Visit the Little Sea of Lake Baikal in Russia during the winter, and you’re likely to see an unusual phenomenon: a flat rock balanced on a thin base of ice, resembling a pile of zen stones common in Japanese gardens. This phenomenon is sometimes referred to as Baikal Zen training. The typical explanation for how these formations occur is that the rocks capture light (and heat) from the sun and this melts the ice below so only a thin base remains to support it. The water under the rock regenerates at night, and it has been suggested that wind may also be a factor.
Now, two French physicists think they have solved the mystery of how these structures form, according to a new article published in Proceedings of the National Academy of Sciences — and their solution has nothing to do with the thermal conductivity of the stone. Instead, they attribute the formation to a phenomenon known as sublimation, where snow or ice evaporates directly into vapor without passing through an aqueous phase. Concretely, the shadow cast by the stone hinders the sublimation rates of the surrounding ice in its vicinity, while the more distant ice sublimates at a faster rate.
Many similar formations occur naturally in nature, such as headwear (the long, thread-like structures formed over millions of years in sedimentary rocks), mushroom rocks or bedrock (the base was eroded by strong, dusty winds) and glacier tables (a large stone sitting precariously atop a narrow ice cushion). But the basic mechanisms by which it is formed can be completely different.
For example, like We reported last yearA team of applied mathematicians from New York University has studied “stone forests” common in parts of China and Madagascar. These sharp rock formations are like the famous stone forest In China’s Yunnan Province, as a result of the dissolution of solids in liquids in the presence of gravity, which results in natural convection flows.
On the surface, these stone forests look just like “penitents“: Snow-covered ice plumes forming in extremely dry air have been found high up in glaciers in the Andes. The penitents were described by Charles Darwin in 1839 on an expedition in March 1835 during which he made his way through snowfields covered with penitents on the way from Santiago, Chile, to the Argentine city of Mendoza. Re Synthetic copies of repentants in vitro. But penitents and stone forests are actually quite different in terms of the mechanisms involved in their formation. Stone forest points are carved by flows which do not play a large role in the training of penitents.
some physicists I suggested that the repentant form when Sunlight vaporizes snow directly into vapor (sublimation). Small ridges and troughs are formed and sunlight is trapped in them, creating additional heat that etches even deeper troughs, and these curved surfaces in turn act as a lens, accelerating the sublimation process even more. a alternative suggestion It adds an additional mechanism for calculating the peculiar periodic spacing of repentants: the combination of vapor diffusion and heat transfer results in a very steep temperature gradient and, therefore, a higher sublimation rate.
In the case of the Baikal Zen rock formations, the process appears similar to the sublimation hypothesis of penitents, according to co-authors Nicolas Taberlet and Nicolas Plehon of CNRS in Lyon, France. Earlier this month, hmm A somewhat related study was published In Physical Review Letters on the natural formation of glacial streams (a rock supported by a thin column of ice). They were able to produce small-scale artificial ice tables in a controlled environment and discovered two competing effects that controlled the onset of ice table formation.
With smaller stone caps with higher thermal conductivity, geometric amplification of heat flow causes the cap to sink in ice. For a larger lid with lower thermal conductivity, the reduced heat flow comes from the fact that the lid has a higher temperature than the ice around it, forming a table.
In this latest study, Taberlet and Plihon wanted to explore the mechanisms underlying the natural formation of Baikal Zen structures. “The rarity of this phenomenon stems from the scarcity of thick, flat, snowless ice sheets, which require long-lasting cold, dry conditions,” the authors wrote. “Weather records show that thawing is almost impossible, and instead, atmospheric conditions (wind, temperature, relative humidity) favor sublimation, which has long been known to be characteristic of the Lake Baikal region.”
So the researchers tried to reproduce the phenomenon in the lab to test their hypothesis. They used metal disks as experimental stone analogs, and placed the disks on the surface of blocks of ice in a commercial freeze dryer. The tool freezes the material, then reduces pressure and adds heat, so that the frozen water heats up. The higher reflectivity of metal discs compared to stone prevented the discs from overheating in the freezer and dryer chambers.
Outside of earth
Both aluminum and copper discs produced Baikal Zen configurations, although copper has nearly twice the thermal conductivity of aluminum. The authors concluded that the stone’s thermal properties were not a critical factor in this process. “Away from the stone, the rate of sublimation is subject to diffuse sunlight, while the shadow it creates in its vicinity hinders the sublimation process,” the authors wrote. “We show that the stone acts only as a canopy, the shadow of which interferes with sublimation, thus protecting the ice below, creating the base.”
This was then confirmed by numerical modeling simulations. Taberlet and Plihon also found that the cavity or depression surrounding the base is caused by far-infrared radiation emitted by the stone (or disk) itself, which improves the overall near-sublimation rate.
This is quite different from the process that leads to ice streams, despite the similar shape of the two formations. In the case of icy streams, the canopy effect is only a minor factor in the underlying mechanism. “Ice streams appear on low-altitude glaciers when weather conditions melt rather than allow ice,” the authors wrote. “They form in hot air while ice stays at 0 degrees Celsius, and zen stones form in air that is cooler than ice.”
Understanding how these formations occur naturally can help us learn more about other things in the universe, where ice sublimation produced penitents on Pluto and influenced the formation of landscapes on Mars, Pluto, Ceres, Jupiter’s moons, and Saturn’s moons. And many comets. The researchers concluded that, “Indeed, NASA’s Europa Lander project aims to search for biosignatures on the ice-covered moon of Jupiter, whose surface differential sublimation could threaten the stability of the probe, and this must be fully understood.”
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