Natural arches and bridges, columns, vaults and other exotic sandstone formations fascinate with their extraordinary shape and absolutely incomprehensible stability. They have always been a source of surprise and curiosity for many generations of scientists, and ordinary people sometimes took these statues for "greetings" from ancient civilizations or even aliens. In general, it was clear that their main architects were wind, water and sun, but until recently, the reason for their non-trivial forms remained a mystery.
The first solid experimental and theoretical study of the mechanisms of erosion that underlie the formation of natural arches was carried out three years ago by mathematicians from Charles University in Prague. They found that shapes arise from the unique self-organization of sand grains within sandstone strata. Scientists hypothesized that natural erosion removes primarily unstressed material, which is "ineffective" in terms of load distribution. The reason for this behavior lies in the law of dry friction - the stronger the particles of material are compressed by adjacent layers of material, the more difficult it is to separate them.
Skoltech researchers were fascinated by the idea of their Prague colleagues, and they continued to study the question of the mechanisms of the formation of such structures. They decided to look at the phenomenon of erosion as a process of shape optimization (shape optimization is now widely used in modern industry, when engineers and architects improve the shape and structure of structures they erect, where both strength and light weight are needed). And then, to test their idea, the scientists created a mathematical program describing the process of wind erosion, and with its help they built an arch using a computer model of the sandstone layer. The sandstone model consisted of many almost unrelated cubes, acting on neighbors with a certain force. If this force exceeded a certain value, then the wind could not move the "cube" from its place,otherwise, it disappeared from the reservoir after a certain period of time, RIA Novosti reports.
Experimenting with this model, Russian scientists confirmed the idea of their Czech colleagues and revealed several physical principles that explain how columns and arches are born. In their most general form, they showed that the wind plays the role of a kind of "computer" trying to shape the sandstone layer into such a shape that the minimum amount of elastic deformation energy accumulates inside it, gradually and accidentally removing the weakest elements from the structure.
Initially, this process proceeds quickly, but after several hundred years, when the shape of a column or arch is already approaching the ideal, erosion slows down sharply, since almost all "cubes" begin to cling to each other with great force. Thanks to this, real mountain arches and columns can exist for millions of years in an almost untouched form.
Such conclusions are important not only for engineers and geologists, but also for people looking for traces of extraterrestrial life. Now, as Russian mathematicians emphasize, such structures, which, for example, can be discovered on Mars, in principle, cannot be considered traces of extraterrestrial civilizations.
