Researchers develop a new method for analyzing rock glaciers


Researchers develop a new method for analyzing rock glaciers

Drone image of the Sourdough Rock glacier flowing from the summit of Sourdough in August 2021. Credit: Michael Christoffersen

Standing on a rock glacier is what Tyler Meng imagines it would be like standing on Mars. The glacier’s barren, wrinkled landscape looks like silly putty that has sagged under gravity, providing little evidence that a frozen, debris-laden behemoth lurks beneath the surface.

Rock glaciers are so named because unlike pure glaciers, they are a mixture of frozen water, sand, and rock. They are generally found at the base of steep mountainsides or cliffs that have slowly dropped rock debris, which then mixes with glacier ice Re-freeze and thaw. Rock glaciers are also found on Mars.

Meng – who follows a PHD degree in Planetology at the University of Arizona, with a minor in geosciences–he is the lead author of a study in Glaciology Journal describes a new method for determining ice thickness in glacier rocks and the ratio of ice to debris, allowing for more precise measurements of these glaciers than was previously possible. Ming and his advisor and co-author Jack Holt, professor of planetary and geosciences at the University of Arizona, used this information to create maps of four rock glaciers in Colorado, Wyoming and Alaska.

Their work and future work using this method will allow scientists to better understand the water resources on both Earth and Mars, as well as just how resilient this type of buried ice is to the changing climate on both planets.

More than just snow

Rock glaciers are hidden and isolated by debris above the ice, and their movement is affected by the rocks trapped within.

“You can think of rocks as an insulating blanket,” Meng said. “After a certain thickness, the insulation essentially stops the melting process, allowing the ice to be preserved and move slowly or flow down the valley at altitudes and temperatures where clean ice might completely melt.”

Pure glaciers and rock glaciers can move across the landscape – very slowly. However, debris in rock glaciers causes them to flow more slowly than in glaciers, because the inclusion of rock makes them more solid. They are also smaller and thinner than pure glaciers, being only a few miles long, a few hundred or thousands feet wide, and between 50 and 200 feet thick. Glaciers, by contrast, can be several miles long and thousands of feet thick.

To gather the information needed to map and characterize these hidden behemoths, Meng, Holt, and other UArizona students and collaborators climbed the rugged mountainous terrain of the western United States, lugging computers, battery packs, and radar antennas on their backs. They navigated steep landscapes with loose boulders ranging in size from grains of sand to houses.

“Standing on a glacier covered in debris is very surreal, because it is located in this arid area on the mountainside, and each rock glacier seems to have its own personality,” said Ming. “Each has a slightly different type of rock that provides the debris, and the canyon’s geometry dictates its look and feel.”

Using two different antenna configurations, the researchers used ground-penetrating radar to measure the speed of the radar wave and the angle at which the wave reflected from the Earth’s interior. In the same way that humans have eyes that can see in three dimensions, two antenna configurations allowed the researchers to better calculate the dimensions of the rock iceberg. They also estimated the ice-to-rock ratio at each survey site using the radar wave velocity.

“In the process, we’ve made the most accurate estimates of ice rock geometry and composition to date,” Meng said.

Researchers develop a new method for analyzing rock glaciers

Lead author and graduate student Tyler Meng stands with radar equipment on Sourdough rock ice, Alaska in August 2021. Credit: Stefano Nerozzi

From Earth to Mars

Understanding rock glaciers on Earth is important because they are intrinsic water reservoirsMeng said.

“Our research gives us a better idea of ​​the total water budget in mountainous regions, where major rivers have headwaters,” he said. “Snow is an annual accumulation that covers an entire area, while rock glaciers are a more local, but permanent water reservoir that actually stores water for what may be hundreds to a few thousand years.”

The researchers continue their analysis to understand signs of past climate change in rock glaciers and how these glaciers may have evolved through past climate changes.

“By obtaining a map of debris thickness and ice concentration, we can basically determine the ability of rock glaciers to withstand the effects of a warming climate compared to clean glaciers,” Meng said.

Other scientists have also identified rock glaciers on Mars by their curly, putty-like flow pattern, even before radar data detected them.

Martian rock glaciers are still not well understood, Meng said, but it is known that they are typically found between 30 and 60 degrees latitude in both hemispheres and are much older than Martian polar ice.

“These Martian rock glaciers are potential targets for water resources on Mars as well, because they are actually quite large compared to those on Earth, like hundreds of metres,” said Ming. “It’s also more accessible than polar ice because spacecraft wouldn’t have to change orbits as much as they would if they landed on a pole, which takes a lot more fuel to get to.”

One of the big challenges for scientists is determining the thickness of the surface rocks that cover glaciers on Mars. If there are 30 feet of rocks and debris on the rough Martian terrain, it may not be feasible for astronauts to attempt to reach the ice in order to water resourcesMeng said.

“Our goal is to use these rock glaciers on Earth as a counterpart to operations on Mars,” Meng said. “By mapping the debris thickness patterns on Earth, we are trying to understand how this debris thickness can also vary on Mars. Also, by recognizing the differences in flow parameters between clean ice and debris-rich ice, this will aid in the simulations in the case of Mars as well. “.

Going forward, Holt’s research group continues to make similar measurements using surface radar while collecting new data using drones. The drone-driven data collection will help the group gain a more complete understanding of rock glacier flow and subsurface properties, while also testing new geophysical methods that can be used in future exploration of Earth and Mars.

more information:
Meng et al., Formation and structure of rock glaciers from radio wave velocity analysis with dip reflector correction Glaciology Journal (2022). DOI: 10.1017/jog.2022.90

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University of Arizona

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