After 700 earthquakes, what happens next at Taupō supervolcano?

This map shows some 700 earthquakes recorded this year around Taupō volcano, which now sits at alert level one for the first time. Image / GeoNet

Scientists watching our best-known super-volcano say underground rumbles around an unsettled Taupō could carry on through summer – and aren't ruling out more local shakes.

But it's also possible that the episode - which last month prompted GeoNet to raise the hidden caldera volcano's alert level above zero for the first time ever - has already peaked.

A local sequence that began in May has now generated more than 700 quakes: among them, a 4.2 event and several slightly smaller ones recorded within days of each other in mid-September.

The largest cluster was located around the central and eastern part of the lake, at depths of about 4km to 13km, where scientists have also been observing centimetres of ongoing ground uplift.

It's in this area that scientists recently pin-pointed a hidden magma chamber, thought to sit about 5km below ground.

Earthquakes located by GeoNet in the Lake Taupō area from January 1 to September 18, 2022. Most earthquakes shown here were located between 4 and 13 km deep. Source / GeoNet

They suspect the fresh activity is a result of magma moving around within it and jostling for space, possibly because of new magma coming up from below.

GNS Science senior volcano geophysicist Dr Craig Miller said that, five months in, this episode had reached the mid-range of how long comparable events lasted.

"But we're not anticipating it to stop, or anything like that – and there are international examples to support the fact that these things can go on for a while."

It was even possible, though less likely, that the activity might continue through summer and beyond.

Victoria University of Wellington volcano seismologist Dr Finn Illsley-Kemp said previous events tended to last between a few months and a year.

"So, we say see this current unrest continue for a few months to come," he said.

"On the other hand, it's also possible that the unrest has already peaked, and we will now see a steady decline to background levels of seismicity."

Miller pointed out that the intensity of the unrest could also keep fluctuating.

"You might see a die-off in activity one week, but then it picks up again the next," he said.

"So, we need to wait to make sure we're not just in a pause, and see a few months of low activity to be confident it was over."

If the unrest went the other way and escalated, it could lead to quakes large enough to cause ground shaking, landslides and liquefaction.

"Substantially higher levels of ground deformation - tens of centimetres or metres - would only occur at higher unrest levels, and could have impacts such as damaging underground services."

Source / GeoNet

The last episode, in 2019, included a 5.0 event that struck near Motutaiko Island, causing shaking from Turangi to Taupō.

"Earthquakes of this size or larger are always possible in the central North Island because of the tectonic Taupō rift," Illsley-Kemp said.

"But during this state of minor unrest the chances of a magnitude 5.0 earthquake, like in 2019, are increased.

"This could cause some damage, so people in the area should be prepared and if they feel a large earthquake remember to drop, cover, and hold."

Trying to predict what was likely to happen next at Taupō remained challenging, he said, given scientists could only refer to two events – 2008 and 2019 – with comparable levels of monitoring.

"This means that we can only see a limited snapshot of what unrest at Taupō can look like, and how long it can last," Illsley-Kemp said.

"This is a real difficulty for monitoring caldera volcanoes like Taupō worldwide, because the timeframes they operate on far exceed the time in which we've been collecting data."

Scientists were working hard to develop a range of possible future scenarios for Taupō – and an actual eruption remained a decidedly unlikely one.

Of 17 episodes in the past 150 years, none have ended with a big event.

One 2020 modelling study put the annual probability of a Taupō eruption at any size at a very low chance of one in 800 – or at between 0.5 and 1.3 per cent - within the next 500 years.

Source / GeoNet

Nonetheless, the volcano was ever-capable of generating enormous events, as it's done throughout its 300,000-year eruptive history.

Lake Taupō itself essentially fills the hole left by one of these - the gigantic Oruanui eruption around 25,400 years ago, in which more than 1100 cubic kilometres of pumice and ash was spewed into the planet's atmosphere.

Since then, there have been about 28 smaller ones we know of: the most recent being the Hatepe eruption 1800 years ago, which was still big enough to obliterate the surrounding landscape.