Mt Ruapehu unrest: Chances of eruption are higher but it remains 'very unlikely' - expert

Tuesday, 26 April 2022

Mount Ruapehu's crater lake Te Wai a Moe is sitting at 37 degrees – and that requires “a substatial amount of heat”.

The crater lake’s still hot and the tremors continue, but experts say an eruption at Mt Ruapehu is still unlikely.

However, the chances are higher than they were two months ago.

GNS has been monitoring the heightened unrest of the volcano for the past five weeks as it has exhibited sustained volcanic tremors.

But recent analysis of water samples from the lake don’t show the kind of changes that hint at magma mixing with water under the surface, experts say.

* Why Mt Ruapehu is restless: Four weeks of strong volcanic tremor and a warm crater lake

* Slow Ruapehu temperature rise hints at risky pressure build up at volcano

The volcanic alert level for Mt Ruapehu remains at level 2. The mountain is pictured from the start of the Tongariro Alpine Crossing.

* What do the volcanic conditions at Mt Ruapehu suggest?

“The chances of a prolonged eruptive episode or a larger eruption…is higher than it was two months ago, but remains very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions,” said duty volcanologist Steven Sherburn.

There have been “strong volcanic tremor signals” – the combined longest-strongest recorded over the past 20 years, volcanic unrest, and more gas being emitted, which Sherburn said hinted at magma interacting with the geothermal system within the volcano.

“The Crater Lake (Te Wai ā-moe) temperature has remained around 37 °C (range 36-38 °C) over the past three weeks. While the temperature has not increased, our modelling requires that a substantial amount of heat (about 200-300 MW) is still needed to sustain this high lake temperature.”

However, a statement on GeoNet said there were no indications to suggest any changes reflected in the crater lake conditions.

“We did not observe an increase in magnesium concentration [in water samples] that would have pointed at some potential magma-water interaction below the surface. We will keep sampling the crater lake regularly to monitor any changes in the water chemistry.

“The static lake temperature and lack of chemical response indicate processes at shallow depth below the Crater Lake are not being reflected in the lake conditions.

“Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of elevated volcanic unrest,” Sherburn said.

The volcanic alert level for Mt Ruapehu remains at level 2 and the Aviation Colour Code is at Yellow with temperatures of Te Wai-ā-moe (The Crater Lake) sitting at a stable 37 (degrees), a statement said.

Volcanic Alert Level 2 indicates the primary hazards are those expected during volcanic unrest; steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity.

The volcanic tremors have been exhibited as elevated gas output and heat flow into the summit crater lake while the tremor levels have also fluctuated over the past seven days but continue to be elevated overall.

It’s most likely this unrest won’t lead to an eruption, but GNS Science and its National Geohazards Monitoring Centre will keep looking out for any changes.

For information on access to the Mt Ruapehu area, visit the Department of Conservation’s websites on volcanic risk in Tongariro National Park and follow the DOC Tongariro Facebook page for further updates.

For information about responding to volcanic activity, there are guidelines from the National Emergency Management Agency's Get Ready website.