# How can geologists really know that there is a miniscule chance that the Yellowstone super volcano will erupt in the next few thousand years?

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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

Based on a geological history of it. And it’s not a “miniscule” chance – it is quite a big chance or rather with the cycle of some hundred thousands years it is expected to erupt sooner than later.

To explode the rock under the ground needs to be more lava. Currently all of the rock is actually rock. We would begin to see more activity and magma prior to an explosion. This change would take a long time. Therefore we know it’s not happening anytime soon.

They know from geological evidence that it erupts periodically. Deposits of certain types of rocks and minerals at certain depths, or in certain places, stuff like that. Most geological events occur periodically, and consistently.

In geological terms “periodically” is a very long time. Thousands, millions, or even billions of years, depending on the event in question. “Soon” has a similar time scale. Because the timeframe in question is so long, they could be off by less than 1% and miss the date by *millions* of years.

They know that the last eruption was some number of years ago, less than the usual amount of time between eruptions. Because it hasn’t happened yet, they know that it will happen again, and because the timeframe is so large, they can confidently say that it will happen again “soon” and be right.

For a smaller timeframe example, look at Old Faithful, also in Yellowstone. We know it erupts as frequently as it does because it happens so often that we can see it, that’s our evidence. It also does it regularly, it’s “periodically” just happens to be very short.

Take that idea and extrapolate it out to a billion year time scale. That’s the super volcano.

Not a geologist, but it sounds a lot like an interesting realization in probability theory where the probability of a single eruption in any given year is minuscule but over thousands of years the probability of a single eruption is higher

There needs to be enough lava built up to lead to the eruption and lave isn’t building up and is making no sign over the recorded history of Yellowstone of starting the necessary buildup. There are two domes that did build up in a series of eruptions from 170,000 years ago to 70,000 years ago, but they have been quiet since then.

Based on where things were at prior major eruption points, it seems pretty quiet.

Pro tip. If you say there’s a miniscule chance of something happening and it doesn’t happen.. nobody will question it

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

We know the statistical chance by counting the time between previous eruptions. The time between eruptions has been found to be very long, 1 to 2 million years, and the last eruption was half a million years ago, so any given day has only a tiny chance of being the big day of the eruption.

Same reason Nintendo ‘insiders’ know that Switch Pro is coming: It has to happen eventually.