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Into caverns of ice

Posted: February 25, 2011 - 8:47am
A hiker walks through a large ice tunnel formed by icebergs at the face of the Mendenhall Glacier early this week.  Klas Stolpe
Klas Stolpe
A hiker walks through a large ice tunnel formed by icebergs at the face of the Mendenhall Glacier early this week.

Ice caves. They are illusive, mysterious and as striking as a fine diamond. They are also deadly. It’s fair to say, however, that most things worth seeing in this world carry an inherent level of danger.

Most are drawn to the unknown. Hence, it’s not surprising that Juneau locals and visitors seek out these frozen caverns which lead into the depths of Mendenhall Glacier.

On Monday, footprints could be seen leading to the entrance of a cavern flanked by two entrances near the center of the face of the glacier. The floor was a frozen Mendenhall Lake and the walls and ceiling seemed to be formed by two icebergs which had fused together over the course of the winter.

The walls of the roughly 50-foot tunnel were scalloped, which indicates erosion by air currents. Snow had drifted onto the floor and a lone videographer, Skip Gray, captured images of the azul ice.

According to Dave Bunnel, who has caved in areas of Alaska and all over the world, caves formed completely in ice are properly termed glacier caves, as that is where they typically occur. Ice caves, by contrast, are caves of any type that contain speleothems — such as stalagmites or stalagites — made of ice.

Glacier caves almost always form from flowing water entering the glacier through cracks or crevasses, which are then enlarged over time, both by erosion and melting. In addition, glacier caves may also serve as conduits for water through glaciers. Caves such as these are dynamic and change from year to year.

Roman Motyka, who worked as an associate professor of geology and geophysics at the University of Alaska Southeast, was interviewed for an article on this topic in 2007. He said caves form as a glacier moves over a disorder in the ground surface and it detaches itself from the floor. The base layer re-contacts with the ground layer forming striations, thin parallel lines made up of sediment, which refreezes to the base of the glacier.

It’s true glacial ice caves are spectacular. It’s also true they can be deadly. Glaciers, especially the Mendenhall, are always on the move — even in the winter. Lori Craig, a U.S. Forest Service interpreter at the Mendenhall Glacier Visitor Center, has told stories of calving events that have turned the surface of a frozen Mendenhall Lake into a “slushy.” Caves in the depths of the glacier a subject to the same instability, and huge ice boulders can break loose unexpectedly.

Exactly how long the glacier will support the formation of the ice caves is pure speculation. The less stable a glacier, the less likely it is to stay still long enough to allow the cave’s formation. Craig said the Mendenhall Glacier is calving at about 200 feet per year.

Matt Heavner, an adjunct professor of physics at the University of Alaska Southeast, surmised the caves will be around for a while. He believes that there is less calving and greater stability in the wintertime due to the lower water volumes.

“It is a very dynamic situation and in terms of safety, I don’t like to joke about it, but it’s probably safer to go in the ice caves then for a pedestrian to cross a street in the city, but that’s because there is a lot more cars and a lot more people in the city, whereas there is not that many people going in ice caves.”

Heavner advocates the buddy system, implying one should rethink entering the caverns solo.

Dangers can be minimized by planning ahead, carrying gear appropriate for the weather, ice self-rescue tools and going with knowledgeable, well-seasoned guides.

To read a full article on the ice caves of Mendenhall Glacier, go online to: http://www.juneauempire.com/stories/090907/out_20070909001.shtml.

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