This rock creates a shadow and changes the degree of sublimation of the surrounding ice.
Visit the Little Sea of Lake Baikal in Russia in the winter and you will probably see an unusual phenomenon: a flat rock on a thin base of ice, similar to the selection of Zen stones common in Japanese gardens. This phenomenon is sometimes called Zen Baikal Organization. The common explanation for how these formations form is that rocks take light (and heat) from the sun and melt the ice beneath them, leaving only a thin base to support. The water under the rock freezes again at night and it is said that wind can be a factor as well.
According to a new article published in the Proceedings of the National Academy of Sciences, two French physicists believe they have solved the mystery of how these structures form and that their solution has nothing to do with the thermal conductivity of rocks. Instead, they attribute the formation to a phenomenon called sublimation, where snow or ice evaporates directly into vapor without passing through the aqueous phase. In particular, the shadow created by the rocks prevents surrounding ice from accelerating faster, while distant ice sublimates faster. Many similar formations occur naturally in nature, such as hoodoos (the long, spindled structures that form within sedimentary rocks over millions of years), fungal rocks, or rocky outcrops. eroded soils) and glacial streams (large rocks that sit uncertainly on a narrow base of ice) but the underlying mechanisms for their formation can be quite different.Read more Mathematicians may have discovered the secret of how "rock forests" are formed
For example, as we reported last year, a team of applied mathematicians from New York University named "rock forests" common in certain parts of China and Madagascar , these pointed rock structures, such as the famous rock forest in China's Yunnan province, are the result of solids dissolved in liquids in the presence of gravity, creating natural convection currents. On the surface, these rocky forests look almost like "penitents": ice columns formed in the very dry air found in the glaciers of the Andes. Charles Darwin showed his way through the snow-covered fields of Banets in 1839 during his March 1835 voyage to the city of Mendoza, Argentina, on the paths of hurricanes from Santiago, Chile. Physicists have managed to reconstruct artificial versions of penitents in the laboratory. But repentance and stony forests are completely different in terms of the mechanisms that participate in their formation. The spikes of the rocky forest are circled by streams that do not play an important role in the formation of penitents.Advertising
Some physicists have suggested that when sunlight evaporates snow directly into vapor, repentance (sublimation), small crowns and depressions are formed, and sunlight is trapped in them, resulting in excess heat that creates deeper cavities and the curved surfaces in turn act as a lens. And increase the sublimation process. An alternative proposal adds an additional mechanism to account for the constant individual distances of the repenters: a combination of vapor diffusion and heat transfer that creates a steeper gradient, and thus a higher sublimation rate.Zen / rocks in nature, in the small sea of Lake Baikal (a, b); in the laboratory (C); In numerical simulation (D). (a) A photograph taken by A. Zima. (b) A photograph taken by A. Yanariv. Nicholas Tablet / Nicholas Plion
In the case of the Baikal Zen rock formations, according to co-authors Nicholas Tablet and Nicholas Plion, this process is similar to the sublimation hypothesis of penitents. CNRS in Lyon, France. Earlier this month, they published a somewhat related study in Physical Review Letters on the natural formation of glacier streams (a rock supported by a narrow column of ice). They were able to produce small-scale industrial refrigerator tables in a controlled environment and found two interactions that control the beginning of the formation of a natural refrigerator table. The heat flow causes the cap to sink into the ice. For a larger mantle with lower thermal conductivity, the lower heat flow is due to the fact that the temperature is higher than the surrounding ice and a table is formed.
In this latest study, Taberlet and Plihon sought to discover the mechanisms underlying the natural formation of Zen Baikal structures. "The rarity of this phenomenon is due to the scarcity of thick, flat, and snowless ice layers that require long-lasting cold, dry weather," the authors wrote. "Climatological records show that thawing is almost impossible, and instead climatic conditions (wind, temperature, relative humidity) seek sublimation, which has long been a feature of Lake Baikal."
So the researchers tried to test their hypothesis by reproducing this phenomenon in the lab. They used metal disks as experimental analogues of the rocks and placed the disks on the surface of blocks of ice in a commercial drying machine. This tool freezes the material, then reduces pressure and adds heat, so that the frozen water is heated. The higher reflectivity of metal discs compared to rock prevents the discs from overheating in the cooler chambers. Both aluminum and copper discs produced zen-like structures, although copper has nearly twice the thermal conductivity of aluminum. The authors concluded, therefore, that the thermal properties of the rocks are not an important factor in this process. "Far away from the rock, the amount of sublimation is controlled by scattered sunlight, while the proximity of the shadow it creates prevents the sublimation process," the authors wrote. "We show that the rock acts only as a canopy, its shadow preventing sublimation, thus protecting the underlying ice, resulting in the formation of the base." Taberlet and Plihon also found that depression or depression around the base is caused by infrared radiation far from the rock (or disk) itself, increasing the overall rate of sublimation in its vicinity.
Despite the similar shape of the two formations, they are quite different from the process that leads to the glacier streams. In the case of refrigerator tables, the canopy effect is only a minor factor in the underlying mechanism. "Glacier streams appear on lower glaciers when atmospheric conditions cause the ice to melt rather than sublimate," the authors wrote. "They form in hot weather while ice stays at 0 degrees Celsius, while zen rocks form in air that is cooler than ice." In the world, because ice sublimation caused repentance on Pluto and affected the formation of landscapes on Mars, Pluto, Ceres, Jupiter, Saturn and many more comets. The authors conclude: "Indeed, NASA's Europa Lander project is seeking to obtain a biological signature on Jupiter's icy moon, where differential sublimation may threaten Lander stability, and this must be fully understood." p> DOI: PNAS, 2021. 10.1073/pnas.2109107118 (about DOIs).
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