How can geologists really know that there is a miniscule chance that the Yellowstone super volcano will erupt in the next few thousand years?
In: Earth Science
Since the parent comment is getting buried, thought I’d repost my response as a parent comment instead of reply.
Source: Getting my PhD in volcanology/igneous petrology studying the most recent Yellowstone supereruption (~630,000 years ago).
No, the chance of a supereruption is not quite a big chance. The chance of a rhyolitic lava flow that is not super destructive is higher.
The average, which is simply an average, is supereruptions occur every ~600,000 years. However, as with many things geology related, that is simply taking the interval between each one, adding them together, and dividing by the number of events. That’s not a good measure with many geologic events. There have been millions of years between supereruptions, and there have been <1 million years between eruptions.
However, the North American plate is moving ~10-11 cm/year over the Yellowstone hotspot. The continental crust is getting thicker and thicker over that area. The magma is also very high in silica which makes it much more viscous (much thicker and harder to erupt).
In order to have a volcanic eruption you need gasses (CO2, H2O…and more) to help the magma ascend and erupt. (Think about shaking a soda bottle. When you shake it, you release the CO2 from solution, remove the lid to remove pressure, and boom, you’re covered in soda.) The same is basically true for volcanoes. Now, make your soda a bit thicker than molasses, shake it with the same about of CO2 as your soda, it’s probably not going to explode when you remove the lid.
To erupt a magma such as that beneath Yellowstone, you need A LOT of gasses, and you need less pressure as well (a fault, a crack in the crust, some sort of weakness). Given that the crust is thicker now, it’s going to take A LOT of gas and a lot of energy to get that magma to the surface explosively.
This all means that a supereruption of Yellowstone in our lifetime (hell, maybe even human existence) is very slim. The more likely scenario is a lava flow that is extremely thick and slow moving that creates more of a dome in a very localized region of the park.
So, while the apocalyptic nature of a Yellowstone supereruption can be fun and frightening to think about, we’ll never see that scale of eruption from Yellowstone.
If you have questions about Yellowstone or volcanoes in general, I’m super happy to help answer those questions! I love this stuff!
*Edit to fix my viscosity mistake. The magma is more viscous. Thanks for all the replies catching that. Oops.
*Edit 2: The Cascade Volcano Observatory did a great AMA 2 years ago, you can check that out here: https://www.reddit.com/r/IAmA/comments/bole0q/were_us_volcano_experts_for_the_cascade_mountains/
*Edit 3: Check out the Caldera Chronicles where Yellowstone Volcano Observatory folks write articles for the public: https://www.usgs.gov/volcanoes/yellowstone/caldera-chronicles
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