Mt Ruapehu crater lake sees quick jump in temperature and moderate tremors

Wednesday, 10 April 2019

A GNS Science technician takes measurements at Mt Ruapehu's Crater Lake. This is part of GeoNet's regular monitoring of the volcano.

Moderate tremor levels have been recorded at the Mt Ruapehu crater lake, and water temperatures have shot up in the past two weeks, but volcanologists say it's nothing out of the ordinary yet.

Te Wai ā-moe, the crater lake, often cycles between 15 degrees C and 45C throughout the year, but temperatures have been unusually consistent over the past six months, stuck at about 30C since September as steam and gas from the geothermic system flow into the lake.

'We haven't really seen that before,' said volcanologist Brad Scott.

But in the last two weeks, things have appeared to return to normal as the lake entered a heating, jumping up by around half a degree per day, and currently sits at 42C.

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Mt Ruapehu's crater late has jumped up half a degree a day in the last two weeks

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That rate of heat is 'par for the course', Scott said.

'When the lake is in a heating episode, that's pretty typical.'

If the lake temperature gets above 45C, it is considered possible that there may be an eruption, though this is no guarantee. In 2016, the lake hit 46C without an eruption.

Scott said there is no way of knowing where the lake will top out.

'We can't predict whether it will keep increasing, but intuitively it normally peaks out in the mid to high 40s, that's probably our highest expectation. There's always the possibility it will carry on to higher temps. But there aren't any factors like the rate or the starting temp we can use to predict how high it will get.'

'The volcano being a volcano, it may peak out at 42 degrees, it may continue rising, there's just no way of knowing.'

Along with the quick heat rise, there have been moderate volcanic tremors recorded - far below what a human could see or feel, but it could be an indicator of surface tension if the tremors increase.

Right now, the volcano remains at Level 1, which is the lowest level an active volcano can be, but volcanologists will keep an eager eye on its actions.

'It's kinda behaving like Mt Ruapehu always has. Business as usual,' said Scott.