Since 2009, we have continuously recorded the temperature of Te Wai ā-moe. Over this time, the temperature has often cycled between ~ 15 and 45°C over a period of about 12 months. However, in September 2018 we recorded a departure from this, and for the following 6 months the lake temperature remained elevated (at ~ 30°C). Over the last two weeks, the lake temperature has risen further, at a rate of around 0.5°C per day, to 42°C on April 9. To put this in context, only 1 per cent of post-2009 temperatures have exceeded 42°C and a similar temperature last occurred in May 2016.

The level of volcanic tremor typically also increases when the lake temperature rises, and this has been the case in the last 2 weeks. The current tremor intensity is moderate. In previous heating cycles, this increased tremor lasted for a few days to several weeks.

In the past, eruptions at Ruapehu have occurred more often when the lake exceeded 45°C. However, a temperature of 46°C was recorded in 2016 with no eruption.

Volcanic Alert Level 1 corresponds to minor unrest. While this is the case, it is a useful reminder that eruptions can occur with little or no warning. GNS Science continues to closely monitor Mt Ruapehu and our other active volcanoes.

Agnes Mazot

Duty Volcanologist

Media Contact: Brad Scott (07 374 8211)