Ruapehu Crater Lake sampled, variable gas emissions and low volcanic tremor levels continue. The Volcanic Alert Level remains at Level 2.

Published: Tue Jun 28 2022 12:30 PM

Volcanic Activity BulletinRUA – 2022/17
Tue Jun 28 2022 12:30 PM; Ruapehu Volcano
Volcanic Alert Level remains at 2
Aviation Colour Code remains at Yellow

Despite intermittent gas pulses, volcanic gas emissions have declined. Volcanic tremor remains low, while the Crater Lake temperature has recovered slightly to 25 °C. The Volcanic Alert Level remains at Level 2.

Over the last week, volcanic tremor has remained weak at Mt. Ruapehu. It has been 10 days since the last notable tremor, and almost a month since the period of strong tremor that commenced in mid-March 2022. Crater Lake (Te Wai ā-moe) temperature decreased from a high of 40 °C in early-May to 21 °C on June 14, and in the last two weeks has recovered to 25 °C. This is consistent with heat flow into the lake of 250-300 MW.

On 23 June, fine weather allowed for Crater Lake sampling and a gas emission flight. The gas emission rates through Crater Lake were approximately 10% of those measured in the previous flight on 13 May. However, on 24 and 25 June, recently installed, automated sulphur dioxide (SO2) gas measuring equipment at Ruapehu measured gas emission rates similar to those observed by the gas flight on 13 May. The range of the gas output over just three days is considered to reflect short-term natural variability of gas emissions at the volcano.

The end of the period of strong volcanic tremor, from mid-March to early-June, indicates that active magma intrusion has slowed or stopped. This interpretation is supported by generally lower gas emission rates. However, gas emissions are also quite variable indicating small, short-lived pulses of gas are still reaching the surface. When taken together with the slight recovery of Crater Lake temperature, the observations remain consistent with a continued period of moderate volcanic unrest at Mt Ruapehu.

The potential for eruptive activity remains. Over the last 2-3 months a magmatic intrusion has occurred under the volcano, which increased the likelihood of eruptive activity above the typical level. The likelihood of eruptive activity has decreased from that during the period of strong tremor, but has not returned to typical long-term levels.

Within the next two weeks, the most likely outcome of the ongoing unrest is no eruption. Minor eruptive activity, confined to the lake basin, is also possible, which could generate lahars (volcanic mudflows) in the Whangaehu River.

The next most likely scenario is an 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. 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 two weeks, this scenario remains very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions.

Despite low levels of volcanic tremor, the observation of small, short-lived pulses of gas and a slight recovery of the Crater Lake temperature remain consistent with a continued period of moderate volcanic unrest at Mt Ruapehu 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 moderate to heightened 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 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.

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

Steven Sherburn, Duty Volcanologist

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