Mt Tongariro: looming threat

There have been no reports of further activity at Mount Tongariro overnight as scientists, like everyone else, wait to see what the volcano does next – and it could be a long wait with the next burst of activity coming with little or no warning.

Volcanologists are today awaiting results of the analysis of ash samples from Monday night’s eruption taken to Massey University for analysis.

Ash covers a track after Mount Tongariro erupted on Monday night.

Mount Tongariro erupted at 11.50pm on Monday sending ash and rocks up to 1km into the air.

Scientists are now looking for clues to the origin of the eruption, thought to be a steam eruption, caused by rising magma heating groundwater to the extent the steam pressure blows out.

Vulcanologist Steve Sherburn says by putting the ash under the microscope they hope to tell if there was any magma involved.

Tongariro’s first eruption in a century came after a sporadic increase in earthquakes, but the eruption itself was unexpected. The mountain’s seismic drum showed no earthquakes leading up to the eruption.

“The earthquake activity was sporadic,” says Steve.

“The text book example of what we experienced Monday night would be that we would have some trend in activity. But it had a bit of activity and quiet, a bit of activity, quiet. And it’s been relatively quiet the last few days, and then, bang.

“That’s what made it very difficult. I guess we are fortunate we reacted to the earthquakes over the past few weeks by raising the alert level, so at least people were aware of this and it didn’t come straight out of the blue.”

Volcanoes are individuals, each with their own patterns of activity, says Steve.

The difficulty Tongariro presents for scientists is that it hasn’t erupted for 100 years.

“We don’t know what happened before it started erupting last time,’ says Steve.

“If you have a volcano that erupts quite frequently quite often you can see a pattern. When you can recognise a pattern, see what’s causing the pattern, then you are in a much better situation.

“It’s very difficult to have a pattern if it hasn’t erupted for a 100 plus years.”

This image shows seismic activity during the last 24 hours at a station at the Tongariro Volcano.

Steve says Tongariro is similar to Mount Kirishima in southern Japan.

“The Tongariro complex is a structured volcano with different eruptions having created different land forms,” says Steve.

“Kirishima is very similar and hadn’t erupted for some time as well.”

Kirishima’s Shinmoedake crater burst into action in January 2011 and continued for about six months.

“We could potentially be looking at a Kirishima kind of thing. It’s the 64 million dollar question to which we don’t have any answers at the moment.

“What we are hoping is if this is going to develop into a larger magmatic type eruption we will see some kind of signals preceding that, and we can interpret this in terms of seismic ground deformation, volcanic gases we can sample.

“There’s a range of things, some dependent on weather. Of course we are not going up there until we know what’s going on.”