First volcanic alert level rise for Taupō after hundreds of quakes under lake

Tuesday, 20 September 2022

An increase in earthquakes and ground movement at Taupō indicates volcanic unrest, say GNS Science volcanologists who have raised the alert level. Photo/File

Taupō’s volcanic alert level has been raised from 0 to 1 after more than 700 tremors under or around the lake since January.

About 40 quakes a week have been detected around the super-volcano since May, an expert says, and they’re forming two clusters in the central part of the lake.

A Volcanic Alert Level (VAL) of 1 means “minor volcanic unrest” and is causing ongoing earthquakes and ground deformation at Taupō volcano, both under the lake and on land surrounding it.

“Although this is the first time we have raised the VAL to 1, this is not the first volcanic unrest at Taupō,” said duty volcanologist Steven Sherburn.

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“There has been an increase in earthquakes and deformation (ground movement) at Taupō since May 2022 indicating volcanic unrest is occurring.”

There have been 17 previous episodes of unrest over the past 150 years.

“Several of these were more severe than what we are currently observing at Taupō.”

He said the last eruption at Taupō volcano was around 232AD and the chance of an eruption at Taupō remains “very low in any one year”.

“The earthquakes and deformation could continue for the coming weeks or months.

Taupō volcano seismic activity recorded since January. There are almost 700 earthquakes shown within the dashed area of the map.

“While some of the earthquakes may be felt in areas around Lake Taupō, the deformation is currently only detectable by our sensitive monitoring instruments.”

Sherburn said GNS had located almost 700 earthquakes, mainly at a depth of between 4 and 13km beneath the lake, the largest being a magnitude 4.2 event at 6.36am on Saturday, September 10 at a depth of about 5km and was reported felt by 1242 people.

Scientists have been detecting about 40 quakes a week in the region since May.

The next two largest earthquakes this year were both magnitude 3.6 – recorded on May 17 and July 11.

Since 2000, GNS Science has located seven earthquakes larger than magnitude 4 under the lake, the largest was a magnitude 5 on September 4, 2019 near Motutaiko Island.

“The earthquake locations in this year’s sequence are forming two clusters in the central part of the lake.

“There is a cluster beneath the central and eastern part of the lake and a smaller, western cluster centred just offshore from Karangahape.”

In addition to seismic activity, GeoNet monitors ground deformation around Lake Taupō and has observed uplift at a rate of between 20 to 60mm since May at a site at Horomatangi Reef in the lake.

“We interpret the ground uplift and earthquake activity to be caused by the movement of magma and the hydrothermal fluids inside the volcano.”

Sherburn said episodes of unrest were common at calderas around the world and could continue for months or years and not result in an eruption.

“If there was increased unrest, then we would see more substantial impacts on the local area.

“These could include earthquakes with ground shaking and potentially landslides on steep cliffs, especially after rain.”

He said liquefaction could occur in the event of larger earthquakes.

“The Volcanic Alert Level reflects the current level of volcanic unrest or activity and is not a forecast of future activity.

“While Volcanic Alert Level 1 is mostly associated with environmental hazards, potential for eruption hazards also exists.”