In the Wasatch mountains near Salt Lake City, Utah, a popular hiking trail winds up through aspen and spruce trees to reach White Pine Lake.
Scott Hotaling is marching up this familiar path, but passes by the lake. He continues uphill and, after crossing a mossy stream, starts picking his way through a field of boulders.
His goal is looming above: a steep, 80-foot-tall wall of what looks like loose rock.
This is the source of the lake’s water, a so-called rock glacier.
While the word “glacier” may conjure up images of white slopes and snowy expanses, rock glaciers are big masses of flowing ice that are covered up by, well, rocks.
These rubble-strewn glaciers have long been considered a “geomorphological oddity,” says Hotaling, but researchers are getting increasingly interested in them, as it looks like they will persist a lot longer on the landscape than surface ice in a warming climate.
“Because they are covered by all of this debris, they are insulated from ambient conditions and things like climate change,” says Hotaling, a mountain ecologist at Utah State University.
“These things actually seem to be holding steady amidst widespread ice decline,” he adds. “They give people a little bit of climate hope.”
Since rock glaciers store a massive amount of water, they could turn out to be a vital resource for arid states like Utah, where the main water supply, winter snowpack, has been gradually disappearing.
Ice hidden in plain sight
The western states are home to more than 10,000 rock glaciers, making these ice features about twice as common as typical glaciers and permanent snow fields.
Yet only a tiny fraction of scientists around the world who specialize in glaciers do any research on rock glaciers, says Hotaling.
“Rock glaciers are vastly understudied relative to their charismatic surface ice cousins,” he says.
The first discussions of rock glaciers in the scientific literature seem to date back to the early 1900s, when researchers described them in the San Juan Mountains of Colorado. They got the moniker “rock glacier” in a 1910 report on these features in Alaska.
Since then, however, the bulk of rock glacier research has been done in Europe. That’s likely because rock glaciers in the Alps are located much closer to people, who can be affected by falling debris.
One study there tracked a rock glacier in the Alps for about 70 years and found almost zero change in the total mass of its ice. Meanwhile, nearby surface glaciers were shrinking rapidly.
That European rock glacier did start creeping downhill faster, and some new research shows that rock glaciers across the U. S. are doing the same thing.
This suggests that rock glaciers are not totally immune to the effects of climate. Still, they appear to be far more resilient in terms of holding on to their ice.
Hotaling and some colleagues have recently done work in the Teton mountain range showing that regular surface glaciers there seem to be losing ice about seven times faster than neighboring rock glaciers. That’s why he thinks rock glaciers will eventually dominate the western mountain landscapes as other kinds of ice go away.
When he gives scientific talks, he asks audience members to raise their hands if they know what a rock glacier is. Hardly anyone does. Lots of hikers and skiers in the western mountains have probably gazed at rock glaciers without realizing what they were seeing.
White Pine Lake, for example, is surrounded by rock fields. Unless a person knew what to look for, it would be easy to miss the rock glacier’s tell-tale steepened front.
While rockslides have a scattered, flat appearance, the ice in rock glaciers holds rocks in place.
Rare and precious samples
“I would love to have a magic wand that I could wave over every rock glacier and immediately know how much ice was in it,” says Hotaling, gazing up at the front wall of the White Pine Lake glacier.
It’s hard to know how much ice it contains because rock glaciers can have rock mixed up with the ice. The inside of this glacier could look like a layer cake, with the icing on top being several meters of heavy rocks.
All that rock is what protects the glacier ice from warming, but it means scientists who want to study the ice have a hard time nabbing samples of it.
“We can’t just get up there and start moving rocks with our bare hands,” says Hotaling.
Occasionally ice will peek out between boulders. And standing between the rocks on top of the glacier can feel like standing in front of an open refrigerator, as the air feels distinctly colder.
Hotaling is carrying a chainsaw in his backpack. He quickly scouts across the top of the rock glacier, hoping to find a crevasse or naturally-occuring hole that might reveal the ice.
That’s how Matthew Morriss, a geologist with the Utah Geological Survey, managed to collect a rare sample of rock glacier ice here a few years ago. The way that snow had melted just happened to create a channel that went under the glacier, creating a deep hole.
The top of that hole went through a section of gravel and then, beyond that, there was “a big layer--as far as we could see down this dark hole--of really blue ice, glacier ice,” recalls Morriss.
He and a colleague chainsawed out a hunk of that ice and hauled it back down the trail in a cooler, eventually sending the precious sample to the National Science Foundation Ice Core Facility in Colorado.
As far as he knows, it’s only the second significant ice sample from a rock glacier in the United States. And he says there aren’t too many samples from European rock glaciers, either.
He’s planned a bunch of analyses to determine the ice’s age and how far back the different layers of ice were deposited. That could indicate how often rock glaciers get replenished.
That special spot where he found the exposed ice is gone now, as it’s filled in with rock. Hotaling isn’t lucky enough to find anything like it on this visit to the glacier. The chainsaw stays in his pack.
“I would like to hold some rock glacier ice,” says Hotaling. “It’ll happen. I know the ice is in there.”
Water water everywhere
However, the day does bring the opportunity to study the water in the stream beneath this glacier, which is a lot easier to access.
“Increasingly, there’s an interest and a recognition that the water coming out of rock glaciers might be really important for the future,” says Hotaling.
One recent study showed that rock glaciers “contain globally significant water stores.”
And research shows that rock glacier water can be a substantial fraction of the water in Utah’s mountain streams in the late summer.
In the stream downhill from the White Pine Lake glacier, Hotaling and research technician Kendall Becker check out their depth gauge and a temperature sensor. The water’s almost freezing—33 degrees Fahrenheit.
Hotaling can’t find a stick, so he uses his bare hands to mix a specific amount of salt in a bucket with water. He dumps the salty water in the stream, and the researchers track how long it takes to move past a sensor placed downstream, in order to measure the stream’s flow.
This work is part of their effort to better understand how much water comes out of rock glaciers, what’s in it, and what parts of the ecosystem depend on it.
Rock glaciers could also provide a kind of refuge for cold-loving fish and other creatures, like pikas, as well as be a dependable source of drinking water.
Morriss says over half of Salt Lake City’s drinking water comes from just a few canyons. They’re chock full of under-appreciated rock glaciers.
Take Little Cottonwood canyon, for example, the home of the White Pine Lake glacier.
“If you look at the area of the canyon, you know, something like 12% of the canyon is covered with rock glaciers,” says Morriss. “But nobody’s been talking about them. I just find that interesting and mysterious.”
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