The Lake Taupō volcano caused the largest eruption on Earth in the past five millennia when it last exploded about 1800 years ago. Photo: RNZ / Rebekah Parsons-King
A volcano seismologist says the raising of the alert level for the Lake Taupō volcano from zero to one is more a sign of improved monitoring rather than unusual activity.
GNS Science says there has been an increase in earthquakes and ground movement at Taupō since May 2022 indicating volcanic unrest is occurring.
GeoNet has increased the alert level for the volcano below Lake Taupō for the first time, after a swarm of quakes around the lake this year.
The super-volcano has been rattled by 40 tremors a week since May, and 700 overall since January. The volcano caused the largest eruption on Earth in the past five millennia when it last exploded about 1800 years ago.
Victoria University of Wellington volcano seismologist Dr Finn Illsley-Kemp told Nine to Noon this kind of behaviour was not unusual for Taupō.
"For an eruption of any significance we do expect to get more warning in terms of signals" - Volcanologist Dr Finn Illsley-Kemp
The volcano has been exhibiting minor unrest activity since about May and seismologists have also recorded ground deformation, which means the ground under Taupō is inflating.
"The raise in the alert level yesterday just reflects our improved understanding of Taupō and also our improved monitoring so we're able to get more information in real time from Taupō.
"There's still many things we don't understand but we definitely have a feeling now that this volcano is active."
The volcano appears to have this level of "restless" behaviour about once a decade, Illsley-Kemp said.
Taupō is a Rhyolite volcano, which means the type of magma underneath the volcano is viscous and sticky.
That magma sits in a chamber at a depth of about 5km, he said.
"That magma is moving around, jostling for space.
"There might be some new magma that's coming into the bottom of it and adding some energy and temperature to it and that's causing it to kind of shake around and react to that impulse."
The reason behind the regularity of volcanic activity under Lake Taupō was not totally understood although he said it was not cause for concern.
It was difficult to compare the Lake Taupō volcano with others like Whakaari White Island and Mt Ruapehu as it operates on much longer time scales.
"We expect that a volcano like Taupō for an eruption of any significance we do expect to get more warning in terms of signals like these earthquakes and ground deformation that we've been seeing recently.
"We're less likely to get a kind of 'blue sky' eruption at Taupō that comes out of nowhere."
Scientists knew of 28 small eruptions at Taupō since the volcano had its last "very, very large" eruption about 25,000 years ago.
"The most recent which was 232 AD, so around 1800 years ago, that was also a very large eruption but apart from that all of those 28 other eruptions were much much smaller.
"So that's the a really key point with Taupō it's very very unlikely to erupt and even if does it's not likely to be one of those very large ones that people tend to think of at Taupō," Illsley-Kemp said.
It was difficult to estimate when the next eruption might occur as volcanoes don't build up energy in the way that earthquakes do, which makes it difficult to forecast when a volcanic event may occur.