Vulcanologists trying to predict Tongariro's next move have been driving up and down State Highway 46 collecting samples of gas coming from its crater.
According to GNS vulcanologist Gill Jolly, it has been a difficult task over the last few weeks because of northerly winds and cloudy conditions.
But scientists are still trying to forecast Tongariro and Ruapehu's behaviour through an intensive testing regime, since Tongariro 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," Ms Jolly said.
"There's still gas coming out, but not in the really high concentrations."
Another way of testing the gas was to fly around the crater, but regardless of the tests, it was hard to gauge as the November eruption came with no warning.
However, she said GNS was not seeing any signs the activity from the volcano would become more vigorous.
Meanwhile, scientists await final results of a comprehensive test of Ruapehu's 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 last month.
Ms Jolly said the test taken on Ruapehu last week, which would give them more insight to what is going on in the crater, was 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 Ms Jolly.
They usually happen once a month, but they're doing them more frequently, around every couple of weeks."
She said the exercise of getting a helicopter up to the crater and going through the data was an expensive and time-consuming one.
- © Fairfax NZ News
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