A supervolcano's alert level has been raised from 0 to 1 for the first time today, following a series of small earthquakes.
Scientists in New Zealand have emphasised that despite their concerns, the chance of an eruption of North Island's Taupō volcano "remains very low".
In fact, the last eruption happened nearly 1,800 years ago.
Geological agency, GeoNet, said that nearly 700 small earthquakes have been recorded at Lake Taupō - which is a large crater lake situated in the centre of New Zealand's North Island - since May this year.
While many of them were too weak to be felt on land, the largest was a 4.5-magnitude quake on September 10.
However GeoNet said that today was the first time it had raised the Taupo Volcano alert level, adding: "The earthquakes and deformation could continue for the coming weeks or months".
The ground deformation around the lake, Horomatangi Reef, has been also been observed. It is believed that the existing magmatic system is located there, and where most quakes have been recorded.
Speaking about their warning, the agency said: “We interpret the ground uplift and earthquake activity to be caused by the movement of magma and the hydrothermal fluids inside the volcano.
“We have also sampled springs and gas vents around the lake for changes in chemistry that may be related to the earthquake and ground uplift.”
GNS Science Volcanology Team Leader, Nico Fournier added: “While some of the earthquakes may be felt in areas around Lake Taupo, the deformation is currently only detectable by our sensitive monitoring instruments."
He continued: “We interpret the ground uplift and earthquake activity to be caused by the movement of magma and the hydrothermal fluids inside the volcano.
"We have also sampled springs and gas vents around the lake for changes in chemistry that may be related to the earthquake and ground uplift."
As a result of this, the volcanic level alert has been raised for the first time since they were introduced in 1994. The system itself has six levels - ranging from 0 to 5 - although an eruption is possible at any level.
Since 1870, there have been 17 episodes of unrest at Taupō - including four which could have been classified at alert level two - if the system had existed, according to GeoNet. Although, none of those events caused an eruption.
GeoNet said in Tuesday’s statement: “The Volcanic Alert Level reflects the current level of volcanic unrest or activity and is not a forecast of future activity.
“Volcanic unrest at volcanoes like Taupō could continue for months or years and not result in an eruption.”
Nearly 1,800 years ago, Taupō Volcano caused the largest eruption on Earth in the past 5,000 years when it exploded. Parts of the North Island were covered in at least 1 cm of ash, and lakeside areas were covered in tens of metres of rock and pyroclastic flow.
However, an even bigger eruption occurred at the volcano about 25,500 years ago - creating a large basin that formed much of the present lake shape.
Between these two events, at least 27 other eruptions have happened, with many being of a smaller scale.
New Zealand straddles the boundary between the Pacific and Australian tectonic plates, meaning it experiences significant volcanism and earthquakes.
In 2019, also on the North Island, active stratovolcano known as Whakaari/ White Island erupted while 47 tourists and guides were on the island at the time. Tragically, 22 people lost their lives and 25 were seriously injured.
In the aftermath of the tragedy, visits to the island were suspended.
