Hikers crossing the boulder fields on Mount Timpanogos have no idea they're walking on top of 150 feet of solid ice. University of Utah geologists just proved it's there — and measured exactly how much.

  • 1 billion tons of ice estimated hidden in Utah's rock glaciers
  • 836 rock glaciers mapped across the state
  • 83% of Timpanogos Rock Glacier's mass is pure ice, just 17% loose rock
  • 150 feet — the ice's thickest point, buried under a blanket of rubble

How you weigh a glacier you can't see

Rock glaciers look like nothing more than piles of rubble sliding slowly downhill. Underneath, though, they can hide enormous quantities of ancient ice, insulated from the sun by a "carapace" of loose rock.

Geology graduate student Bronson Cvijanovich spent six field trips hauling a sensitive gravimeter up a five-mile trail to Timpanogos Rock Glacier, above Emerald Lake. He took gravity readings at 232 separate spots, each 80 feet apart, mapping tiny differences in gravitational pull between rock and ice.

Ice is less dense than rock, so patches with more buried ice produced a measurable dip in gravity. After correcting for the sun, moon, terrain, and elevation, the team built a 3D map of the glacier's interior using Bayesian statistics — the same statistical approach used to interpret medical scans.

"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," said glaciology professor Leif Anderson.

The result: Timpanogos Rock Glacier alone stores enough frozen water to fill 600 Olympic swimming pools — roughly the volume of the Great Pyramid of Giza.

Why this ice matters for a thirsty state

The bigger surprise is where this ice came from. A companion study found Utah's rock glaciers aren't leftovers from the last Ice Age. They formed gradually afterward, as rockfalls buried persistent snow patches high in mountain cirques, protecting it from melting for thousands of years.

Some are still growing today. "This is not just ice that's left from the time of Lake Bonneville and mammoths... Timpanogos rock glacier is still adding ice today!" Anderson said.

Because the rock cover insulates the ice from a warming atmosphere, researchers describe rock glaciers as unusually climate-resilient water stores — a quality that matters a great deal in an arid state like Utah. Using their new ice-to-surface-area formula, the team estimates the world's 50,000 known rock glaciers collectively hold roughly 48 gigatons of water, with Utah's share equal to about 815,000 acre-feet.

Both studies, published in the Journal of Geophysical Research, grew out of research at the University of Utah, with support from the U.S. Geological Survey, the National Science Foundation, and the U.S. Forest Service.

For a state that depends heavily on mountain snowpack, a previously invisible billion-ton reservoir is good news worth measuring precisely — and now, for the first time, scientists finally can.