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October 6, 2021
Stone circles in Svalbard, Norway. Each circle is approximately 10 feet or 3 meters in diameter. New research is providing insight into how these features form in rocky and frost-prone landscapes.Bernard Hallet / University of Washington
Nature is full of repeating patterns that are part of the beauty of our world. An international team, including a researcher from the University of Washington, used modern tools to explain the repeating patterns of stones that form in cold landscapes.
New to study, published Oct. 5 in the Proceedings of the National Academy of Sciences, uses experimental tools to show how ice needles growing at random on frozen ground can gradually move rocks in regular, repeating patterns. The team, based primarily in China and Japan, uses a combination of new experiments and computer modeling to describe these striking features with new theoretical knowledge.
“The presence of these amazing patterns that develop without any human intervention is quite striking in nature,” said the co-author. Bernard Hallet, UW Emeritus Professor of Earth and Space Sciences and member of the Quaternary Research Center. “It’s like a Japanese garden, but where’s the gardener?”
Lines of stones in Hawaii. Repeated freeze-thaw cycles create lines when the stones are on steeper sloping ground.Bernard Hallet / University of Washington
Hallet specializes in the study of patterns that form in polar regions, high mountains and other cold environments. One of the reasons for the patterns is needle ice cream. As the temperature drops, the moisture in the soil turns into spikes of ice crystals that protrude from the ground.
“When you step out into the garden after a frosty night and feel a little crackle under your foot, you are probably walking on needle ice,” Hallet said.
As needle ice forms, it tends to lift soil particles and, if there are any, small stones. More needle ice can form on patches of bare soil compared to areas covered with rocks, Hallet said. The ice needles will move the remaining stones slightly in the more bare area. Over the years, the stones begin to cluster in groups, leaving the bare plates mostly without stones.
“This type of selective growth involves interesting feedbacks between stone size, soil moisture, and ice needle growth,” Hallet said.
Stone mazes in Svalbard, Norway. Maze patterns form where the stones are on a gentle slope. New research is providing insight into how these features form in rocky and frost-prone landscapes.Bernard Hallet / University of Washington
Hallet had previously reviewed another scientific paper by the first author Anyuan Li, formerly at Shaoxing University and now at Tsukuba University in Japan. The two have started a collaboration that combines Hallet’s long-standing expertise in investigating patterns in nature with Li and his collaborators’ experience in experimental science and computer modeling.
Principal author Quan Xing Liu at East China Normal University uses fieldwork and laboratory experiments to understand self-organizing patterns in nature. For this study, the experimental setup was a flat square of moist soil just over 1 foot on each side (0.4 meter) that began with stones spaced evenly across the surface. The researchers carried out the experiment over 30 freeze-thaw cycles. By the end of this period, regular models had started to appear.
“The videos are quite striking, and they show that the ice has just come up and in one cycle it lifts rocks and moves them slightly to the side, ”Hallet said. “Because of these experiences and the abilities of the individuals involved to analyze these results, we have much more tangible quantitative descriptions of these characteristics.”
Other experiments examined how the pattern changes depending on the concentration of stones, the slope of the ground, and the height of the ice needles, which is also affected by the concentration of stones. Based on these results, the authors wrote a computer model that predicts the patterns that will appear depending on the concentration of stones on the frost-prone surface.
Two different computer models predict the long-term distribution of stones on frozen ground based on the initial concentration of stones. The left column begins with 20% stone coverage, creating islands, shown here in white; the middle rows have 30% and 40% stone coverage, which creates mazes and worm-like shapes; and the fourth column is 80% stone coverage, which gives no pattern. The right column shows 20% stone coverage on slightly sloping ground; stones tend to form lines.Li et al./PNAS
The other co-authors of the new study are Norikazu Matsuoka of the University of Tsukuba; Fujun Niu at South China University of Technology; Jing Chen and Wensi Hu at East China Normal University; Desheng Li at Shanghai Jiao Tong University in China; Johan van de Koppel at the University of Groningen in the Netherlands; and Nigel Goldenfeld at the University of California at San Diego.
The research was funded by the Tibetan Second Plateau Scientific Research and Expedition Program; the Japanese Society for the Promotion of Science; the National Foundation of Natural Sciences of China; Chinese Academy of Sciences; and the China Scholarship Council.
For more information, contact Hallet at [email protected] or Liu to [email protected]. See also a Chinese press release: http://news.sciencenet.cn/htmlnews/2021/10/466403.shtm
Days): Bernard Hallet • College of the Environment • Department of Earth and Space Sciences
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