Mt Ruapehu earthquakes: Summit cluster 'unusual' says GNS Science

Mt Ruapehu. Photo / NZME

A recent cluster of earthquakes beneath the summit of Mt Ruapehu has been described as unusual by volcanologists.

GNS Science Duty Volcanologist Geoff Kilgour said earthquakes regularly occurred in the Tongariro National Park, towards the southern portion around Ruapehu.

However, since December 30, GNS has recorded a sequence of tectonic earthquakes beneath Ruapehu's summit area which, compared with historical records, was unusual.

"While these earthquake clusters are uncommon, none of our monitoring data suggests that the volcano is exhibiting increased levels of activity.

Plot of the location and number of earthquakes beneath the summit area at Ruapehu since 2019, with earthquakes since December 30 2021 highlighted. Photo / GNS

"There has been no observable response from other continuous monitoring data such as Crater Lake temperature, lake level, or volcanic tremor.

"Therefore, our current assessment is that a relatively deep stress release has occurred below the volcano but this has not affected the volcano's hydrothermal system," Kilgour said.

"Our team will be conducting a scheduled gas flight and will sample Ruapehu's Crater Lake in the coming days, weather permitting."

There are two broad types of earthquakes at volcanoes. They are: volcanic earthquakes, which include tremors that are directly related to the movement of fluids, magma and/or the hydrothermal system, and tectonic earthquakes which result from rocks fracturing - movement on small faults.

The Volcanic Alert Level at Mt Ruapehu stays at Level 1 which reflects the current level of volcanic unrest.

The Aviation Colour Code remains at colour green.