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.
The authors of the paper note that there is “enough melt to support another supereruption” comparable to the one that formed LVC. However, they stress that the melt’s presence “no way ensures that the magma is eruptible.”
Magma isn't just molten fury, by the way: it's part solid, part liquid. Around 27 percent of the magma there is properly molten, which is shy of the 50 percent needed to trigger an eruption. It’s not even clear if the melt is arranged in a way that makes it more or less able to erupt en masse.
Dr Jessica Ball, a volcanologist at CalVO told IFLScience that “the cataclysmic Bishop Tuff eruption” and others like it nearby, “while large and impressive, are not the sort of thing that repeat themselves often.”
The USGS website explains that the next eruption in this complex volcanic chain will most likely be a very localized and small occurrence featuring steam blasts, some ashfall, and ballistics. Another common eruption type is lava dome eruptions, where viscous lava is extruded from a vent that can eventually burst explosively or in a collapsing fashion. None of these are anything like a supereruption.
This isn’t the first time that the molten parts of the material beneath LVC have been estimated, but this is essentially a very solid, high-resolution confirmation of what previous work has been indicating. Consequently, this informs risk assessment.
“In the short term, it doesn't change the kinds of hazards that people could potentially have to deal with in the LV region,” Ball, who isn’t directly involved in the new study, added. “What this study does do is bring us closer to accurate physics-based models of volcanic behavior, which could be used in a crisis situation or for long-term forecasting.”
So in summary, this paper isn’t worrying at all. It’s just demonstrating that the USGS are doing a spectacular job, as ever.
