Taupō 'supervolcano' just had its shakiest year in decades

Grey circles show locations of earthquake swarms at Taupo last year, while blue triangles show the GeoNet seismic network and red ones show the Eclipse programme's own network. Image / Supplied

Scientists are taking a deeper look at a series of recent quakes at New Zealand's best-known "supervolcano" that proved to be the area's largest in decades.

But they assure people that Taupō is no closer to blowing.

The huge, hidden caldera volcano at the centre of the North Island has been known to cause some of the largest eruptions in the planet's history.

Lake Taupō essentially fills the hole left by one of those monster blows - the Oruanui eruption, around 25,400 years ago, which spewed more than 1100 cubic km of pumice and ash into the atmosphere that travelled as far as Antarctica.

Taupō's most recent major episode - a devastating event 1800 years ago - fired out more than 120 cubic km of pumice and ash and obliterated the surrounding landscape.

The volcano has remained quiet for centuries, yet around each decade, scientists observe a bout of heightened seismic activity – and last year's deep rumbles proved a stand-out compared with recent times.

Throughout 2019, GeoNet reported more than 1100 earthquakes in the region, particularly beneath the area of the volcano covered by the lake - far more than the yearly average of several hundred earthquakes.

While most of these were small, one quake recorded on September 4, and centred in the middle of the lake near Motutaiko Island, registered a magnitude of 5.0.

That was enough to cause shaking from Turangi to Taupō, knocking items off shelves and causing highway slips, and was swiftly followed by another quake, measuring 4.5.

"A magnitude 5 earthquake may seem small when compared to other parts of New Zealand, but this is the largest earthquake to occur in the vicinity of Taupō volcano for several decades," said Dr Finn Illsley-Kemp, a volcano seismologist at Victoria University.

The reason why these quakes happened was now being investigated by scientists working under the five-year, $8.2m MBIE-funded ECLIPSE project, run through Victoria University of Wellington, in collaboration with GNS Science and Massey University.

Illsley-Kemp couldn't yet say what precisely had triggered the earthquakes – but added that the answer was likely to be complex.

"Taupō is an active volcano but it is also crossed by many crustal faults belonging to the Taupō rift," he said.

"Untangling the interaction between the volcano and the rift is very challenging and a key research aim, so watch this space."

Many people in the area who experienced September's shaking were naturally interested in the team's work, he said, but they'd found no reason to believe the volcano was on a path to eruption.

The September 4 quake, measuring 5.0, struck in the heart of Lake Taupo. Photo / GeoNet

"The earthquakes died down very quickly after the September earthquakes and it now looks as if Taupō is back to its background business-as-usual," he said.

"The 2019 earthquake activity shows that Taupō is an active area and close monitoring by GeoNet is very important."

The volcano's last comparable episodes played out in 2008, and, before that, between 1997 and 1998.

"We don't yet have a clear picture of what may be causing these episodes of seismicity. Such activity is a normal part of the life of this active volcano, and of ours living on and around it.

"In the vast majority of these periods the volcano quietens back down. Very occasionally they are leading to something more eruptive.

"Our ECLIPSE research programme aims to reduce uncertainty around the point at which that change might happen. We're partnered with emergency managers and iwi to support plans for dealing with unrest episodes, and also for the very unlikely case of an eruption."

In the wake of the recent quakes, the scientists were setting up a new network of 13 temporary seismometers around the lake.

"This will significantly improve the seismometer coverage around Taupō and will help our understanding of the volcano in two ways," he said.

"Firstly we will be able to study the earthquakes in more detail by detecting many smaller earthquakes and calculating their location with far higher accuracy. This will help us to determine whether future earthquakes are being driven by the volcano or not."

"Secondly, it would allow them to directly image the roots of the volcano beneath the lake, revealing more about the size and location of the magmatic system."

"It will enable us to interpret earthquake activity, such as the 2019 swarms, in the context of the magma system's location."

Scientists are taking a deeper look at a series of recent quakes at New Zealand's best-known "supervolcano" - Taupo - that proved to be the area's largest in decades. Photo / Peter Wilton

The work was being carried out in close collaboration with local iwi, particularly Ngāti Tūwharetoa, the kaitiaki of Taupō-nui-a-Tia.

"An important aspect of this work has been consultation with land trusts and hapū to make sure that the local community is aware of and approves of our research," Illsley-Kemp said.

"We've achieved this through a diverse team, including iwi researchers, and a kanohi ki te kanohi approach involving many hui and wānanga.

"Ngāti Tūwharetoa have been interested and supportive and we hope that the strong collaboration will continue beyond the lifespan of the seismometer network.

"This co-production ethos is a core component of the ECLIPSE project and as well as with Ngāti Tūwharetoa we are working closely with trusts from Ngāti Rereahu, Ngāti Awa, and Te Arawa."

One of ECLIPSE's iwi research leaders, Kelvin Tapuke, said mana whenua had an intimate knowledge of their rohe, which had been passed down over many centuries.

"Mana Whenua are the kaitiaki of their areas. They have the right to access tools to inform them of the rights and responsibilities expected in those Kaitiaki roles," he said.

"Iwi are keen to engage with both Mātauranga Māori and Western Science knowledge."

"The same volcanic data in Mātauranga Māori has been coded in pitopito kōrero, pūrākau, waiata, haka. Mātauranga Māori is a key aspect of our research as we explore oral histories of volcanic unrest and eruptions."

"Being informed by both Mātauranga Māori and Seismometers helps equip Iwi with the knowledge to make good decisions"