In the Eastern Sierra Nevada mountains of California, a region known as the Long Valley Caldera has been exhibiting signs of unrest since the 1980s. This area, which sits atop a dormant supervolcano, has experienced swarms of earthquakes and ground inflation of nearly half an inch per year during these periods.
These signs of unrest indicate magma rising from deep within the Earth’s crust to form a new volcano. Scientists are monitoring the volcano closely and have found that although an eruption is not imminent, the chances of a major eruption over the next few years are high.
A supervolcano is a large, active volcano with magma below the surface that builds up over time until there is a significant release of lava and gas. These eruptions can be explosive, spewing lava, ash, and other debris far into the air. Volcanoes can form on land or underwater and can be small, medium, or large.
During this latest period of unrest, the magma has been building up inside a massive depression in the Earth called the caldera, which is formed when a volcanic explosion fills a crack in the Earth’s crust with liquid rock that cools and solidifies into a crater-shaped hole or basin.
The caldera beneath the Long Valley area is filled with rhyolite, three-fourths silica, and less brittle than other rock types. The rhyolite is thicker than most magma, which means that the magma can hold more gases. This is important because gasses can trigger seismic activity and can build up pressure in the magma, causing it to burst through the brittle lid of crystallized rhyolite.
An eruption of the Long Valley Caldera or its smaller neighbor, the Mono-Inyo Craters chain, could cause a dangerous situation. The eruption could cause a massive cloud of ash to cover the Western United States, and if the eruption is vast, it could bury the entire nation under a layer of ash up to six miles thick. The USGS monitors these areas and plans emergency responses if an eruption is likely to happen.
But if an eruption were to happen, it would likely be much lesser magnitude than the explosive supereruption that spewed 650 cubic kilometers of ash into the air during the eruption 760,000 years ago. Still, a large eruption from either of these calderas could significantly damage the resort town of Mammoth Lakes in the center of the Long Valley area and potentially to other towns along the route of ejected ash.
To learn more about what might be causing the current unrest, scientists at Caltech have created some of the most detailed underground images of these volcanoes yet. The work, led by Zhongwen Zhan (PhD’ 14), professor of geophysics, was published on October 18 in Science Advances. The high-resolution images are similar to those that were recently made of the Campi Flegrei, an Italian volcano that is currently in a state of active unrest.
