The lake bed of one of the world’s most dangerous supervolcanoes – Lake Taupō in New Zealand – is constantly rising and falling, proving the volcano is still very active, nearly half a century of data has revealed.
Taupō, a caldera volcano and the site of New Zealand’s largest lake, has been active 25 times over the past 12,000 years. It is responsible for one of the largest explosive eruptions in recent human history: eruption AD232 which sent 120 km3 of pumice and ash into the atmosphere.
In 1979, scientists started an experimental project to monitor lake levels to detect volcanic and tectonic changes. To do this, the researchers set up fixed sounding stations around the lake, on the beaches, on the cliffs, on the piers and on a specially designed platform on the Horomatangi reef, the main vent of the 232 eruption. .
The team hung specially designed water gauges from 22 fixed points and used the specially designed platform to account for changes in lake level. This method enabled them to detect station height changes as small as 8 mm.
“We suspected that, if the volcano was active, this system might be able to detect small changes [vertical deformation] as the magma moved,” said Peter Otway, who has been involved with the project since its inception and is a lead author of the paper, published in the New Zealand Journal of Geology and Geophysics.
Otway also hoped to detect deformation due to tectonic stretching, which was known to have caused subsidence and a prolonged swarm of earthquakes in 1922.
The early years of monitoring produced nothing particularly exciting for researchers. But Otway’s luck suddenly changed in early 1983.
“My Kinloch Station [10km west of the town of Taupō]which had been declining very slowly, began to increase steadily, finally reaching 50mm by mid-June, by which time I had published a series of reports,” he said.
“Then, lo and behold, a lady from Kinloch phoned the office to say she had been nearly knocked out of her bath by an earthquake, soon followed by a flood of earthquake reports – instead of any seismograph standing at the time.”
The lake-leveling surveys had apparently made New Zealand’s first detection of pre-earthquake deformation – “the holy grail of predicting tectonic earthquakes”, Otway said.
After further analysis, the team realized that the earthquake swarm was due to volcanic activity rather than tectonic activity, as originally thought. But all was not lost – it is still considered the best example of volcanic unrest recorded by the program, he said.
The 43-year-old dataset has since shown that movements of magma and tectonic faulting below the surface frequently cause the ground surface above the volcano to rise and fall, said Dr Finnigan Illsley-Kemp , postdoctoral fellow in volcanic geodynamics at the University of Victoria. of Wellington and a co-author on the paper.
“In the lake near Horomatangi Reefs, the volcano caused 160mm of uplift, while north of the lake tectonic faulting caused 140mm of subsidence,” he said.
The program has helped prove, along with satellite and seismic monitoring, that Taupō is still an active volcano, with occasional periods of unrest as it slowly but steadily swells, Otway said.
“We would expect inflation to [the increasing pressure in the magma that can cause the surface to bulge] to accelerate rapidly before the next eruption, it is therefore essential that the deformation continues to be closely monitored.
But the evidence that one of the world’s supervolcanoes is steadily swelling is not alarming, said Eleanor Mestel, another co-author and PhD researcher at Victoria University.
“That’s the first thing people ask me at the Taupō gas station,” Mestel said. “I say: ‘eventually yes, but not now’.
“Volcanoes move naturally in their sleep. It is normal to have earthquakes and ground movements, especially large volcanoes like this. It doesn’t mean he wakes up and he’s going to burst.