Mt Ruapehu: Crater Lake is now cooling again

Published: Mon May 4 2020 2:30 PM

Volcanic Alert BulletinRUA – 2020/05
Mon May 4 2020 2:30 PM; Ruapehu Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains at Green

An expected cooling trend for Crater Lake (Te Wai ā-moe) is now confirmed. The lake reached a peak temperature of 42°C in early April, and is currently at 35°C.

During February-April, Crater Lake (Te Wai ā-moe) heated slowly to a peak temperature of 42ºC. As often happens in a heating-cooling cycle, there is a period of slow change before a cooling trend is clearly shown in the data. That trend is now confirmed with current temperatures close to 35ºC, with further slow cooling expected.

Today the volcanic tremor intensity is weak, as it has been during the past month. After a peak of moderate strength in early March, the tremor declined slowly, almost in parallel to the lake’s cooling trend. Our energy input modelling points to a low-level but continued flow of heat into the lake, which indicates that the underlying vent area is open to upflows of volcanic gases and hydrothermal fluids

Last week GNS volcanologists briefly visited the lake to service the monitoring equipment there. They reported the lake as a uniform grey colour with just a few surface slicks and no obvious upwelling. At that time the water level had dropped to about 30 cm below overflow but following this weekend’s rain the lake is again overflowing into the upper Whangaehu River.

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.

Michael Rosenberg

Duty Volcanologist

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