The swings look beautiful on the images of the NASA satellite “Landsat 8” over the bottom of the northern Central Siberian mountains in Russia. A Twitter post in February 2020 drew the American space agency’s attention to the structures and prompted them to carry out more detailed analyzes, because the pattern not only looks good, its creation puzzles experts.
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The research has become a scientific detective story, writes NASA about a year later in a press release. It also published the satellite images in it. At 66 degrees north latitude, striped patterns snaked around the hills of the Central Siberian Mountains, the organization said. The shape of the pattern obviously follows certain rules.
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On steeper hills, the strips form tight loops that wind down from the top of the bumps. On the descending path towards smaller rivers and the large Markha river, they become increasingly pale and finally disappear in lower elevations. Why this is so cannot be clearly answered, according to NASA. The answers varied depending on the expertise of the experts questioned.
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Game between thawing and freezing ground
One cause could therefore be the interplay between freezing and thawing soils. The Central Siberian mountainous region is located in the Arctic Circle with air temperatures mostly below freezing. Most of the year, the soils are frozen to depths of tens or even hundreds of meters. The area with the Schlieren is 90 percent of the year under permafrost, writes NASA.
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But in between the ground thaws and starts to move, especially on slopes where gravity pulls the masses down. Experts suspect that the striped patterns could have emerged on the hills. In studies According to NASA, this has so far only been documented to a much lesser extent than the satellite images from Russia now show.
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Geomorphologists therefore suspect another reason for the pattern, in which the thawing and freezing of the subsoil also play a role: For example, in areas with permafrost, so-called gelisoles are more common – soils that are frozen at depths less than two meters even in summer . The frost slows down the breakdown of organic matter by bacteria and fungi.
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Dead plant remains are only slowly broken down. If the ground partially thaws in summer, the process accelerates in places. Gelisols therefore consist of a mixture of darker and lighter soils with different levels of organic and mineral sediments. When freezing and thawing, these layers mix and slide into one another in a vertical pattern.
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In the summer, the pattern comes into its own, explains NASA (see GIF above). Lichen, bushes and mosses grew preferentially on the soil, which was richer in organic constituents, and strengthened the drawings on the ground. So far, however, the explanation has only been a hypothesis, it has not been proven.
Even in winter, the drawing is particularly eye-catching because the snow remains on flat areas of the furrows while it slides off the side walls. This makes the latter appear darker (see slide below).
Shaped by melting snow and rain
There is a third possible cause for the pretty drawings on the mountain landscape: geologists, the pattern is reminiscent of layers of sedimentary rocks, so-called layer cake formations. This describes structures that have been exposed in a characteristic form through erosion.
On the slopes of the Central Siberian Mountains, when the snow melts and when it rains, large masses of water move downwards and drag parts of the subsoil with them into deeper canyons. At the same time, the subsurface is eroding due to tensions that arise during freezing and thawing. The furrows created in this way may then appear in the documented pattern from space.
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The furrows look like small canyons, explains Walt Meier, ice specialist at the American National Snow and Ice Data Center. Horizontal stripes in the pattern probably consist of different layers of sediment. The theory could also explain why the pattern becomes weaker in the direction of the river banks: This is where sediments that have loosened elsewhere over the past million years are likely to be deposited.
However, this genesis has not been definitively confirmed either.
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