Mt Ruapehu: Seismic activity increases after lake temperature peaks.

Published: Mon Oct 31 2016 3:30 PM

Volcanic Alert BulletinRUA – 2016/10
2016-10-31 14:15:00 +1200 +1200; Ruapehu Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains Green

Since early September, Mt Ruapehu’s Crater Lake had been heating at a rate of around 1°C per day, reaching a maximum of 40ºC on October 4. The lake temperature has cooled slightly since then and is now hovering around 37°C. After October 18, the level of volcanic tremor under Mt Ruapehu increased in strength. Volcanic tremor is always present at Mt Ruapehu, however the level can vary.

An increase in the strength of volcanic tremor began on October 18, where a sharp increase was noted before the energy declined a day later. Subsequent tremor increases occurred again on October 25 and 28, and currently remains higher than normal. These tremor pulses do not appear to be related to any variation in the lake temperature. Our records show that similar periods of increased volcanic tremor were present May-June 2016, again when the lake temperature was high. Importantly, no eruptive activity or geysering was noted in Crater Lake during the previous periods of volcanic tremor.

Weather conditions have not been ideal for mountain observations. Nevertheless, our scientists will be visiting the lake to collect water samples for further analysis and making a gas flight when the weather conditions improve.

The active crater at Mt Ruapehu is occupied by Crater Lake and it displays temperatures that typically range between about 15 and 40°C and the phases can last between about 9 and 20 months. The lake cooled to a minimum of 12°C in mid-August and then remained at 13-14°C until early September when it started to heat again and reached a peak of 39.8°C on October 4.

GNS Science volcanologists continue to closely monitor Ruapehu through the GeoNet project. The Volcanic Alert Level for Mt Ruapehu remains at Level 1 (minor volcanic unrest) and the Aviation Colour Code also remains unchanged at Green. The Volcanic Alert Level ranges from 0 to 5 and defines the current status at a volcano. Aviation Colour Codes are based on four colours and are intended for reference only in the international civil aviation community.

Brad Scott (Duty Volcanologist)

Clear but very windy Mt Ruapehu this morning.

Clear but very windy Mt Ruapehu this morning.