Mt Ruapehu: Heightened unrest continues as temperature rises

Monday, 2 May 2022

(Pictured) Te Wai ā-moe the crater lake of Mt Ruapehu from the mountain's summit.

Mt Ruapehu is continuing to show signs of unrest as crater lake temperatures rise to 38C.

Recent airborne gas measurements indicated the volcano had maintained high levels of volcanic gas emissions and strong volcanic tremors.

The Volcanic Alert Level of Mt Ruapehu remains at 2 and The Aviation Colour Code at Yellow.

Eruptions are much more likely at Volcanic Alert Level 2 in comparison with Volcanic Alert Level 1.

* All eyes on rumbling Ruapehu as volcanic activity continues

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

Duty Volcanologist Geoff Kilgour said the current level was consistent with their interpretation of the elevated volcanic unrest.

“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,” Kilgour 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 Alert Level reflects the current level of elevated volcanic unrest. The Volcanic Alert Level should not be used to forecast future activity.”

For six weeks, Mt Ruapehu has demonstrated its strongest volcanic tremors in the past two decades alongside rises in temperatures of Te Wai ā-moe, the crater lake.

In the past week, volcanic tremors have varied with some being stronger than others “with bursts of strong tremor interspersed by short, periods of weaker tremor”.

This represented a change in character in the tremor Kilgour said, and the reasons behind this remain unclear.

“The last three days has seen Crater Lake temperature rise to 38C following a four-week period at 36-37C. Our modelling suggests that to maintain the lake temperature and subtle rise requires ~200-300 MW.

“Due to the heightened volcanic unrest, GNS Science staff are carrying out more frequent aerial gas measurements and Crater Lake sampling.

“A gas measurement flight on 28 April recorded the sixth-highest sulphur dioxide (SO2) flux of 390 tonnes per day since 2003. Sulphur dioxide is a strong indicator gas and is derived from a relatively shallow magma body, which is perceived to currently exist a few kilometres beneath Crater Lake. Further, gas flights will be conducted when weather conditions are suitable,” said Kilgour.

Sampling of Te Wai ā-moe, the Crater Lake was also conducted last week during which scientists observed upwelling of Central Vent and reduced upwelling at the Northern vents area.

They were still awaiting laboratory analysis of the latest Crater Lake fluid and gas samples which would reveal if magma was interacting with the hydrothermal system beneath the lake.

“The high sulphur dioxide (SO2) flux, sustained carbon dioxide (CO2) and continuing strong volcanic tremor, continue to indicate that molten rock (magma) is driving this period of heightened unrest. Increasing Crater Lake temperature is reflecting the increasing upwelling of hot fluids and gases through Central Vent as well as the Northern vents.

“Within the next four weeks, the most likely outcome of this unrest episode is no eruption, or a minor eruption that is confined to the lake basin. Small eruptions are still able to generate lahars, especially in the Whangaehu River.

“The next most likely scenario is an eruption that impacts the summit plateau and generates lahars in multiple catchments, similar to what was seen after the September 2007 eruption or older events like those in 1975 and 1969.

“The chance of a prolonged eruptive episode or a larger eruption, such as occurred in 1995-96 with wider ashfall impacts, 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,” Kilgour said.

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

GNS Science and its National Geohazards Monitoring Centre will continue to monitor Mt Ruapehu closely for further changes.