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."
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.
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 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.Rock glaciers 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.
Estimating the water contents of the world's rock glaciers
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..
The 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.
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.
