Yellowstone National Park is the site of a large supervolcano that is somewhat due for an eruption in the geological near term. I have seen slides and discussions to the effect that large portions of the American central highlands and Midwest would be inundated by several dozen millimeters of ash in the event of a large eruption at this supervolcano. Widespread forest fires in the near region and subduction events triggered as a result of the eruption on the west coast also seem at least plausible.

Seismologists no doubt closely monitor this site; an impending eruption might be forecast by several months. Yet given the scale of this event, it is difficult to imagine any preventative efforts the country could take to wholly mitigate the negative effects of this kind of disaster, even with foreknowledge.

In the event we had some forewarning of the event,

  1. How would the USA fare?
  2. How would the world at large fare?
  3. As a side note, what would the disaster zone look like? Feel free to wax poetic.
  • $\begingroup$ 1.) Not well, 2.) IDK, 3.) probably covered in volcanic ash/nothing will be living there. But for real, good question. $\endgroup$
    – Jax
    Aug 22, 2016 at 15:07
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    $\begingroup$ @AdamWykes About a decade ago BBC and the Discovery Channel co-produced a docudrama entitled "Supervolcano." A lot of research was put into it involving many interviews with respective experts in various fields. It should be noted that the facts are sensationalized, but it's probably more accurate than what you will find from the members of WBing: en.wikipedia.org/wiki/Supervolcano_(film) $\endgroup$
    – Ranger
    Aug 22, 2016 at 16:12
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    $\begingroup$ IMO this is definitely answerable in its current state. $\endgroup$
    – Jax
    Aug 22, 2016 at 16:34
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    $\begingroup$ I've got two close votes... any idea why? $\endgroup$
    – Adam Wykes
    Aug 22, 2016 at 17:19
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    $\begingroup$ Reminder to close-voters... $\endgroup$
    – Frostfyre
    Aug 22, 2016 at 18:21

3 Answers 3


This would be really bad. The United States would experience short-medium term economic devastation and be hit by major economic aftershocks for many years thereafter.

Let’s make an assumption that there is broad scientific agreement that the eruption is definitely going to happen with a six month warning period (this is unlikely in practice, but a useful simplification for this exploration).

Given that this is pretty speculative and the geological record is likely to have substantial inaccuracies, we can’t be certain about the size or classifications of the affected areas. For a rough estimation, I’ll use this map:

enter image description here

(It's worth noting that the depiction of ash fall ranges here are not particularly detailed and somewhat optimistic. There's a more comprehensive exploration of potential ash levels in this paper.)

The kill zone covers most of three states. Fortunately these states are relatively sparsely populated, but you’re still looking at almost three million people. This region is going to experience pyroclastic flows and will be almost entirely unsurvivable. This means at least three million people will need to be evacuated with no expectation of their home, business, or town surviving the event.

The broader ash zones are going to experience levels of ash fall that will kill crops and animals, cause widespread roof collapse in buildings, and damage cars to the point of being unusable.

The rest of the country will also be affected with most of it seeing some amount of ash, which even in small amounts can cause electrical damage, invade homes, and contaminate water supplies.

This would be an economic disaster without precedent in recorded history.

Before the Eruption

The forewarning, while likely to save lives, will only compound the economic damage. In the year leading up to the explosion there will be immense anxiety as increasing numbers of scientists agree with the predictions. This will cause some people to flee the entire region in advance. Businesses will cease to open in that area and many might hastily relocate. This could cause the economies in anywhere from three to ten of the closest states to collapse before the eruption even happens.

Then there’s the matter of evacuating three million people. Where do you put them? How do you feed them? The pressure from relocating so many people will increase the load on other state economies. Unemployment will soar. And that only assumes that the three million in the kill zone are evacuated, when many more millions are likely to be mandatorily or voluntarily evacuated from other nearby areas. You’ll also have some people who won’t heed the warning — either they won’t believe that it’s going to happen or are simply unwilling to abandon their property for the life of a homeless refugee in some other state.

At this point there would probably be a nation-wide challenge to feed and house so many displaced people.

Post Eruption

It’s worth noting that we don’t know how long a potential eruption might last. A four day event should be simpler to handle than a month-long eruption that’s constantly spewing ash, but both would be devastating.

All non-emergency aircraft in the U.S. and Canada would be grounded for the duration of the event and for some time afterwards. Power outages would be nationwide and systemic damage to power lines could result in months without power for many people, particularly in the core ash fall regions. The areas with the most ash would also see roads and ground transportation become unusable. Forewarning should at least ensure that most are prepared for this, but it will still massively impede emergency services. Another major danger across the highest ash fall regions is roof collapse. The weight of ash will cause widespread damage and loss of life.

Many of these effects will be felt all the way out to the coasts, including in states already hit hard by managing refugees from the interior. Food shortages are almost a guarantee, even with preparation, and now you have to deal with the most catastrophic problem: the eruption and ash fall have just hit America’s heartland. Agriculture will be utterly devastated, with widespread crop failure and livestock death. Water will be polluted with ash and in many states the remaining population will be in full-on survival mode. Starvation is likely in some places along with major unrest. These problems would take years to resolve and the damage to some of these state economies could last decades. A severe economic depression is all but a certainty.

International Effects

These are more speculative. It is safe to say that stock markets would plunge throughout the forewarning period. This is unlikely to be limited to the U.S. since the forecast would be for widespread devastation of one of the world’s top economic powerhouses. This could have severe consequences on economies worldwide.

Canada would certainly share in some of this misery. Yellowstone is close to southwestern Canada and could see severe damage on par with many of the central states. This is actually pretty noteworthy as it could seriously limit Canada's ability to assist the U.S. in the aftermath.

Worldwide travel would probably be mostly unaffected. There may be cancellations out of an abundance of caution outside of the Americas during the event, but the ash cloud should not pose the same long-term problems it will cause in North America. Much of this depends on the actual ash cloud itself and may be impacted by the time of year.

The most troublesome international effect is the possibility for climate change. Substantially smaller eruptions such as Tambora in 1815 caused major global effects (the “year without a summer”) and Yellowstone would be far worse. Substantial cooling and even global circulation of ash could cause a global agricultural crisis that might exist for years and kill many, many more millions worldwide.

If you’re interested in what the aftermath would look like, I’d suggest looking up images from the 1980 Mt. St. Helens eruption. In short: a flattened, devastated wasteland.

  • $\begingroup$ Could you add speculation on the state of international travel, food supply, and credit? $\endgroup$
    – Adam Wykes
    Aug 22, 2016 at 19:33
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    $\begingroup$ @AdamWykes I added a bit about international travel, but food supplies and credit veer into speculation too much for me to feel like I can add anything meaningful. $\endgroup$
    – Avernium
    Aug 22, 2016 at 21:53
  • $\begingroup$ Thanks. I'll up vote and wait to see what others want to say. $\endgroup$
    – Adam Wykes
    Aug 22, 2016 at 22:04
  • $\begingroup$ Nobody will survive in the primary ash zone because the ash will turn into something like concrete during rains. The cellars will become tombs. Also, the little ice age that will begin in the months after the explosion will make ressettlement very difficult - depending on the cooling forced by the volcano the current interglacial period may end. $\endgroup$
    – Geronimo
    Dec 2, 2018 at 21:01

many stuff: it could crash the stock market, could cause an economical catastrophe because of closed airports due to the gas, which carries tiny stones in.

It would destroy american farmland, and would also plunge the world into a volcanic winter.

  • $\begingroup$ it could cause an economical catastrophe, and would close airports due to the gas, which has tiny stones in. it would destroy american farmland, and would also plunge the world into a volcanic winter $\endgroup$
    – Shark
    Feb 20, 2017 at 9:36

The United States are gone. I've read in a NatGeo about the volcano that ash fell all the way to Cuba in one of the Yellowstone explosions, covering almost completely the Mississipi basin. That means that the world just lost one of its granaries. It will take many years for american agriculture to restart. And that assuming that the eruption will be just a single big explosion without follow-up explosions spilling more ash.

Our current global food supply is alredy quite vulnerable and when food prices rise people start burning things, like in the Arab Spring, in Russia in 1917, and at this very moment in France. In the case of a Yellowstone eruption the food price WILL rise. A lot. Because the US is one of the greatest agricultural countries, exporting food to the whole world.

And with the global cooling, that may be big enough to end current interglacial period, other granaries will go offline - The european plains from France to the Caspian Sea, The Yellow River, The argentiean pampas and maybe the brazillian highlands.

So, what will happen? Long term social collapse as the heavily urbanized industrial civilization suffers from revolutions. Some of these revolutions will be successful, other will be crushed but none will solve the big issue: there is not enough food and it will be a long time before food production starts growing again. The only "good" things that the revolutions will accomplish is the killing of billions, reducing the pressure. I'm pretty sure that some first world countries will start nuking and gassing 3rd world countries to steal their farmlands in a few decades after the eruption.

About forewarning: Forewarning would allow the nations to stockpile food. If the geologist gave, say, six months before the explosion with the volcano giving clearly visible clues that it would really blow, some food would be stockpiled. In the case of the United States, machinery to clear and rebuild the roads and power lines as soon as possible, with fuel and spare parts. That would reduce how many people would die in the first months. The preparations would also involve calling home some troops, like the ones in Europe, and positioning them in strategic places of the country to impose order. At the same time, build up of an expeditionary force to take over by force of arms fertile lands (maybe the Congo basin?) The american people would be very motivated and there would be endless lines of voluntaries, looking for free meals in the army. About the rest of the world: Preparation is food stockpile, that would mean no exports. Without the granaries, like Brazil, USA, Argentina exporting, that would mean that by the time the volcano really explodes some countries will alredy have starving people. The chinese and the arabs in particular, will have problems.

  • $\begingroup$ Your answer should include mention of whether the forewarning will matter and if so, what effects would it have. $\endgroup$
    – Adam Wykes
    Dec 3, 2018 at 19:53

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