Home North pole ice Castner Glacier ice cave gushes with meltwater as it slowly collapses

Castner Glacier ice cave gushes with meltwater as it slowly collapses

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Experts urge visitors to ice caves to be careful about opening – and discourage trying to cross Castner Creek

The Castner Glacier ice cave, off Richardson Road near Black Rapids, attracts around 8,000 people a year. But federal officials and a University of Alaska professor are advising hikers to be careful around the ice cave, as it gushes out with meltwater and is slowly collapsing.

North Pole residents April, Allison and Chuck Hohnbaum were among those who ventured on the trail to Castner Glacier on July 4.

Chuck and Allison Hohnbaum descended from the North Pole on a hot, sunny day last week to do the 45-minute hike to the terminus of Castner Glacier and check out the ice cave there.

“I’ve been here several times in the winter, where you can go into the cave,” Chuck said, “and we thought we’d give it a try during the summer.”

Hohnbaum and his wife, Allison, and sister, April, parked their rig with a dozen others during a stop at the Richardson Freeway bridge over melt-swollen Castner Creek at mile post 217 They said they did not hear there is a torrent of water several feet deep running through the cave, and it is slowly collapsing. But Allison says that didn’t deter them.

“No, we are super happy! ” she says. “It’ll be pretty cool to see it with the river gushing out of it.”

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A sign at the trailheads on the north and south sides of the creek advises hikers to be careful around the ice cave.

It indeed shoots out of the roughly 10ft by 20ft opening at the entrance to the cave, and it ejects rocks and chunks of ice, some as big as a washing machine before they are transported downstream and do not melt. That’s why the Federal Bureau of Land Management has posted signs on the trail leading to the glacier urging hikers to be cautious when approaching the ice cave.

“You can still hike and see Castner Glacier. The area is not closed,” says Scott Claggett, spokesman for the Federal Office of Land Management. “We just want to make sure people are aware and safe.”

Claggett says this year’s wave of runoff and meltwater is the largest in recent memory. And that’s why a snow and ice expert from the University of Alaska Fairbanks urges caution for those visiting the cave, especially if they want to peek inside.

“People need to be very aware that any tunnel in the ice is temporary and there is a potential danger that it will collapse or rocks that are in the ice above will collapse,” says Matthew Sturm, a professor of geophysics at the UAF Geophysical Institute who directs his Snow, Ice and Permafrost Group.

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The current flowing out of the cave pushed large chunks of ice like this onto the south bank of Castner Creek, about 100 feet from the mouth of the cave.

Sturm says the meltwater created the ice cave, and now it’s collapsing it.

“Water entering the glacier from the sides and above tends to want to work under the glacier below to enter a single channel,” he said in an interview last week. “And it emerges from the tip of the glacier, the terminus, leaving a tunnel.”

Sturm says the dynamic process is going on in all of Alaska’s glaciers, especially those east of the Alaska Range, which are all melting and retreating. He says so-called “down waste” is being accelerated by global warming and unusually hot summer weather. But he says the gravelly material the glacier has piled up on its terminus is helping to slow the melting.

“All the glaciers I know of in the Alaska Range have this debris at the bottom,” he said, “and it actually saves them from the worst of climate change because it serves as a protector and insulation against those warmer temperatures.”

Sturm also discourages those ascending to the glacier from crossing Castner Creek, both because of the high flow and because of the chunks of ice and other debris it carries.