults said. “And then to go out there just a couple of weeks ago and see the entire glacier completely shattered up, and having ice walls that are 50 feet high and fresh ice just cracking and falling down on the edges. It was just a spectacular sight. Professionally, it was really exciting to be back and actually see it happen, waiting for it to happen after 19 years.”

“This is one of those great sort of spectacles of nature,” Adema said. “It’s a natural process that doesn’t happen very often and when it does, it’s really exciting to see the earth change that quickly.”

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