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In a world I am building; Humanity has left the earth and now only the plants, animals and cities remain. Many animals continue life undisturbed, while other went extinct. But with the disappearance of humans, the sixth great extinction has begun to wind down and the Earth's animals are experiencing a time a great peace, but not for long. Only a few hundred years after humans leave, Yellowstone (the largest volcano on Earth) erupts.

Obviously, many species go into extinction; but what about the larger scale? How does this massive explosion of lava and ash do to the Earth as a whole?

It obviously differs from this question in that:

  1. That question relies on the effects of an earthquake on Yellowstone
  2. That question includes the existence of man on earth
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    $\begingroup$ The world will end. There is a discovery/national geographic documentary on it. $\endgroup$
    – NuWin
    Sep 19, 2016 at 2:29
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    $\begingroup$ @NuWin seems unlikely considering that volcanoes that big have occurred before and life still exists $\endgroup$
    – TrEs-2b
    Sep 19, 2016 at 3:44
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    $\begingroup$ Well I don't know about your world but in the real world if Yellowstone were to erupt, there would be mass extinction all over the planet. Everything will die, even animals in the ocean (although I think some small organisms will probably be able to withstand such an environment). BUT maybe in a few million years later, life can flourish again. $\endgroup$
    – NuWin
    Sep 19, 2016 at 3:52
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    $\begingroup$ Yellowstone has erupted several times before. See here: en.wikipedia.org/wiki/Yellowstone_Caldera I think Earth will survive, as it has in the past. $\endgroup$
    – a4android
    Sep 19, 2016 at 5:06
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    $\begingroup$ @NuWin: you're ridiculously wrong. The video you cite contradicts you as well. $\endgroup$
    – Michael Borgwardt
    Sep 19, 2016 at 8:29

4 Answers 4

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If a volcano erupts in the forest and there's nobody there to see it...

The post humanity nature of this question makes a big difference, what's left of the natural world will be thriving

BBC

Ash
Within 3-4 days, a fine dusting of ash could fall across Europe, according to a UK Met Office computer forecast commissioned by the BBC. The computer model predicts how ash would spread following a nine-day June eruption of 1000 cubic km of ash and gas from Yellowstone.

The model shows that the fallout from a Yellowstone super-eruption could affect three quarters of the US. The greatest danger would be within 1,000 km of the blast where 90 per cent of people could be killed.

Climate change
The most wide reaching effect of a Yellowstone eruption would be much colder weather.

Volcanoes can inject sulphur gas into the upper atmosphere, forming sulphuric acid aerosols that rapidly spread around the globe. Scientists believe sulphuric aerosols are the main cause of climatic cooling after an eruption.

Aerosols in the upper atmosphere would also scatter sunlight making the sky look like a cloudy winter morning all day long. The skies in Europe would appear red in the days after the eruption.

To predict how the climate may be affected, the BBC relied on historic data from the Toba supervolcano in Indonesia about 74,000 years ago and computer model forecasts commissioned from the UK Met Office and the Max Planck Institute in Hamburg.

Experts believe a Yellowstone eruption would inject 2,000 million tonnes of sulphur 40-50km above the Earth's surface. Once there it would take 2-3 weeks for the resulting sulphuric acid aerosols to cloak the globe – with devastating effects.

Global annual average temperatures would drop by up to 10 degrees, according to computer predictions. And the Northern Hemisphere could cool by up to 12 degrees. Experts say colder temperatures could last 6-10 years, gradually returning to normal

The climate change effect is largely dependent on how much damage humanity has done on the way out. If we've pushed up the temperatures a lot by the time we go, then the effect will be to bring them back down to where they should be, and as it all falls out it could end up being a great healer of the climate. If we've managed to control the damage then it could trigger a global ice age.

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    $\begingroup$ Reader please note that the temperature drop is in Celsius degrees, not Farenheiht. $\endgroup$
    – Mindwin Remember Monica
    Sep 19, 2016 at 13:22
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    $\begingroup$ @Mindwin, I forget half the readership still lives in the past ;) $\endgroup$
    – Separatrix
    Sep 19, 2016 at 13:26
  • $\begingroup$ you quoted verbatim, the BBC editor slipped the units. No wrong on your part. $\endgroup$
    – Mindwin Remember Monica
    Sep 19, 2016 at 13:44
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    $\begingroup$ It can make a good story to have a group of ekoterrorists trying to trigger Yellowstone to bring down temperatures caused by global warming :) $\endgroup$
    – roslav
    Sep 19, 2016 at 16:16
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    $\begingroup$ @roslav, go for it then, I expect a first draft on my desk by 1st November ;) $\endgroup$
    – Separatrix
    Sep 20, 2016 at 7:08
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The eruption would do absolutely nothing to "Earth as a whole". On a geological scale, it's a minor blip, nothing special. Has happened hundreds of times.

The effects it would have on the climate are rather difficult to predict, analyses of previous supervolcano eruption e.g. Lake Toba don't seem to agree well. They vary between "other parts of the world weren't affected very much" and "it triggered a 1000 year ice age".

At minimum you'd get a global average temperature drop of several degrees resulting in severe winters and lukewarm summers for a few years.

Of course, even that could easily be enough to wipe out many less adaptible species, but those that occur in a large geographic range would have a very good chance of surviving even a real ice age in some spots with more favorable conditions and have their population numbers recover afterwards.

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    $\begingroup$ What's an example of something that would affect Earth as a whole? Just things like creation of the moon or the sun swallowing Earth? $\endgroup$
    – djechlin
    Sep 19, 2016 at 18:41
  • $\begingroup$ There's a difference between affecting the Earth as a whole and something that has a serious effect. The effect of Yellowstone's eruption seems to be, "Not much, relatively speaking." $\endgroup$
    – Wayne Werner
    Sep 19, 2016 at 19:12
  • $\begingroup$ @djechlin - Google Year Without a Summer and pick one. All of those are volcanic climate events that changed the world. $\endgroup$
    – Mazura
    Sep 20, 2016 at 1:37
  • $\begingroup$ @Mazura sounds like Yellowstone eruption would be way, way more severe than the examples in your list. So that doesn't support this answer's "absolutely nothing" view. $\endgroup$
    – djechlin
    Sep 20, 2016 at 1:54
  • $\begingroup$ @djechlin - Replace "Earth" with humanity in the title and you might have something. But on a geological scale, you and I mean nothing. "relatively speaking" our lives are meaningless. relative to the Earth, not humanity. I think you're missing the tongue-in-cheek aspect of this answer. The Earth will still be here (for a while) after we've done our part to help destroy it. It will be a bad day, for us; Earth could care less. $\endgroup$
    – Mazura
    Sep 20, 2016 at 2:16
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Basically there would be a giant crater.

Then a debris field from covering most of western North America with a fall out distance of around Minnesota to Michigan.

Further, thee would be ash in the atmosphere that surrounds the Earth that lowers the temperature.

This would cause suffocation in the fallout area. Famine and long winters for a few decades. The worse part of it would be that those in North America that don't die imediately or starve will have a much higher chance of cancer due to the particles.

The US wouldn't be completely wiped out, but it would require a ton of aid. Canada would suffer less due to farther away and smaller population, but overall it would suffer too.

Secondary effect might be the triggering of San Andreas Faults, the Oil pipelines, the places used for fracking blowing up, Butane deposits blowing up, and Cumbre Vieja falling into the ocean causes by possible earth quakes... All of these are more or less likely to happen, but all could happen or none could. If they did all happen, the US would likely be blown off the map completely.

In other words, the threat that it poses is terrible, but not as terrible as once thought, since it was once thought that it would be a complete or near complete extinction event.

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    $\begingroup$ I clearly say in my question that this is post humanity, so no +1 for you, but as you more likely missed that, there is also no -1 for you $\endgroup$
    – TrEs-2b
    Sep 19, 2016 at 6:43
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    $\begingroup$ @UncleTres Very little changes with that. The oil pipelines and fracking won't break/blow up because they're not there. The effects this would have on humans is the same as animals so they suffocate and such just as well. $\endgroup$
    – Durakken
    Sep 19, 2016 at 6:57
  • $\begingroup$ Actually the effects would be a lot worse for humans since modern humans are having trouble adapting to survival scenarios. There not being any humans around doesn't make much of a difference since after the eruption there would no longer be humans one way or another. At least, USA side. The rest of the world is a different story. $\endgroup$
    – Mast
    Sep 19, 2016 at 10:02
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Well, whenever a volcano erupts, there is usually a measurable decrease in average temperature because of all the ash and gases in the atmosphere. Assuming that Yellowstone is one that erupts properly instead of just crumbles, it probably would drop temp significantly (possible into the next ice age).

Assume that most of the US and Canada and Mexico are blown away. This would cause tsunamis to slam into every coastline that you could you project a relatively straight line from the explosion. I'd probably say it would be coming at a couple hundred miles an hour and would wipe out everything from the shore to the mountain. It would also kick up a lot of stuff around, mixing up surface dirt, exposing other places to the bedrock, but also spreading the coastline out when the water drags everything with it as it recedes. That means you'll find buildings, artifacts, and stuff really far into the ocean.

Obviously, this will change global weather patterns because the Rocky Mountains wouldn't be there. That would cause changes to the air flow, weather, and precipitation. When the lava cools, it probably would create a new mountain range of rock, which means there would be a wasteland for quite a while.

Once the glaciers from the new ice age recede, there is probably going to be a new sea where Yellowstone was. It probably will also join in with the coastal ridge so you'd probably have the plate tectonics spreading away from that point instead of contracting toward it.

Having a big crater will also lower the ocean levels relatively quickly. How much? Not entirely sure. Some of it will be deposited on the existing continent that wasn't destroyed while more of it would return. I'd probably expected a few inches lower at least.

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    $\begingroup$ While I agree with many of your later points, I do not think that the vast majority of North America would be blown away. The explosion zone would be huge, but not that huge. The ash would cover a huge chunk of America though. I hadn't even thought of the lack of the rocky's, the wasteland of Yellowstone or the New sea though, So thanks for that. +1 $\endgroup$
    – TrEs-2b
    Sep 19, 2016 at 2:45
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    $\begingroup$ Actually this answer is way overblown, even for what was suggested a few years ago and estimates of the damage have been reduced since then. $\endgroup$
    – Durakken
    Sep 19, 2016 at 3:48
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    $\begingroup$ Tsunamis? From an inland eruption? An entire mountain range being destroyed by a caldera eruption in another part of the continent? A volcanic eruption of any kind forming a new sea or reversing the direction of plate movements? None of this has any basis in geology. The effects would be bad, mostly due to its effects on the atmosphere - but it would be nothing like what this misinformed answer describes. $\endgroup$
    – N. Virgo
    Sep 19, 2016 at 8:45

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