Note to readers • This story is made possible through a partnership between The Salt Lake Tribune and Grist, a nonprofit environmental media organization.

Utah’s mountains are hiding a ton of ice — perhaps a billion tons of it.

Those ice troves are locked inside “rock glaciers,” which are hidden under a shell of rocky scree that insulates the ice and slows its melt. Scientists are now getting a better grasp on the amount of water those glaciers hold, and what they could mean for a warming and drying West.

“They’ve been studied for quite a long time,” said Leif Anderson, an assistant professor in the Department of Geology and Geophysics at the University of Utah. “The real puzzle is how much ice is actually in them.”

Researchers have documented around 51,000 large rock glaciers across the globe, and about 10% of them are found in the Western U.S. Utah alone is home to roughly 800 large rock glaciers.

Now, research on one of Utah’s most prominent rock glaciers is helping scientists put a number on that hidden ice.

Using their findings from the Timpanogos Rock Glacier, researchers estimate that Utah’s rock glaciers could collectively hold about 1 billion tons of ice.

“We can’t say for sure,” Anderson said, “but that’s the guess.”

That’s around 815,000 acre-feet of water, enough to support the basic annual needs of about 1.6 million Utah households.

Climate change is raising the stakes for understanding just how much ice is in Utah’s rock glaciers, Anderson said.

“There’s a water crisis,” Anderson said. “It’s an arid state. It’s time to start understanding the things we maybe don’t know about where water is stored in Utah.”

How the glaciers form

In Utah, there are around 3,000 rock glaciers that range in size from a typical house to the equivalent of 20 football fields, Anderson said.

Rock glaciers form after rocks collapse and land on snowfields, shielding them from heat and evaporation. They’re prevalent in the West because of the region’s steep mountain slopes — which both provide shade and are more prone to rockfall — along with winters that typically produce a lot of snow.

“We have evidence of them forming as far back as 14,000 years ago in Utah,” Anderson said.

The shells protecting these glaciers can be several feet thick, meaning hikers in the Uinta, Wasatch and La Sal mountains may walk over them and not realize what’s below. But geologists have honed their ability to identify them using aerial photographs and satellite imagery.

“It sort of looks like honey flowing,” Anderson said, “but it’s rocks.”

One of the most accessible rock glaciers in Utah is the Timpanogos Rock Glacier, towering high in a bowl-shaped mountain basin about 5,000 feet above Provo.

“There are actually Salt Lake Tribune articles from the early 1900s [or] 1920s that talk about crevasses on this body,” Anderson said. “It has lore.”

The “glacier” that locals identified was actually a snowfield. It has no crevasses like a traditional glacier. But those early Utahns were onto something. Timpanogos does hold an old, slow-moving body of ice — it’s just buried beneath rock.

Measuring the hidden ice

Researchers hiked to the Timpanogos glacier from August to October 2024. They first calculated how fast the glacier is moving down the slope.

“That’s an important piece of information we can also use to say ... how thick the ice must be beneath us,” said Michael Thorne, a geology professor at the U. “That speed depends on how thick that ice is.”

It moves at roughly 10 to 20 centimeters per year, depending on where they measured the glacier, Thorne said.

The geologists also sent electrical currents into the ground to map where ice was buried beneath the rock. Those measurements didn’t show how thick the ice was, so the scientists combined the sections that contained ice with the velocity measurements to calculate the glacier’s volume.

They found that the ice is about 61.6 feet thick on average and up to 150 feet deep in its thickest parts.

The Timpanogos Rock Glacier, they found, contains enough frozen water to fill about 600 Olympic swimming pools. The scientists published their latest findings Wednesday in the Journal of Geophysical Research: Earth Surface.

The U.’s research underscores the importance of these formations as the planet warms. They create microclimates in high mountain environments that provide a refuge for animals like the American pika along with insects and plants adapted to cold. Their springs and seeps support aquatic species threatened by extinction, the study notes.

“In really arid places,” Anderson said, “the melt from rock glaciers becomes increasingly important.”

The scientists still don’t know how much the Timpanogos Rock Glacier contributes to streamflows and water supplies used by people in the urban valley below. But the glaciers could become potential water sources for increasingly thirsty places like Utah with its booming population.

“It’s sort of an emerging reality,” Anderson said. “As things get hotter, you evaporate more, you lose more water to the atmosphere. Increasing whatever water sources we have is essential for the success of the state.”