Volcano errupting

University research into deadly volcanic pyroclastic flows features in Nature journal

Studies led by a PhD student at the University of Hull have uncovered new understandings of deadly volcanic pyroclastic flows.

Pyroclastic Density Currents are one of the most lethal volcanic phenomena, having killed over 90,000 people in the last 400 years.

Famously responsible for the destruction of Italian town Pompeii, the currents are a hot mixture of gas and volcanic particles which can travel down the slopes of a volcano at speeds exceeding 50mph.

Greg Smith, a PhD student at the University of Hull, has been studying the behaviour of Pyroclastic Density Currents.

Using laboratory modelling, his research has formed a new paper, titled ‘A bedform phase diagram for dense granular currents’, published in world-renowned journal Nature Communications.

Mr Smith said: “Our experiments involved creating currents using very small glass beads, with similar properties to volcanic particles.

“Once fluidised with compressed air in a flume tank, these currents are a good simulation of actual PDCs. We examined how they behaved under varying conditions in the flume tank, capturing their passage on a high-speed camera.

“This allowed us to make measurements of certain parameters over time and study how those parameters controlled how deposition from the currents occurred, and what the deposits looked like.

“This is an important step in better interpreting volcanic rocks in the field, which is essential for hazard mapping at active volcanoes.”

The eruption of Mount Vesuvius, in southern Italy, in 79AD is one of the best-known pyroclastic events in history.

The remains of over 1,500 people have so far been uncovered in the towns of Pompeii and Herculaneum, after a devastating surge wiped out all in its path.

Due to their hazardous and unpredictable nature, most of volcanologists’ existing knowledge of PDCs has been gained from interpretation of the rock deposits they leave behind.

A wide range of sedimentary structures occur in these deposits, allowing volcanologists to infer the physical mechanisms occurring inside of a PDC.

The latest study, led by Mr Smith, used an experimental flume tank to simulate highly-concentrated PDCs and examine their deposits.

The experimental structures they generated, however, were unexpected.

Mr Smith said: “The prevailing view in volcanology is that these types of currents form homogenous, rather uniform deposits with no interesting sedimentary structures, due to the high particle concentration suppressing turbulence.

“However, by triggering rapid sedimentation we were able to create structures which are commonly associated with very dilute currents, in which turbulence plays a large role.

“With our colleagues from Roma Tre we examined a similar structure in the field and concluded that it too had been formed by rapid sedimentation from a dense PDC. We think that there may need to be a re-evaluation in some cases of how certain PDC deposits formed, and that an important mechanism may have been overlooked.

“This is important because PDCs are a major hazard, and hazard maps and risk assessments are largely based on interpreting field deposits. As different types of PDC behave differently it’s critical to get our interpretations of their deposits correct.”

The work forms part of Greg’s PhD research, funded by the University of Hull via the Catastrophic Flows Research Cluster, in collaboration with colleagues at the University of the West of England, Hull’s Energy & Environment Institute, and Università degli Studi Roma Tre.

You can read the full paper on Nature Communications here.

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