Island of glass

island-of-glass

Deep in the Mediterranean Sea, between Sicily and Tunisia, lies a tiny island complete with secluded coves, hot springs and the occasional celebrity holiday maker. However, despite its modern day idyll, the Italian island of Pantelleria has a violent volcanic past, which scientists are only now beginning to understand.

45,000 years ago a volcanic eruption covered the whole island in a layer of hot molten glass, destroying all life. Plants and animals have since returned but the green glassy deposit still remains, draped over hills and cliff tops.

Recently a team of volcanologists from Leicester University was able to take advantage of this glassy relic of volcanic history to find out more about Pantelleria’s past.  The team, headed by Dr Rebecca Williams and Dr Mike Branney, analysed the chemical composition of the glassy deposit covering the island. The deposit is an example of an ignimbrite, material formed from the hot gases and rock that are spewed out during volcanic eruptions. The research shows that the destructive current that forms ignimbrite is actually much more complex than was previously thought.

The team analysed how levels of Zirconium in the ignimbrite varied with time and distance from the eruption. This meant that they could reconstruct the movements of Pantelleria’s pyroclastic density current, the current of hot gas and rock which laid down the ignimbrite.These currents are a particularly lethal aspect of volcanic eruptions. They can travel at speeds of up to 450 miles per hour and historically have been responsible for half of all volcano-related deaths.

Williams and Branney’s research shows that the Pantelleria ignimbrite was not created by sudden inundation from the pyroclastic density current as was previously thought. Instead the current travelled gradually over the island and even retreated a little as the eruption entered its final stages.  “What we showed is that the current gradually extended out from the volcano, particularly along the valleys at first, and then gradually got to higher and higher points. It went over the topography so that the area of the current increased in time and then, as the eruption waned, the area covered by the current gradually decreased,” said Dr Branney.

These new findings on pyroclastic density currents will help volcanologists better understand the complexities of volcanic eruptions. They may also help oceanographers, as they are very similar to the turbidity currents that transport sediment over the ocean floor. Dr Branney explains: “I think that [turbidity currents] probably move in a very similar way to pyroclastic currents but you can’t do this sort of study because they don’t show the same sorts of chemical variation.” So maybe this better understanding of Pantelleria’s violent volcano will one day also help us understand more about the tranquil Mediterranean Sea that surrounds it.

 

IMAGE: Michael Leithold

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