For the first time in history, scientists have observed how bubbles or lighter particles are formed in the sand. This feature, which is generally seen in liquids, attracted the attention of scientists working on the sand.
Sand grains alone are solid. On the other hand, when they come together with other grains, they act like liquids. For example, when you take your sand into your palm, it flows through your fingers, and while walking on the beaches, your feet lightly sink into the sand. Such materials are called granular materials.
Although granular materials act like fluids, physicists have not fully solved the structure of these materials. The reason why stratification or lighter materials are gathered together in the sand is not known exactly.
There is a phenomenon called Rayleigh Taylor instability in liquids. As a result of this instability in fluid dynamics, liquids of different densities are layered. For example, olive oil is less dense, so the water goes down as it rises. In the supernova explosions, the gas that is stuck and heated breaks out by breaking down the denser upper surface.
Such an event was not previously observed in granular materials, but scientists from Columbia University and ETH Zurich discovered a similar situation.
Researchers have discovered that vibration and upward gas output in granular structures such as sand form a similar structure to Rayleigh Taylor.
The flow of air or gas from the larger and less compact grains is easier, while the effect of the gas flow is less in the denser and smaller grains. For this reason, it provides stratification of sands or granular materials. This leads to instability like RT instability. In order to control this situation, the researchers did both experiments and checked with the computer as a calculation.
The team found other strange points during the work. For example, air flow also forms stalagmite-like structures.
The results of this research will be used to understand what happened in seaside seas in earthquakes, to pave the way for more efficient use of granular materials used for energy and construction and for geological researches.
The research was published in PNAS. You can also see a very enjoyable video showing the movements of the sands below.