An international team of scientists has uncovered the secrets of the speed of pyroclastic flow that brings death and destruction following a volcano eruption.

A pyroclastic flow is an extremely hot mixture of rock fragments and gases that travel rapidly downslope. Sometimes, the liquidized material can reach the speed of up to hundreds of miles per hour and incinerate everything in its path.

The Roman city of Pompeii was famously annihilated by pyroclastic flow when Mount Vesuvius erupted in 79 A.D. A car cannot outrun a pyroclastic flow.

It is one of the leading killers following a volcanic eruption, but scientists are still unaware of how the pyroclastic flow moves rapidly and cover great distances despite the friction between volcanic materials it carries and the ground, until now.

In a study published in the journal Nature Science, researchers revealed that pyroclastic flow can move fast and far because it is protected with a cushion of air that protects it from friction. The new findings can help scientists predict the movement of pyroclastic flow and save communities in its path.

Laboratory-Made Volcano

To observe the movement of pyroclastic flow safely, the researchers recreated the currents inside a laboratory using materials from an actual volcanic eruption in New Zeland 2,000 years ago. They heated up the debris and dropped them onto a high-friction slope. The researchers captured the process using a high-speed camera.

They found that the volcanic materials quickly separated into two layers, one was an ash cloud on the upper layer while the other was a denser base layer. The denser base layer, where high-pressure volcanic material accumulates, is the key to a pyroclastic flow's speed. The air is forced down due to the high pressure, creating a frictionless layer that allows the material to move rapidly.

Saving Lives

Understanding the pyroclastic flow can help authorities identify the hazards around volcanoes and create better plans to save communities in case of an eruption. The researchers said that their findings can also be applied to other natural calamities, including avalanches and landslides.

"Currently, we are working on trying to understand how these volcanic flows generate enormous damage potential and how they maintain to do so during runouts over complex terrain," said Gert Lube of Massey University in New Zeland and one of the authors of the study. "Part of the results of the published work is used currently in an international exercise of volcanologists to intercompare and validate computational volcanic hazard models."