The Castner ice cave, a popular hiking destination along the Richardson Highway near Delta Junction, has partially collapsed. The front portion of the cave, located at the base of Castner Glacier, is gone, but the back part is still standing.
The first report that the cave collapsed came from hikers on Wednesday. Bureau of Land Management Field Manager Marnie Graham said that they do not know exactly when the collapse occurred but added that “We expect that it occurred this past week with hot weather.” The collapse was not entirely unexpected because “glacial landscapes are always changing,” although Graham said they have not studied the Castner Glacier or made predictions about how it might change.
Glacial caves such as the Castner ice cave are formed by water, explained Martin Truffer, a professor of physics at the University of Alaska Fairbanks and a member of UAF’s Glacier Group. When ice thaws, water runs to the bottom of the glacier. It often trickles into crevasses and hollows out ice, thereby forming a water channel running through the ice, somewhat akin to a hose.
Caves collapse when the ice on top becomes too thin to support the structure. Intuitively, this often occurs in the summer months due to warm weather.
Truffer was unsure how long the Castner cave has existed but said it has been there for at least several decades, and he was fairly confident that the Castner cave has collapsed before. “It’s a very dynamic environment,” he said of the glacial landscape.
Glaciers everywhere are retreating each year, causing caves located at their bases to collapse. It is very normal for caves to fall in, Truffer said. “It’s almost inevitable,” he added.
At the end of a flat and easy roughly one-mile walk from the road, the cave has become a popular tourist attraction in recent years. Approximately 8,000 people visited the cave in the past year, Graham said. She added that interest in the cave has been growing for the past five years but dramatically increased over the last two years.
While there is too much water running through the cave to enter it in the summer, at this point enough of the formation remains that people will likely be able to go inside the cave again in the winter.