Unlike conventional glaciers, rock glaciers appear as piles of rock that obscure large masses of unaccounted-for ice. Rock glaciers are common in the Wasatch and Uinta ranges, even appearing on the Colorado Plateau in the La Sal Mountains near Moab.
Now, University of Utah geologists are bringing one of Utah's largest rock glaciers, located under the towering, iconic summit of Mount Timpanogos near Salt Lake City and Provo, into sharp focus. Two new studies document how Timpanogos Rock Glacier formed and how much ice it contains. By measuring minute differences in gravitational pull between rock and ice, the team created a novel technique to image the 3D ice body within a large rock glacier.
Timpanogos Rock Glacier stores enough frozen water to fill 600 Olympic swimming pools or 1.5 million cubic meters. That is also equivalent to the volume of the largest pyramid at Giza in Egypt, according to Bronson Cvijanovich, a former graduate student in the Department of Geology & Geophysics.
"Timpanogos Rock Glacier is surprisingly ice rich. It is 83% ice and 17% loose rock, said Cvijanovich, the lead author of one of two studies overseen by geophysics professor Michael Thorne and glaciology professor Leif Anderson.
The ice hiding under our feet
"There's a lot of ice that's hidden in Utah's mountains," Anderson said. "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."
Timpanogos Rock Glacier was selected for study because of its easy access from a trailhead and long history of what was known as "Timpanogos Glacier," really a rock glacier the whole time. Still, it's a five-mile hike in with an elevation gain of 3,500 feet.
Cvijanovich led field campaigns to Timpanogos Rock Glacier hauling sensitive instruments, including a state-of-the-art gravimeter, to the ice buried above Emerald Lake in the fall of 2024. Over the course of six forays, Cvijanovich took gravity readings at 232 spots, separated by 25 meters (~80 feet) in a grid atop the rock glacier. In 2026, Cvijanovich completed his master's degree at the U and now works as a field gravimetry technician for a Utah geothermal company.
The gravimeter measures density differences between rock and ice, enabling scientists to calculate the 3D shape of the buried ice body. "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," Thorne said. "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."
Once the gravity observations were collected, they still needed to be corrected for differences in gravity due to the position of the sun and the moon, the location's terrain, latitude, and elevation. After these corrections, the research really broke new ground. The team developed a novel method for imaging the internal ice of the rock glacier in 3D using Bayesian statistics. "We spent months of computation time doing the imaging with our new techniques," Thorne said.
Seeing beneath the surface using gravity
Rock glacier footprints can be outlined with satellite imagery, but the 3D shape, depth, and ice they obscure is harder to reveal. For such measurements, scientists need instruments that can "see" what is hidden under the rocky rubble, like the way a CT scanner can image bone and tissues inside the human body. Similarly, these U researchers created a virtual map of Timpanogos Rock Glacier's interior that is 150 feet deep at its thickest.
Since this glacier appears as a rubble pile to those walking across it, it is confounding how the ice gets into the rock glacier in the first place.
The other new study by these U researchers explains this conundrum. Rock glaciers exist below steep-walled mountain valleys or cirques that frequently shed rocks. "In the Wasatch, the mountains themselves are eroding and burying the snow, and that's why the rock glaciers exist," Anderson noted. The researchers wrote a new mathematical model that shows how rock glaciers gain mass: rockfalls bury persistent snow in the upper parts of rock glaciers.
This work shows that years with high snow totals, low summer temperatures, and larger rockfalls lead to ice addition. This is why some years the entire rock glacier surface is rubble and in other, increasingly rare years, you see rock-covered snow sticking around into September. The team has documented more than 70 debris-on-snow patches in the Timpanogos Rock Glacier cirque.
Despite climate change, rock glaciers appear to be adding ice
This second study shows that Utah's rock glaciers are not remnants from the Ice Age (which reached its peak 21,000 to 18,000 years ago), but rather water stores that formed over the thousands of years after the Ice Age glaciers melted away.
"This is not just ice that's left from the time of Lake Bonneville and mammoths. We don't yet know which rock glaciers are still adding ice today outside of a few dozen under active research. Some of these rubble fields hold ice today, but some have melted out," Anderson said. "But Timpanogos rock glacier is still adding ice today!"
Timpanogos Rock Glacier is one of 836 rock glaciers documented in Utah using satellite imagery. These researchers used their findings on Timpanogos rock glacier to identify a relationship that provides a scale between a rock glacier's surface area and the volume of ice beneath. Using this new relationship, they estimate that the world's 50,000 known rock glaciers hold 48 gigatons of water. Equal to 1 billion metric tons, a gigaton is the equivalent of a cubic kilometer of water, enough to fill 400,000 Olympic swimming pools. Utah's rock glaciers may hold a 1 gigaton, or 815,000 acre-feet of water, the researchers estimated.
"Rock glaciers flow downhill just like a glacier or river, but the important distinction here is that the thick carapace of loose rock actually protects and hides the ice, making these climate-resilient water storage sites that may still be adding frozen water. From a water resource standpoint, it is really important, especially in a warm and arid state like Utah," Cvijanovich said.
Cvijanovich's paper, titled "The internal ice content of Timpanogos Rock Glacier, Utah, USA from 3-D Bayesian inversion of gravity data," was published in the Journal of Geophysical Research. The other paper, titled "Mass Addition to Timpanogos Rock Glacier: Debris‐ Covered Snow and the Importance of Interannual Variability in Headwall Erosion and Climate," appears in Geophysical Research Letters, with Isaiah Davies, an undergraduate at Stanford University and visiting summer researcher at the University of Utah in 2023, as lead author.
Co-authors on these papers include research assistant professor Surya Pachhai, geophysics graduate student Ivan Tochimani-Hernandez and geophysics professor and gravity specialist Tonie van Dam, as well as scientists at the Utah Geological Survey, Middlebury College and Utah Valley University. The U's Center for High-Performance Computing and the U.S. Forest Service provided valuable support. Funding came from the U.S. Geological Survey, National Science Foundation, University of Utah's Wilkes Center for Climate Science & Policy, the U's Office of Undergraduate Research and the Summer Program for Undergraduate Research.
Banner photo of Mount Timpanogos by Bronson Cvijanovich
