Since 15 March (NZ local time) GNS Science volcanologists have detected an ongoing sequence of seismic events beneath Mt Ruapehu that can be categorised as volcanic earthquakes. They have relatively small magnitudes and cannot be located by GeoNet’s automatic earthquake detection system but the pattern of seismic recordings indicates a source beneath the summit area. The distinction between volcanic earthquakes and volcanic tremor is gradational and a sequence of discrete volcanic earthquakes can evolve into a more continuous seismic signal which would then be called volcanic tremor. The crater lake (Te Wai ā-moe) temperature is currently at 39 oC, which is above the 95th percentile of the long-term distribution of measured temperatures at the lake (i.e. only 5% of temperature measurements made since 2009 are equal or greater than 39 oC). It has been at an elevated temperature since August 2017 (see also RUA -2017/01).

It is not unusual to observe volcanic earthquakes during phases of increased heat input into the lake. Similar episodes were observed during April 2016 and September 2017 but did not result in an increase in volcanic unrest. The Volcanic Alert Level, therefore, remains at 1 and the Aviation Colour Code at Green.

GNS Science continues to closely monitor Mt Ruapehu and our other active volcanoes through the GeoNet project.

Yannik Behr Duty Volcanologist

Media Contact: Brad Scott