Denali Park glacier surging 65 feet a day, threatening summit route

 glaciere in a snow-covered mountainn valley
The Muldrow Glacier on March 17, 2021. (National Park Service)

The 34-mile-long Muldrow glacier is the largest on the north side of the Alaska Range, visible from the road into Denali National Park. But as the glacier surges down toward the McKinley River, the view is changing.

The glacier is moving about 65 feet a day right now, over 100 times faster than its non-surge speed of 16 centimeters a day.

The last time the Muldrow glacier surged was in 1956-57, when it advanced over 4 miles in a few months, leaving behind a now dirt and vegetation-covered area of ice.

Denali National Park Science and Resources Team Leader Dave Schirokauer recently flew onto the glacier. The surge has churned up its surface, he said and is expected to end with a large release of water in June.

“[There’s the] potential for a very intense outburst flood. There’s just masses of water trapped under that glacier, to lubricate that surface to the extent where it can surge at this rate,” he said. “The reason the surge ends is because that trapped water finds a path out.”

Schirokauer said the water will flood the McKinley River but is not expected to impact any populated areas, which are far downstream. He said the Muldrow surge is being closely monitored by scientists and an array of instruments deployed on and along the glacier.

“You have a soundscape station out there on the edge, and we have time-lapse cameras and the whole story is on our brand new Muldrow surging glacier website,” he said.

According to the National Parks Service, surging glaciers are rare, but Denali’s extreme topography makes them more common around its peak.

“Right now, the toe of the glacier is pushing into old, stagnant ice. So it might break that up and be a pretty dramatic change in the scenery,” Schirokauer said.

The Muldrow appears to operate on a roughly 50-year surge cycle, Schirokauer said. That’s dictated factors such as the geometry of the glacier, the underlying bedrock and the hydrology of meltwater flowing under and around the ice.

Schirokauer said the glacier’s non-surge speed was originally measured by famed mountaineer Bradford Washburn back in 1976.

“He deserves some credit here because he is the only person that measured the rate of movement on the glacier during its quiet phase and so that reference condition that he captured in 1976 is awesome right now, like we have a story to tell about how fast it normally goes and how fast the ice is moving during the surge,” he said.

Prior to Washburn’s establishment of the West Buttress as the preferred route to climb Denali, the Muldrow was the most popular path for mountaineers. It’s still attempted by a few every year — but Schirokauer said the surge has made that route impassable.

“There were a couple of parties that were planning on using the Muldrow as their climbing routes in attempting the summit this year. Those folks are being encouraged to change their plan,” he said. “My hunch is that the historic route on the Muldrow won’t be climbable for many years to come.”

He said the Park Service soon hopes to begin uploading real-time images of the Muldrow glacier’s surge.

This story previously misspelled Dave Schirokauer’s last name