Mt Ruapehu tests due back soon

22:06, Dec 05 2012
Mt Ruapehu crater lake - file shot 2003
BACK THEN: The Mt Ruapehu crater lake in 2003.

Uncertainty shrouds Mt Ruapehu’s activity as scientists await final results of a comprehensive test of its crater lake due this week.

The volcano has thrown up stable results over the last fortnight, but scientists are still on high alert after Tongariro’s unexpected eruption in November.

Since Tongariro’s eruption on August 6, which happened after more than a century of dormancy, both volcanoes have been put through a more intensive testing regime.

GNS vulcanologist Gill Jolly said the test taken on Mt Ruapehu last week, which would give them more insight to what is going on in the crater, is due any day now.

“We’re still looking at the temperature of the crater lake and that’s pretty stable,” she said.

“The seismicity has been pretty low for the last wee while, so it’s relatively quiet but we still have that uncertainty about what’s happening underneath the vent. So we’re still on a high level of alert.”


The test involved flying a helicopter to the crater lake, taking a water sample, and analysing the gases that have dissolved in it.

“Those gases can tell us about what’s happening in the vent area around 600m down,” said Jolly.

“They usually happen once a month, but they’re doing them more frequently, around every couple of weeks.

"They do need to go up there and collect a sample – so it’s quite expensive and time consuming."

Vulcanologists are also trying to forecast Mt Tongariro’s behaviour, which last blew on November 21.

“The gases were relatively low - similar to some of the measurements we’ve done over the last couple of months, which were not as high as immediately after the eruption on August 6,” she said.

“There’s still gas coming out, but not in the really high concentrations.”

One of the ways the scientists test Mt Tongariro is by driving along State Highway 46, collecting samples of the gas above the car – a task made difficult by northerly winds and cloudy conditions.

Jolly said these test can be used as a forecasting tool, but it is difficult to read the future because the November eruption came with no warning.

However, she said GNS is not seeing any signs the activity from the volcano would become more vigorous.

Fairfax Media