Yellowstone National Park is justly famous for its geysers, steaming pools and mudpots. The hot geologic features of the park are the remnants of three enormous volcanic explosions that left three calderas covering nearly 1,000 square miles. Underlain by large magma bodies not far from the surface, the Yellowstone area has the capability of sending massive amounts of lava and ash skyward, and its three known megablasts have dwarfed the most massive volcanic events in human history. In one, vulcanologists estimate that 585 cubic miles of material was ejected from the caldera. The ash from that event can be found from Iowa to Ventura.
All the drivers of those earlier explosions are still functioning under the very popular national park visited by millions. How likely is it that another such event threatens those tourists snapping photos of Old Faithful or the Grand Canyon of the Yellowstone? News reports seem to pop up every so often warning of a huge eruption that will take out half of the U.S. The reality is a bit less horrific. But just a bit less. Scientists at Yellowstone say that even if an event to rival the Big Three were to happen, it wouldn’t bury the nation under lava coast to coast. Yellowstone itself could easily be turned into a smoking hole, and lava might be seen to roll across the landscape for a 30 or 40 mile radius. But the major factor would be ash. For a radius of 500 miles or so, a layer of at least ten centimeters of gray ash (and far more, closer in) could coat the land, covering farmland, clogging waterways, collapsing roofs, and burying roads. The effect wouldn’t be flaming hot death but an incredible nuisance and an economic disaster, grounding planes and disrupting or destroying food growing ability in one of the world’s most productive agricultural regions. Weather would also be affected, but given the cooling effect, it might give a brief period of relief from global warming.
Opinions seem to differ, but it doesn’t appear that such a catastrophic event would spring itself upon us without warning. Moving magma pushes the brittle crust of the Earth, causing earthquakes of increasing magnitudes, and the rising heat source would fuel a lot of increased geothermal activity. It’s likely there would be time to get out of the way of the blast, maybe even weeks or months worth of it. Some evidence of crystals associated with the earlier eruptions, however, present evidence that the upwelling magma didn’t spend much time cooling as it came to the surface, so there is some debate, but big events usually send some signals, if we know how to read them.
Lastly, what is the likelihood of any of this happening any time soon? The three previous big shows ocurred 2.1 million, 1.3 million, and 640,000 years ago. So if you do the math and the clock is reliable, 640,000 years is about how often they occur. We would appear to be due, but nature doesn’t always follow a schedule; pressure releases along the millennia can extend the periods between events. If the schedule is extended by, say, ten thousand years, we don’t have much to worry about. The potential is certainly there, but other more predictable disasters are probably of more pressing concern.