A supervolcano in New Zealand has raged so hard that the ground above it is moving

(ORDO NEWS) — The vast expanses of sky-blue waters of Lake Taupo, topped by misty mountain horizons, evoke a feeling of extreme tranquility.

Deep underground, however, geological unrest is brewing, according to a new paper published in the New Zealand Journal of Geology and Geophysics.

Lake Taupo is the largest freshwater lake in Australasia, located in the center of New Zealand’s northern island. And although today it seems calm, the history of its occurrence was very turbulent.

The waters of the lake are in a prehistoric caldera – a word derived from the Spanish “cauldron” or “boiling cauldron” – formed during Earth’s last super-eruption, the Oruanui eruption, 25,400 years ago.

When magma is ejected from a supervolcano (defined as the ejection of at least 1,000 cubic kilometers of material in a single eruption) in an event like the Oruanui eruption, the depleted magma vents close, the Earth’s surface sinks, and the landscape becomes a caldera forever.

Over the past 12,000 years, the Taupo volcano has been active 25 times. Its last eruption in 232 AD is called by the authors of the new work “one of the most explosive eruptions on Earth in historical time.”

Since then, the volcano has had at least four documented “wave episodes” causing devastating earthquakes and, in 1922, massive subsidence.

The researchers studied more recent periods of unrest supervolcano by analyzing data for 42 years, collected at 22 objects located around and throughout the lake. And there is evidence that the supervolcano is still rumbling.

“In 1979, [researchers] began using a new survey technique that uses the surface of the lake to detect small changes, and since then, four surveys have been carried out each year,” said Finn Illsley-Kemp, lead author of the study, a seismologist at the University of Victoria at Wellington. the method involves the use of a pressure gauge that measures the vertical displacement of the lake bed.

To ensure data reliability, these gauges are weighted to reduce wave effects, and multiple measurements are taken for each data point to reveal degrees of variation and deviation. A backup pressure gauge is also installed at each site to provide insurance in case of disturbances from other forces.

At the start of the project, measurements were made using hand-held pressure gauges installed at only six stations. Eight more stations were added between August 1982 and July 1983, during which time the value of these measurements became apparent.

In early 1983, the system detected an increase or decrease in the water level in different areas. Shortly thereafter, a flurry of earthquakes rocked the region, causing several faults to rupture, causing the central Caiapo Fault Belt to sink and other sections at the south end of the lake to rise.

The 1983 earthquake swarm was only the first of seven separate episodes of unrest recorded over the past 35 years.

By 1986, routine surveys were being conducted each year with additional sensors and additional observations after earthquakes, creating a robust dataset that only became more detailed over time.

The authors observed that during periods of geological unrest, the northeastern end of the lake (which is closest to the center of the volcano and adjacent fault lines) tended to rise; the bottom of the lake near the center of the fault was sinking; and some subsidence was observed at the south end of the lake.

“Within the lake, near the Horomatanga reefs, the volcano caused a 160 mm [16 cm or 6.3 in] rise, while north of the lake, tectonic faults caused a 140 mm [5.5 in] subsidence,” Illsley said. Kemp.

He believes that this region, which has had very few earthquakes compared to the surrounding areas, is home to the Taupo magma reservoir, which contains deep rocks that are too hot and molten for earthquakes to occur.

The researchers say the 16cm rise, which while not catastrophic, is definitely enough to cause some damage to buildings or pipes, may be caused by magma moving closer to the surface during periods of unrest.

Illsley-Kemp said the study shows that Taupo is an active and dynamic volcano, closely related to the surrounding tectonics.

The researchers believe that the northeastern part of the volcano, where the youngest vents are located, is likely to be affected by the expansion of hot magma pushing the earth up.

They believe that the “sinking” center of the Taupo Fault and subsidence at the southern end of the lake are most likely caused by deep cooling of the magma (and hence shrinkage), tectonic widening of the fault, or both.

Illsley Kemp regularly reassures people that while the volcano is in a state of turbulence, there is no evidence that it will erupt anytime soon.

“However, Taupo is likely to erupt at some stage over the next few thousand years – and so it is important that we monitor and understand these periods of unrest so that we can quickly identify any signs that may indicate an upcoming eruption,” he said in an article published in the New Zealand Herald newspaper in 2021.

Ultimately, this study is more about understanding the normal “behavior” of a caldera, and what to look for when things get heated up.

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