Zoom in / Stone Forest (Shilin) ​​in Yunnan Province of China may be caused by dissolution of solids in liquids in the presence of gravity, resulting in natural convective flows.

There are many amazing geological formations in nature, from Giant Bridge In Ireland to Castleton Tower In Utah, the various processes by which such structures form are of long-term interest to scientists. A team of applied mathematicians from New York University turned their attention to the so-called “stony forests” common in certain regions of China and Madagascar. These are pointed rock formations, like the famous Stone forest In China’s Yunnan Province, it is the result of solids melting in liquids in the presence of gravity, which produces convective flows, according to the NYU team. They described their findings in A recent paper Published in the Proceedings of the National Academy of Sciences.

Co-author Lev Rystrov told Ars that his group in the NYU Applied Mathematics Laboratory became interested in studying stone forests (technically a kind of Karst terrainA rather indirect way. They used simulations and experiments to explore the interesting shapes that develop in landscapes due to a number of “shaping” processes, most notably erosion and melting.

He said: “We discovered for the first time the protrusions formed by melting when we left the candy in a water tank and returned later to find a tower that resembles a needle.” “Even graduate student, senior author Mak Hwang, accidentally injured himself when he was impressed with the figure. This drew us into the problem, and we were very excited when we realized the association with stone peaks and stone forests, which were totally vague in their evolution. Hopefully it tells our experiences. Simple origin story behind these shapes.

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In order to test their simulations in the lab, the team combined granulated table sugar, corn syrup, and water into molds to make single blocks and columns of hard candy (hard crack) – an approximation of the soluble rocks that would normally form a karst topography. The block template included arrays of metal upright rods to “seed” the porous blocks for closer approximation. They put these candy blocks and columns in a plexiglass tank filled with room temperature de-gased water – deep enough that the dissolved sugars settle to the bottom, far from the objects being tested. They captured the dissolving process by taking digital photos at one-minute intervals.

You can watch a lapsed video of the experiment below, where a melted mass of candy turns into a group of sharp spikes that resemble a layer of nails. The mass begins with an internal pore and is completely submerged underwater, where it melts and becomes a “candy forest” before collapsing.

This happens even in standing water. “We found that the melting process itself generates the streams responsible for sculpting the spike,” said Rystrov. Essentially, the metal melts – or, in our experiments, lollipop candy that acts as a “phantom rock” – and the surrounding liquid becomes heavy and then flows downward due to gravity. So our mechanism does not require any specific flow conditions or other external conditions or environmental conditions: The recipe merely involves hydrolysis in liquid and gravity. “

Restrov Et al. It indicates that a similar mechanism is at work in the formation of stony forests, only on a much longer time scale. Soluble rocks such as limestone, dolomite, and gypsum are submerged under water, as the minerals slowly dissolve in the surrounding water. The heavier waters then sink under the gravitational pull down, and the flows form gradually from a karst topography. When the waters recede, pillars and stony forests appear.

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On the surface, these stony forests look somewhat similar toPenitents“: Snow plumes of ice form in extremely dry air high in glaciers in the Andes Mountains. Some physicists You have a suggestion Be repentant Shape when Sunlight evaporates snow directly into vapor, without going through the water (sublimation) phase. Small peaks and troughs form, and sunlight is trapped inside, creating additional heat that digs deeper troughs, and those curved surfaces in turn act like a lens, which speeds up the sublimation process even more. that Alternative suggestion It adds an additional mechanism to account for the peculiar periodic spacing between the penitents: a combination of vapor diffusion and heat transfer that produces a steeper temperature gradient, and thus a higher sublimation rate.

Physicists were able to To recreate it Synthetic copies of penitents in the laboratory. But penitents and stone forests are actually very different in terms of the mechanisms that participate in their formation. “I think the similarities are somewhat superficial,” said Rystrov. Certainly, the process of ‘carving’ differs greatly in terms of the main thrusting effects. Basically, the ripples are largely carved by the streams, which I don’t think play a big role in the formation of penitents. ”

Sure enough, NYU researchers have achieved their results under ideal conditions – intentionally, according to the authors, it is best to define and describe the sharpening process, the underlying mechanism, and the mathematical structure. As a result, “this study reveals a minimal set of essential components for needle and nail bed decorations,” the authors write. In the future, they hope to further test this formation process under various environmental conditions in the laboratory, such as how precipitation and runoff, or burial under loose sediments, affect summit formation.

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DOI: PNAS, 2020. 10.1073 / Banas. 2001524117 (About DOIs).