Mt Ruapehu: Crater Lake heated to 40°C

Published: Wed Mar 18 2020 11:55 AM

Volcanic Alert BulletinRUA – 2020/04
Wed Mar 18 2020 10:30 AM; Ruapehu Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains at Green

Crater Lake (Te Wai ā-moe) has been heating in response to an input of hot gases and hydrothermal fluids following volcanic earthquakes beneath Mt Ruapehu in February. The lake temperature is now 40°C. GNS Science volcanologists have collected further data to understand current activity.

Volcanologists have collected water samples from Crater Lake this week to understand current activity at the volcano. These samples are being analysed this week, with chemistry results expected by next week.

Crater Lake (Te Wai ā-moe) has heated from 24ºC to reach about 40 ºC following these volcanic earthquakes. We reported in our last bulletin that upwelling of grey sediment and sulphur slicks on the lake surface were observed. Now the lake is well mixed and has changed to a uniform grey colour. The continued flow of gases and hydrothermal fluids through the lake show that the volcano’s vent underlying Crater Lake is open.

The lake is overflowing at the outlet channel, with a notable decrease in the flow rate between our last two visits.

Volcanic tremor increased in response to the volcanic earthquakes, peaking in early March, then declined slowly until today.

Modelling of the energy input into the lake shows that the heat input increased from around 200 MW to around 600 MW but has now declined as the temperature rise has slowed. Heating cycles such as this are very common at Ruapehu.

The amounts of carbon dioxide (CO2) and sulphur gases (SO2 and H2S) in the atmosphere above the volcano measured on 28 February was greater than when measured on 7 February. However, the recent values are not unusual and are within the ranges measured over the past year.

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, acoustic and thermal sensors, GPS receivers, visits to the lake area and gas flights.

Art Jolly Duty Volcanologist

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