It's true - some rocks can stay on the water for years. And now scientists know how this happens and why in the end they drown.
X-ray studies at the National Laboratory. Lawrence Berkeley, USA, helped scientists unravel this mystery by scanning samples of lightweight, fragile and porous volcanic rocks known as pumice.
The amazing buoyancy of these rocks - which can form kilometer-long "pumice rafts" in the ocean - will help scientists track underwater volcanic eruptions.
And, besides that, data on the buoyancy of pumice will allow you to find out how species spread across the planet. Pumice is rich in nutrients and serves as a carrier for plants and other organisms. Also, floating pumice can be dangerous for boats, as the ash mixture clogs the engines.
Although scientists knew that pumice could float due to pockets of gas in the pores, it was not known how these gases stay inside the pumice for a long time. After all, if, for example, a sponge absorbs enough water, it will sink.
Some pumice stones in the laboratory sank in the evening and rose to the surface during the day. To understand the processes. occurring in these stones, the team covered the areas of pumice in contact with water with wax.
The researchers found that the process of trapping gas in pumice is due to the phenomenon of surface tension, a chemical interaction between the surface of water and air, which acts like a thin skin. The same process allows insects and lizards to walk on water.
The team also found that percolation theory helps to understand how liquid enters a porous material. She also explains the process of trapping gas in pumice. And the gas diffusion theory, which describes how gas molecules search for areas of low concentration, makes clear the ultimate loss of gases that causes rocks to sink.
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