Utah’s Rock Glaciers May Harbor a Gigaton of Subterranean Ice

Scientists at the University of Utah have developed a novel measurement technique suggesting that the state’s rock glaciers may harbor up to a gigaton of ice. A gigaton equals a billion metric tons, a cubic kilometer, or 815,000 acre-feet of water. In fact, if estimates are correct, Utah’s rock glaciers represent about a third of the entire annual input of water into the Great Salt Lake.  

Rock glaciers’ footprints are clearly evident with satellite imagery, or even while on foot in alpine terrain across the intermountain Western U.S. However, measuring them isn’t as straightforward as with clean ice glaciers. 

While a regular glacier is a smooth sheet of open ice, a rock glacier is a moving mixture of ice and talus stone hidden beneath a thick outer “blanket” of loose scree. Radio Echo Sounding – essentially a form of radar – is the gold standard for measuring normal glaciers. But it relies on radio waves passing smoothly through clean ice and bouncing off relatively solid bedrock below. In a rock glacier, the internal structure doesn’t allow for a clean radio echo. Radar waves just hit embedded rock material and scatter.

A Novel Approach for Measuring Rock Glaciers

Geologists from the University of Utah wanted to test another measurement method that uses differences in gravitational pull between rock and ice. So former graduate student Bronson Cvijanovich headed to Timpanogos Rock Glacier in fall 2024. His haul to the talus fields above Emerald Lake included a state-of-the-art gravimeter. Over the course of six days, he collected gravity readings at 232 locations at 25-meter intervals across the glacier.

The gravimeter detects gravitational differences between the rock comprising Mount Timpanogos and the lower-density ice. “There is a large contrast in mass density between the rock that makes up Mount Timpanogos and the much lower-density ice that is in the rock glacier adjacent to it,” said Michael Thorne, a geophysicist overseeing the study. “When we measure the gravitational acceleration over the rock glacier, we see a larger decrease in that gravitational acceleration as we make measurements over areas with thicker ice.”

After the initial field experiments, the team headed back to the lab for some heavy lifting. They needed to corroborate differences in gravity due to sun and moon positioning, and Mount Timpanogos’ terrain, latitude, and elevation. “We spent months of computation time doing the imaging with our new techniques,” says Thorne.

Glaciology professor Leif Anderson, who oversees the research alongside Thorne, added: “There’s a lot of ice that’s hidden in Utah’s mountains. When we are high in the mountains and walking across loose rocks or rubble, you don’t realize there could be 120 feet of ice buried beneath your feet.”

The Geologist’s Findings

Eventually, the team’s measurements concluded that the rock glacier likely holds enough water to fill the largest Pyramid at Giza. Interestingly, they also calculated that the so-called “rock” glacier is actually mostly ice. “Timpanogos Rock Glacier is surprisingly ice-rich. It is 83% ice and 17% loose rock,” says Cvijanovich.

Ultimately, the researchers used their measurements from Timpanogos Rock Glacier to establish a relationship between its surface area and the volume of ice hidden beneath it. From that data, they extrapolated that Utah’s glaciers hold 1 gigaton of ice. Meanwhile, the world’s estimated 50,000 rock glaciers hold about 48 gigatons in total.

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Why Do Rock Glaciers Form?

Contrary to what you’d expect, rock glaciers are not remnants of ice age glaciers. Those melted off by about 12,000-13,000 years ago. Today’s rock glaciers have formed over thousands of years since the end of that glacial maximum.  

Rock glaciers also form in more temperate environments than normal glaciers. Generally, they require some level of permanent snow cover in their accumulation zone. Too much, though, and you have a clean ice glacier. Over time, rockfall from surrounding peaks buries snow and eventually pushes it underground, where it consolidates into ice, much like a normal glacier. Typically, a steep mountainside or cliff produces a constant supply of talus rock through frost weathering.

Also akin to normal glaciers, the mass eventually begins to move downhill under its own weight. Notably, rock glaciers move much more slowly than normal glaciers. However, like normal glaciers, a small terminal lake can often form at the foot of a rock glacier. 

Rock glaciers are important water sources, especially in Utah and Colorado, where they continue to provide cold, nutrient-rich freshwater long after the winter’s snowpack has dwindled. They are also somewhat less sensitive to a warming climate, as a thick layer of boulders insulates them. However, if permanent snowfields in the accumulation zone disappear, a rock glacier will eventually enter a negative mass balance and retreat. 

• Related: A California Frozen in Time: Understanding Glaciers in The Golden State

The Intermountain West is a Landscape of Rock Glaciers

Utah is home to 836 known rock glaciers, though this is almost certainly an undercount, as researchers primarily rely on satellite imagery to identify them. Nearly all of Utah’s ice formations exist in the Wasatch and Uinta Mountains, though there are also a few in the La Sal Mountains near Moab.

Meanwhile, neighboring Colorado is home to an estimated 3,500 rock glaciers. If you’ve ever climbed a 13’er or 14’er in the late summer, when conditions are ideal, you may have traversed over one. They’re usually a mess of jagged scree and loose talus. And if you’ve stopped to take a drink at a high mountain stream and been pleasantly surprised by the cold, fresh water…well, you may have been nourished by the meltings of a rock glacier.

Mountains Are Losing Their Permafrost

Rock glaciers are a form of mountain permafrost. This summer, melting permafrost has become not just a talking point among niche mountaineers and geologists. It’s entered into the mainstream news cycles, with the Tibet and Nepal landslide, as well as constant rockfall in the European Alps that has closed major mountaineering routes.

Disappearing glaciers have been the big story over the last few decades. And normal ice glaciers are the canaries in the coalmine. They’re sensitive to subtle climatic shifts and are among the first features to reflect changes in the natural world. However, as temperatures continue to warm, heat will make its way deeper into mountain rock. Eventually, our alpine rock glaciers will begin to shrink. We probably won’t see Nepal-style disasters in the Western U.S., but we could see increased rockfall. We may also see diminished freshwater stream flows in late summer. That could have an impact on sensitive riparian zones that rely on cold, nutrient rich water.

• Related: How a Landslide Triggered a Biblical Flash Flood in Tibet and Nepal