Volcanic tremor strength at Mt Ruapehu has declined to weak levels over the past week.

Crater Lake (Te Wai ā-moe) temperature is currently 28 °C and has continued its slow cooling trend over the past 3 to 4 weeks. Heat flow calculations indicate that heat entering the lake is around 100-160 MW, down from 300-400 MW last month. The lake level has also responded to the heavy rainfall over the past week, with an increase in overflow.

Although weather conditions have not allowed gas measurement flights in the last few weeks, the last relatively high sulphur dioxide (SO2) and carbon dioxide (CO2) measurements are consistent with a continued period of moderate volcanic unrest at Mt Ruapehu.

The level of unrest is now considered moderate rather than heightened, however the potential for eruptive activity remains.

Scenarios

Within the next three weeks, the most likely outcomes of the ongoing unrest are either minor eruptive activity that is confined to the lake basin, or no eruption. Minor eruptions may generate lahars (dangerous volcanic mudflows) in the Whangaehu River.

The next likely scenario is a larger eruption that impacts the summit plateau with volcanic surges. That event could generate lahars in multiple catchments, like what was seen after the September 2007 eruption, or like those in June 1969. An eruption of this size would cause life-threatening hazards on the summit plateau and in valleys impacted by lahars.

The chance of a prolonged eruptive episode or a larger eruption, with wider ashfall impacts such as occurred in 1995-96, is higher than it was before the start of elevated unrest in March 2022, but within the next three weeks remains very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions.

Summary

The level of volcanic unrest has declined from heightened to moderate at Mt Ruapehu. GNS Science staff are carrying out more frequent aerial observations and gas measurements when weather conditions are suitable.

Our interpretation of the observational data and activity is consistent with moderate volcanic unrest and therefore the Volcanic Alert Level remains at Level 2. The Aviation Colour Code remains at Yellow.

Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of moderate volcanic unrest.

The Volcanic Alert Level reflects the current level of moderately elevated volcanic unrest. The Volcanic Alert Level should not be used to forecast future activity. However, at Volcanic Alert Level 2, eruptions are usually more likely to occur than when a volcano is at Volcanic Alert Level 1.

Volcanic Alert Level 2 indicates the primary hazards are those expected during volcanic unrest; steam discharge, volcanic gas, earthquakes, landslides, and hydrothermal activity. While Volcanic Alert Level 2 is mostly associated with volcanic unrest hazards, eruptions can still occur with little or no warning. Volcanic Alert Levels 3, 4 and 5 are reserved for eruptions with varying impact distances.

For information on access to the Mt Ruapehu area, please visit the Department of Conservation’s websites on volcanic risk in Tongariro National Park 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 https://getready.govt.nz/emergency/volcanic-activity/.

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

Craig Miller

Duty Volcanologist

Media Contact: 021 574 541 or media@gns.cri.nz