California's Largest Volcano Remains Active, But A New Study Says A Supereruption Is Unlikely

The U.S. Geological Survey deemed the Long Valley Caldera — adjacent to Mammoth Mountain — to be a "very high threat" in 2018. But a new study in the Science Advances journal suggests a catastrophic volcanic eruption is not likely.

The study's co-author and CalTech geophysics professor Zhongwen Zhan said sensors attached to the ends of fiber optic cables gave the team clear images of the magma chamber for the first time. Those images revealed 8 kilometers of rocks separating the magma chamber from the surface, which means a super eruption is unlikely.

The magma chamber is still releasing water and gas as it cools down. That activity causes seismic movement and deformation of the surface, but according to Zhan the activity remains hazardous.

"We don't need to worry about a big eruption," he said. "But something small in nature still could be something big for human being, right? For society."

The Long Valley Caldera is the largest volcano in California, according to Zhan. It had a super eruption around 720,000 years ago, comparable to the Yellowstone super eruption. But he says the caldera, which has been active since 1978, has been relatively quiet since.

Zhan said the Long Valley Caldera is also the first major imaging project using fiber optic cables. Given that there are thousands of miles of fibers, and knowing that the technology works well, he said the team plans to also study earthquakes and other volcanoes across the state.