Mt Ruapehu: Activity and Crater Lake temperature update. Volcanic Alert Level remains at Level 1.

Published: Tue Aug 11 2020 9:30 AM

Volcanic Alert BulletinRUA – 2020/07
Tue Aug 11 2020 9:30 AM; Ruapehu Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains at Green

New observations in July-August continue to indicate low levels of volcanic activity at Ruapehu. The Volcanic Alert Level remains at 1. Crater Lake (Te Wai ā-moe) has cooled from a peak temperature of 42°C in early April and is currently around 22-23°C. Recent monitoring results indicate continuous gas flux into the lake.

Crater Lake (Te Wai ā-moe) has a long history of heating and cooling, with each cycle occurring over a few months. Since April this year, lake temperature has decreased from a high of 42°C to around 22-23 °C. This lower lake temperature is normal for Crater Lake.

To keep the lake at this temperature, low-level heat must continue to flow into the lake. This indicates that the underlying vent area is open to volcanic gases and hydrothermal fluids. Other signs that point to this open vent are visible upwellings and sulphur slicks on the lake surface.

Over the last three months, we have conducted two gas flights and collected two lake samples for laboratory analysis. The results from these visits show an increase in H2S (hydrogen sulfide) gas and declines in CO2 (carbon dioxide) and SO2 gas (sulphur dioxide). This is consistent with more hydrothermal than magmatic chemical reactions in the lake.

The level of volcanic tremor intensity has been variable but weak, over the past three months. Small earthquakes continue to be located near the volcano.

None of these observations are unusual for Mt Ruapehu. All observations over the past months indicate that the volcano remains in minor volcanic unrest and at Volcanic Alert Level 1.

Some people may have noticed that our camera on the north side of the volcano has been shifted. This is part of the ongoing refinement of the GeoNet networks and equipment used to monitor the active volcanoes.

The Volcanic Alert Level remains at Level 1. The Volcanic Alert Level reflects the current level of volcanic activity and is not a forecast of future activity. Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of volcanic unrest. There is no change in the Aviation Colour Code and it remains at Green.

GNS Science and the National Geohazards Monitoring Centre continues to closely monitor Mt Ruapehu for further signs of activity. GeoNet monitors Mt Ruapehu via network of seismic and acoustic sensors, GPS receivers, sensors in the lake and visits to the lake area, and gas flights.

Yannik Behr Duty Volcanologist

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