What is often called the lowest-elevation glacier in the lower 49 states is formed by avalanches off the steep north face of Big Four Mountain. Because of a lack of snow, the glacier is likely to shrink to its lowest volume in years.

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The Big Four Ice Caves owe their existence to a quirk of topography.

It’s rare for a permanent mass of snow and ice to form at an elevation of only 2,000 feet. But the caves lie at the base of a towering, 4,000-foot cliff on the north face of Big Four Mountain. Throughout the winter, avalanches roar down a chute in the steep face, creating a massive pile of ice, rock and snow that usually meets the definition of a glacier.

In fact, it’s considered the lowest-elevation glacier in the United States, outside of Alaska.

In the spring, water cascading off the mountain flows under the ice and melts out an opening. As the weather warms, the opening expands and a large chamber forms — luring unwary hikers like those caught in Monday’s collapse.

The size of the snow and ice pile fluctuates widely, but this year it’s likely to shrink to its smallest volume in the last decade, said geologist Mauri Pelto, of Nichols College in Massachusetts.

“It didn’t get any snow at all this winter; no avalanches fell down on it,” said Pelto, who leads a long-term project to monitor glaciers across the Northwest. “That’s the first time I’ve seen that.”

As early as March, Pelto and his colleagues were certain this would be a treacherous summer at the caves.

“This year, it didn’t even get cold enough for the caves and tunnels to stop expanding in the winter,” he said. “They were poised to collapse right from the start of the melt season.”

The glacier also shrank dramatically between 2002 and 2005, during a series of poor winters. At one point, it was only about 20 feet thick and could no longer even be classed as a glacier, Pelto said. But it started rebuilding in 2006. By 2009, he estimated the maximum thickness at 180 feet and the length at more than 1,200 feet. And enough of the mass was blue ice to put it back in the glacier category.


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“Most glaciers don’t change in thickness very rapidly, but this one does,” Pelto said. “But it may lose the distinction of being a glacier this summer.”

Even if the glacier shrinks dramatically for several years, the unusual circumstances at Big Four mean that it can quickly bounce back after a year or two of heavy snowfall.

That’s very different from Washington’s other, famous ice caves, which are gone for good, Pelto said.

Carved by running water, the Paradise Glacier Ice Caves at Mount Rainier National Park were a popular tourist attraction from the 1930s through the 1980s. For years, the famed mountaineering twins Lou and Jim Whittaker guided groups through the labyrinth, using road flares to light the way and cast a dramatic glow on the ice.

At least five people died in the Paradise caves over the years, including a man who caused a partial collapse in 1915 by poking at the ice ceiling.

By the early 1990s, though, the lower glacier had melted away.