Have you ever heard of Long Valley Caldera (LVC), a veritable supervolcano in California? There’s a good chance you haven’t because the media’s supervolcanic obsession generally begins and ends with Yellowstone – where every single tiny non-exciting event there, or even nearby, triggers apocalyptic headlines.
It’s a shame really, because LVC is fascinating, and a new Geology study led by the United States Geological Survey’s (USGS) California Volcano Observatory (CalVO) adds a new chapter to its storied history. Specifically, there are around 1,000 cubic kilometers (about 240 cubic miles) of magma within its plumbing system.
For this study, 26 years’ worth of cutting-edge seismic data was used to build up a 3D image of the subterranean world. As explained here, seismic waves change depending on what type of material they pass through, which means geophysicists can use them to approximate what down there is molten, and what is solid – and, as is normal for magma reservoirs, what’s between the two.
Does this mean we’re all in danger? Of course not – it just means that we now have a better understanding of a gigantic system featuring plenty of individual volcanoes. It also doesn’t mean, as one tabloid reported, that scientists have just "discovered” a supervolcano in California, as the USGS has known about it for quite some time now.
Around 760,000 years ago, LVC’s cauldron-shaped 16 x 32 kilometer (10 x 20 mile) pit (its “caldera”) formed when thick, gas-rich magma explosively depressurized. Pyroclastic flows covered the region out to a distance of 50 kilometers (31 miles), and ashfall reached as far as Nebraska.
LVC, as aforementioned, is a supervolcano, and this eruption – the Bishop Tuff-forming event – was a supereruption. The new study suggests that there’s certainly a large volume of molten, and potentially eruptible material down there, but this isn't scary. It's just informative.
A “supervolcano” isn’t what you think it is. It means that, at least once in its lifetime, it violently erupted 1,000 cubic kilometers of fresh volcanic material. That’s it: it doesn’t mean in any way that it’ll ever do this again. Maybe it will, but maybe it’s semi-retired in the volcanological Olympics.