Scientists have for the first time tracked how one of the deadliest volcanic hazards moves over time.
Pyroclastic density currents are searing hot clouds of ash and gas released by volcanoes; they travel up to 724 km per hour.
Their speed and intense heat make it nearly impossible for humans to observe - anybody who got close enough to monitor one would be killed, researchers said.
But scientists from the University of Leicester have developed a novel way of reconstructing how one of these currents flowed, 'Planet Earth' reported.
Their technique showed for the first time that instead of flowing radially out from the volcano and covering everything in their path, these currents move initially in one direction, but that this direction then changes.
"In the magma chamber under a volcano the chemistry of the magma at the top is different to the chemistry at the bottom. During an eruption these chemical zones are erupted at different times, so if something was erupted at the beginning it would show a record matching the chemical zone from the top of the magma chamber," said Dr Rebecca Williams, now of the University of Hull, lead author on the project.
"We realised that if I could find a chemical zoning in an ignimbrite I could use it as a proxy for time," said Williams.
The research looked at a deposit on the volcanic island of Panetelleria left by one of these pyroclastic density currents during an eruption 45,000 years ago.
"The Green Tuff on Panetelleria was huge. It was much bigger than the ones that buried Pompeii and Herculaneum," said Williams.
"It was very hot when it was deposited which means it welded and turned into a green volcanic glass that covers the entire island. It hasn't really been weathered, which means it is incredibly well preserved. It is an incredible exposure," said Williams.
The chemical structure of this deposit, called the Green Tuff ignimbrite, varies from the bottom to the top, in a similar way to the variation in a magma chamber.
The team matched the variation seen in the Green Tuff with the same layers in the magma chamber to assess at what point during the eruption they flowed.
They were surprised to discover that the circular deposits often left by these currents didn't mean that they flowed out in a circle out from the eruption.
The study was published in the journal Geology.
