Supervolcano in California is cooling, but still poses the threat of powerful earthquakes in the region

Caltech researchers used advanced imaging techniques to study increased seismic activity in California's Long Valley Caldera, a dormant supervolcano, reports TimesOfIndia.

Photo: IStock

A caldera is a vast cirque-shaped basin of volcanic origin, often with steep walls and a more or less flat bottom. Such a decrease in relief is formed on a volcano after the collapse of the crater walls or as a result of its catastrophic eruption.

Long Valley Caldera is one of the largest on our planet. Its appearance is associated with the eruption of a huge volcano that occurred about 760 thousand years ago. The volcanic activity was so colossal that the magma chamber below the summit was emptied to the point of collapse, and the now destroyed volcano literally collapsed into the ground.

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In May 1980, a series of large earthquakes of up to magnitude 6.0 occurred on the southern edge of Long Valley, associated with the growth of the resurgent dome. The ground in the caldera rose by 25 cm during that period, reports Vulcan. This event marked the beginning of an active period of unrest that continues to this day. Since then, constant tremors and ground uplift have been recorded in Long Valley, accompanied by changes in water temperature in hot springs and gas emissions.

Full picture

Now Caltech researchers have created detailed underground images of the Long Valley Caldera, going 10 kilometers into the Earth's crust.

The study, led by Professor Zhongwen Zhang, was published in the journal Science Advances on October 18.

“We don't think the region is preparing for another supervolcano eruption, but the cooling process could release enough gas and liquid to cause earthquakes and small eruptions,” Zhang says. “For example, in May 1980, four magnitude 6 earthquakes occurred in this region alone.”

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High-resolution images show the volcano's magma chamber is capped by a hardened cap of crystallized rock as liquid magma cools and solidifies.

Researchers make inferences about the subsurface environment by measuring seismic waves from earthquakes.

Zhang's team's method uses fiber optic cables similar to those used for Internet services. These cables support seismic measurements using distributed acoustic sensing (DAS).

The 100-kilometer cable they used to image Long Valley Caldera was equivalent to a string of 10 single-component seismometers. Over 000 months, the team measured more than 18 seismic events, most of which were too weak to be felt by humans.

This study marks the first time such deep, high-resolution images have been generated using DAS.

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Previous local tomography images were either limited to the shallow subsurface environment at a depth of about 5 kilometers, or covered a larger area at lower resolution.

“This is one of the first demonstrations of how DAS can change our understanding of crustal dynamics,” says Ettore Biondi, a DAS scientist at Caltech and first author of the paper. “We are excited to apply similar technology to other regions where we are interested in learning about subsurface information.”

The team's future plans include using a 200-kilometer cable to reach even deeper into the Earth's crust, reaching depths of about 15 to 20 kilometers where the caldera's magma chamber, its "beating heart," cools.

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