Decoding the mysterious stone that can float for years, even sinks and floats again

Pumice stone, a stone made of magma erupted from volcanoes, can float on the water for many years, even after sinking, can still float again. Recently, scientists have found a mechanism to help them have this strange ability.

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Pumice floats on the water after a volcanic eruption.

Pumice stone has many tiny holes filled with air and linked together. Normally, this will make the pumice sink easier because if water flows into one of the holes on the outside, they will quickly enter other holes and cause the stone to sink. But in fact there are some pumice stones after being submerged and sinking for a while again floating again.

Close to pumice stones can be floating on the surface of the sea for many years.

To understand the cause of this strange phenomenon, scientists dipped foam stones over water, then coated them with a wax layer. Finally, they took X-rays of the stone to see the distribution of water and air contained in the small holes.

In the end the secret of a rock that was not submerged was deciphered. The answer is due to the surface tension of the water inside the stone through the air trap mechanism. Specifically, the surface tension of water causes the amount of air in the small holes to not escape and is "confined". The smaller the size, the more pronounced the surface tension effect. This is also the reason that water spiders move on water without sinking or how rain drops cannot flow through small holes between stretched yarns on the umbrella.

The pumice strip on the sea.

Kristen Fauria from the University of California-Berkeley in the US said: " Many air bubbles are as small as human hairs wrapped together. This makes surface tension very effective. big " .

After a while, the air in the small holes gradually diffuses to the outside, causing the water to flow in and the stone sinks. But when the weather warms, the temperature rises, the amount of air remaining inside the expansion pushes the water out, and causes the rocks to float again.

These findings are expected to explain the mechanism of giant pumice blocks being formed. Some giant pumbles of up to 1m width were created during underwater volcanic eruptions, while most of the other rocks were about the size of an apple.