How to survive a volcanic eruption

MICHAEL DALY
Last updated 17:37 10/04/2014

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University of Canterbury geologists are planning to test the theory that the best way to avoid flying volcanic rocks is to face an eruption, rather than run from it.

In an experiment that sounds like something out of the fun science television programme, MythBusters, they are going to be doing the testing with a large catapult called a trebuchet that can fling rocks up to 100 metres. It can be seen in action here.

They have also built a pneumatic cannon that will be used to find how much shrapnel is produced when rocks hit different ground surfaces.

Another use for the cannon is to fire volcanic rocks at different types of roofs to find out which stand up best to the assault.

Part of the research will investigate what happens when something semiliquid like magma flies through the air. An early stand-in used to try to mimic magma was made from playdough wrapped in condoms.

The trebuchet and cannon experiments tie in with work being done to understand the August 2012 Tongariro eruption, the first time Tongariro erupted in more than a century.

Researchers from Canterbury's geology department, working with government agencies, have calculated that had anyone been on one section of the Tongariro Crossing hiking trail during the eruption, they would have had a 16 per cent risk of being killed.

Fortunately, the eruption happened at night when no-one was on the track. Nor was anyone staying in the Ketetahi Hut, which took direct hits and was significantly damaged.

Postgraduate student Rebecca Fitzgerald said it was thought 13,000 to 16,000 pieces of rock were thrown out of vents during the eruption.

They travelled up to 2.3 kilometres, left craters ranging in diameter from 30 centimetres to 10.8m, and were probably travelling about 200m per second when they left the vents.

"So even the smallest blocks probably would have killed you," Fitzgerald said.

About 2.6km of the Tongariro Crossing, which about 80,000 people walked each year, was in the area where the rocks landed.

Researchers had looked at what would have happened in a bigger eruption, where the amount and velocity of blocks was increased.

"Anyone who was near Ketetahi Hut in that eruption scenario would be killed. There was a 100 per cent chance of fatality in about a 200m long area," Fitzgerald said.

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University of Canterbury senior lecturer in physical vulcanology Dr Ben Kennedy said the trebuchet built at the university should help understand the impacts of volcanic hazards, allowing risk during a volcanic eruption to be better managed.

"It was quite scary to see the damage these flying rocks had done to sections of the Tongariro Crossing hiking trail and the holes ripped through the Ketetahi Hut," he said.

Research was at an early stage with the cannon and trebuchet, working out which scenarios they were good for reproducing. Some early tests this week had been filmed by a Discovery Channel team who were in the country.

In a year or so it could be time to think about testing whether it was possible to dodge a volcanic bomb, Kennedy said.

"There are people who have been in eruptions and they've said they could look up at bombs falling and work out whether they were coming their way or not."

The research could also look at whether it was more effective to huddle behind a rock.

"You could put a sign up on the Tongariro Crossing and say, 'if there's an eruption, do this'," Kennedy said.

 "At the moment those signs don't exist."

- Stuff

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