Thu. May 26th, 2022

In rocky, frosty landscapes, specific stone patterns can end up forming – this is how human hands have formed them, but without a gardener being near them. A new study shows how these formations can be created with needle ice – tips that rise from the ground and are formed with groundwater.

The researchers used a combination of laboratory experiments and computer models to show how needle can move small stones and soil particles into patterns and push them from below to slightly change their position.

Because needles are more likely to form and bloom on bare spots of the earth, the surrounding rocks gradually consolidate in the areas around these spots – creating some spectacular patterns that can extend a considerable distance across the landscape from Norway to Hawaii.

“That kind of selective growth involves interesting feedback between the size of the rock, the moisture in the soil and the growth of ice needles,” says geologist Bernard Hallet of the University of Washington.

This idea of ​​needle-producing patterns from stone dates back decades, but here the researchers used their own experiments to see how the formations actually came together and then developed a computer model that could simulate the same process.

The experimental setup was a flat square of wet soil a little over 0.3 meters in size with stones placed evenly on the surface. Researchers then put the setup through 30 freeze-thaw cycles, representing the changing temperatures day and night.

As you can see from the resulting videos (including the one above), patterning can start happening pretty quickly and within the 30 freeze-thaw cycles. The concentration of the rocks, the slope of the earth and the height of the ice needles all affect how the patterns are formed.

“The videos are pretty striking, and they show that the ice is just coming up, and in a single cycle, it pushes up rocks and moves them a little to the side,” Hallet says. “Because of these experiments and the ability of the individuals involved to analyze these results, we have much more tangible, quantitative descriptions of these features.”

The researchers also linked their study with models of phase separation – the concept of two different parts coming out of one can be useful for analysis of cell structure, gravitational fluids, ecological systems and more.

This field of research also goes beyond our own planet: Scientists are also working to analyze some of these patterns seen on the surface of Mars, which may reveal both what is on the surface and what is happening in the Martian environment.

stone experimentsTwo computer models predict stone distribution based on initial concentration. (Li et al., PNAS 2021)

What’s more, because the needle and the patterns it makes are so closely linked to local temperatures, the team believes that the shift of rock formations over time can help us understand how the planet responds to rising temperatures.

“Our study highlights phase separation theory as a source of important insights into studying soil patterns in cold regions and their potential value in signaling important changes in soil conditions with the warming climate,” the researchers write in their published paper.

The research has been published in PNAS.


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