The Castner Ice Cave, a popular hiking destination along the Richardson Highway near Delta Junction, has partially collapsed. The front part of the cave, located at the foot of the Castner glacier, has disappeared, but the rear 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 they were unsure when the collapse happened, but added that “we expect it to have happened in the last week with a warm weather”. The collapse was not entirely unexpected as “glacial landscapes are constantly changing”, although Graham said they had not studied Castner Glacier or made any predictions about how it might change.
Glacial caves such as 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 the ice melts, the water sinks to the bottom of the glacier. It often flows into crevices and digs into the ice, forming a channel of water running through the ice, much like a pipe.
Caves collapse when the ice on top becomes too thin to support the structure. Intuitively, this often happens during the summer months due to the hot weather.
Truffer wasn’t sure how long Castner’s Cave had existed, but said it had been there for at least several decades, and he was fairly confident that Castner’s Cave had already collapsed. “It’s a very dynamic environment,” he says of the glacial landscape.
Everywhere, glaciers are retreating every year, causing the caves at their base to collapse. It’s completely normal for caves to fall, Truffer said. “It’s almost inevitable,” he added.
After a flat and easy walk of about a mile from the road, the cave has become a popular tourist attraction in recent years. About 8,000 people have visited the cave in the past year, Graham said. She added that interest in the cave has grown over the past five years, but has increased significantly over the past two years.
Although there is too much water flowing through the cave to enter in the summer, at this point there is enough formation left that people can probably go back inside the cave in the winter.
Truffer warned visitors to exercise caution around the cave entrance due to rock slides. Even if people don’t enter the cave, they can be hit by rocks falling from above.
“Sliding rocks are a bigger hazard than melting ice,” Truffer said.
