Mt Ruapehu: Activity and Crater Lake temperature update

Published: Tue May 26 2020 9:00 AM

Volcanic Alert BulletinRUA – 2020/06
Tue May 26 2020 9:00 AM; Ruapehu Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains at Green

After a recent heating cycle, we anticipated that Crater Lake (Te Wai ā-moe) would begin cooling to lower temperatures seen earlier this year. The lake reached a peak temperature of 42°C in early April and cooled to around 35°C shortly after. Recent monitoring indicates continuous gas flux which has kept the temperature around 35°C through May.

Activity at Crater Lake (Te Wai ā-moe) is often dominated by a heating-cooling cycle. These cycles last weeks-to-months. After peaking in April at 42°C, the lake cooled to 35°C by early May and has remained around that temperature all month. The further slow cooling that we expected at the beginning of May has not happened.

GNS Science volcanologists have continued to monitor Mt Ruapehu, and as lockdown restrictions have allowed we have visited the lake to collect water and gas samples and make a gas flight. We detected an increase in CO2 gas (carbon dioxide) input while SO2 gas (sulphur dioxide) remains steady. This is consistent with our energy input modelling which points to a low-level, but continued flow of heat into the lake.

It further indicates that the underlying vent area is open to upflows of volcanic gases and hydrothermal fluids, and so is currently preventing the lake from cooling further. Other signs that point to an open vent status are visible upwellings and sulphur slicks on the lake surface. None of these observations are unusual for Mt Ruapehu.

The level of volcanic tremor intensity remains variable but weak, as it has been during the past month.

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 from 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 a 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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