The Volcanic Alert Level for Taupō Volcano has been raised to level one after nearly 700 earthquakes were recorded since May.
There has been an increase in earthquakes and deformation (ground movement) at Taupō since May this year indicating volcanic unrest was occurring, GNS Science said in a statement today.
GNS had recorded almost 700 earthquakes mainly beneath Lake Taupō since May including a 4.2 magnitude shake on September 10.
This is the first time the alert level for the Taupō volcanic area has been raised to level one, despite there being 17 previous episodes of volcanic unrest in Taupō over the past 150 years, GNS said.
Several of these episodes were "more severe than what was currently being observed".
The Volcanic Alert Level [VAL] system is based on six levels, with the first level indicating minor volcanic unrest.
GNS Science Volcanologist Steven Sherburn said the system was introduced in late 1994 before the 1995-96 Ruapehu eruptions.
"The VAL system has been changed twice since then in response to our and stakeholders changing needs and capabilities. The current system has been in place since July 2014," Sherburn said.
"Our understanding of the current activity is informed by new knowledge of past unrest. It has been helped especially by analysis of the 2019 activity, but also activity in 2008, and another 17 unrest episodes over the past 150 years."
He said monitoring capability had also improved in the last decade or two.
"Had we known in 2019, 2008, and earlier what we know now, then it's possible the VAL may have been raised to VAL1 at those times too," he said.
"None of these episodes, or the many other episodes which would have occurred over the past 1800 years before written records were kept, ended in an eruption."
The last eruption at Taupō volcano was in 232 AD ± 10 years.
The chance of an eruption at Taupō remains very low in any one year, GNS said.
Earthquakes and deformation could continue in the area for the coming weeks or months, and while some of the earthquakes may be felt in areas around Lake Taupō, the
deformation was currently only detectable to sensitive monitoring instruments.
GNS said the Volcanic Alert Level reflected the current level of volcanic unrest or activity and was not a forecast of future activity.