Rock Glaciers Hide an Astonishing Amount of Ice Worldwide

It is easy to think of glaciers as enormous sheets of white ice shining beneath an open sky.

Yet glaciers do not all look like this.

Across mountain landscapes, another variety exists: rock glaciers. These landforms combine ice with rock, their frozen cores concealed beneath a tough layer of stones and boulders.

A new study in the Journal of Geophysical Research: Earth Surface shows that rock glaciers may contain an astonishing quantity of ice.

More than 51,000 rock glaciers have been recorded worldwide, including over 10,000 in the US.

Even so, their thick rocky blankets keep these ice formations largely out of view, meaning that many people may not realise they exist.

"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," says glaciologist Leif Anderson from the University of Utah.

How rock glaciers conceal their ice

This natural cover of rock protects the ice within rock glaciers, shielding it from surface heat and sunlight. However, it also makes the formations difficult for scientists to investigate.

A major obstacle to understanding rock glaciers has been calculating how much water ice they hold beneath the rocky rubble covering them.

For their latest research, Anderson and his colleagues devised a way to measure ice reserves in rock glaciers. They tested the technique at Timpanogos Glacier, located at the foot of Mount Timpanogos in Utah.

Conventional glacier imaging can use ground-penetrating radar. For rock glaciers, though, the method performs poorly because debris intermingled with the ice scatters radio waves and reduces image quality.

Instead, researchers can use a gravimeter, an instrument capable of detecting and mapping concealed underground masses.

"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," says co-author and geophysicist Michael Thorne.

"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."

Mapping Timpanogos Glacier in three dimensions

After gathering 232 survey measurements from locations around Timpanogos Glacier, the team created a new approach for producing a 3D image of its internal ice. Bayesian statistics and modelling methods were used to reconstruct the rock glacier's form, thickness and composition.

Their findings indicate that Timpanogos Glacier consists of about 83 percent ice and 17 percent rocky debris by volume. Across the rock glacier, the ice has an average thickness of 18.8 metres (61.7 feet).

In total, this rock glacier contains roughly 1.5 million cubic metres of ice, approximately the volume of the Great Pyramid of Giza, or around 600 Olympic swimming pools.

By mass, Timpanogos Glacier stores about 1.4 million tonnes (1.5 million US tons) of ice beneath its rocky exterior. But the researchers extended their analysis beyond this site.

Drawing on earlier studies examining the internal structures of other rock glaciers, they used the Timpanogos Glacier results to establish a method for estimating ice volume from a rock glacier's surface area.

Rock glacier ice reserves in Utah and worldwide

Their estimates suggest that Utah's 836 documented rock glaciers together contain around 1 billion tonnes (1 gigaton) of ice.

The western US holds nearly 12 billion tonnes, while rock glaciers around the world store about 48 billion tonnes of ice.

The method offers a remarkable new means of assessing the ice concealed in rock glaciers globally. As the researchers note, continuing to improve estimates for these vast formations is important.

"The need to quantify the water stored in these features is only increasing as glaciers respond to climate change and have the potential to transition to debris-covered glaciers and ultimately rock glaciers," the team writes.

"During periods of warming, rock glaciers can become destabilized and pose a threat to downstream infrastructure. Modeling these landforms in 3D can help to quantify their water stores and image their internal structure, allowing their impacts on local hydrology, ecology, and hazards to be better constrained."

The findings are reported in the Journal of Geophysical Research: Earth Surface.

This article was fact-checked by Rachel Garner and edited by Rebecca Dyer. Although we take pride in our process, we are only human. If you notice an error, please let us know.