If I ask you to think of a  “supervolcano”, there’s a good chance the first example that pops  into your head is Yellowstone.

And yes, Yellowstone is famous for being the site of massive supervolcanic eruptions. But it’s not the only one.

In  fact, there are so many of these large volcanic systems  around the world, SciShow can do a whole list show and still  not have time to cover them all. These volcanoes have had some of the biggest eruptions in our planet's history. Eruptions that could cover an  entire country in ash, form massive volcanic craters, and have even  altered the course of entire species.

Here are four supervolcanos you’ve never heard of. [♪INTRO] First, for the sake of my continuing  career as a volcanic researcher, I need to mention that the term “supervolcano” is extremely controversial among volcanologists. Many volcanologists actually hate it! Myself included quite frankly.

There is a more real jargon term  called a supereruption, and there’s a specific threshold an eruption has  to meet before getting called that. But plenty of people in the media  don’t know that, so they’ll often call things supervolcanoes that have  never even had a supereruption. And for the volcanos that do have one, well, most only ever have one supereruption  in their entire history, making the term supervolcano pretty misleading.

Yellowstone is one of the  few that has had multiple, and even so, it’s not like it’s  been out there these last several millions of years having  supereruption after supereruption. Most Yellowstone eruptions are not supereruptions and its next one will probably  be pretty underwhelming. But however you feel about the word, I think all of the volcanoes we  talk about today are pretty super.

Including this first one. This is Mount Aso, located in southwest Japan. It’s pretty big for a volcano,  but it’s sitting in an even bigger volcanic crater which is the  24-kilometer wide Aso Caldera.

A caldera is a volcanic crater, and it’s created when part of the volcano collapses in on itself, usually either during or shortly  after the volcanic eruption. Think about it, most major cities  would fit inside that volcanic crater. In fact, there are multiple farms and pastures located within Aso Caldera’s boundaries.

So I guess the locals don’t  mind the 17 different volcanic cones that have also formed within the caldera, or the 38 different eruptions  that have happened since 1950. After all, humans have coexisted with  volcanoes for a really long time. One news outlet in particular has called Aso the “Supervolcanic “Hell” Caldera”, which I’m sure volcanologists  got a great laugh out of.

That's a joke, misinformation is no laughing matter and I take it very, very seriously. Of those 17 cones inside the Aso volcanic complex, only one of them is considered active. Its most recent eruption was in 2021.

But it wasn’t a particularly dangerous one. At least, not super eruption dangerous. So let’s turn back the clock  to about 90,000 years ago, when Aso had the last of its  four major eruptions that formed the actual  we-can-fit-a-city-inside-it caldera.

Volcanologists call this particular  eruption, rather uncreatively, Aso-4. Which frankly really undersells the  fact that it’s the second largest volcanic eruption Earth has experienced  over the last 100,000 years! In addition to helping make  a giant hole in the ground, Aso-4 produced more than 600 cubic  kilometers of volcanic material.

That’s enough to cover nearly the  entire Japanese Archipelago in anywhere from 15 centimeters to  several meters worth of ash and other volcanic material, depending  on its distance from the volcano. The amount of ash is important  not just because of the unfortunate life forms that have to deal with ash, but it's also a key indicator of a super eruption. Or at least, it’s one of the ways volcanologists categorize volcanic eruptions.

I’m talking about the Volcanic  Explosivity Index, or VEI. It's based on multiple different  factors like the volume of the ash that was erupted, the height  that the ash plume reached in the atmosphere, and how long it  took for that ash to be erupted. The volcano is then ranked on a scale  of 0 to 8 based on these factors.

The eruption from Mount  Vesuvius that buried Pompeii was a VEI 5, and so was Mount  St. Helens’s eruption in 1980. The three other caldera-forming eruptions Aso also experienced were somewhere  in the VEI 6 to 7 range.

If you’re a volcano that manages  to hit an 8, congratulations, you’ve officially qualified for  “super eruption” status, and Aso did that roughly 90,000 years ago  with Aso-4, then never did it again. Now, you might think that  having to hit an 8 out of 8 on the scale of explosivity means  that every super eruption that reaches an 8 has to also be maximum deadly. Apocalyptic, if you will.

But you would be wrong. In fact, no super eruption has ever been successfully linked to a global mass extinction. Scientists have tried, but the  evidence just doesn’t point that way.

Although that isn’t very  reassuring for any animals that live right next to the giant volcanoes. Which brings me to our next entry: Located in the middle of  New Zealand’s North Island, Taupo has had one VEI 8 super eruption, more than 25,000 years ago. It also had a VEI 7 eruption  almost 2,000 years ago.

And in addition to a massive  ash plume, the island residents had to contend with another  famous volcanic hazard. Some of the floor really did become lava. But I actually mean something  even more deadly than a lava flow, which is a pyroclastic flow.

This  is a dense hot mass of lava blocks, ash, and volcanic gases rushing down the slopes of the volcano at speeds up to 700 kilometers per hour, and temperatures over 800 degrees Celsius. Taupo’s super eruption produced  a pyroclastic flow that reached more than 100 kilometers  downhill from the volcano’s peak. After being blanketed by all  that ash and volcanic rock, many local animal and plant populations around the volcano did go extinct or  they were on the verge of it… but that's not the only major  impact that these eruptions had.

This is the North Island Brown Kiwi, and kiwis are really important in New Zealand, being the unofficial national bird and the nickname for the people who live there. But this particular species has a bit of a quirk in its genetics all  thanks to their volcano. There are four genetic lineages  that go across the island.

They’re similar enough to be  the same species, but they’re different enough that researchers  can tell that they’re distinct. And one group of scientists hypothesizes that Taupo is at least partially to blame. If you look at a map of where  Taupo sits on New Zealand's North Island, the caldera is  right in the center of it.

So when the eruptions  happened, different populations across the island became  completely isolated, and this allowed their genes to evolve  independently from one another. The researchers then ran multiple  simulations of what would have happened to the kiwi population  under different scenarios, with different barriers that might have prevented mixing between the different populations and might have led to their modern day differences. Most of the models suggested that the eruption was at least partially to blame.

Of course, to know for certain, you’d need some kind of time machine, but  this is a pretty good start. Now, I know what you’re thinking: what about the kiwis living in Taupo’s caldera? Well, there aren’t any.

Today, it’s a lake,which is actually  not unheard of for volcanoes. The famous Crater Lake in  Oregon is a caldera lake. These are so common that our  next volcano has a lake, too!

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The super eruption that helped  create the Atitlán Caldera in Guatemala happened about 85,000 years ago. Not only has it filled with water since then, younger volcanic features have  also formed inside the caldera, including something called a parasitic cone. Yes, it turns out volcanologists can be creative while naming things once in a while.

This is what we call it when a  secondary opening on the side of the main volcanic cone opens  up and allows lava to escape, building a separate small volcanic feature that feeds off the same magma like a parasite! There are also brand new larger  volcanoes within the caldera, just like they had at Aso. The tallest is the most active,  erupting as recently as 1853.

In fact, every volcano we’re talking about today is still considered active by volcanologists. Even the ones that haven’t  erupted in thousands of years. Now, full disclosure: what  qualifies as an active volcano has evolved a lot over time, and the term may be used slightly differently from country to country.

But according to the United  States Geological Survey, “active” means a volcano has erupted either  within the past 11,700 years… in other words, during our current geologic epoch called the Holocene… or that it shows signs of what  volcanologists call unrest. Think earthquakes, volcanic gas emissions, or new magma lifting up the floor  of the volcano, things like that. All those things make it active,  but none of that activity has to be on the scale of “the  world could end any minute”.

Speaking of which, we’ve finally arrived at one of the most notorious supereruptions in history. OK, so maybe you’ve heard of Mount Toba. If it sounds familiar, it might be because of the Toba Catastrophe Hypothesis.

This idea was proposed back in 1998, and suggested the super eruption of Toba around 74,000 years ago triggered a complete environmental collapse and pushed the population of ancient humans  almost to complete extinction. If you’re going to blame any  one supereruption for the perception that they always  cause global mass extinctions, Toba is probably the source  of that misinformation. But here’s the thing: Modern science has debunked most  of that original hypothesis.

The idea that Toba caused such  a catastrophe hinges on a real phenomenon called a volcanic  winter, where the ash and gases being erupted out of the volcano  forms a layer of aerosols in Earth's atmosphere that reflects  sunlight away from Earth’s surface. This is a possibility for  any large volcanic eruption, not just a supereruption, and can cause the regional or global temperature to drop. These lower temperatures then  go on to affect crop growth and cause food shortages, and often result in a much bigger death toll than  the eruption itself would.

According to the original hypothesis, Toba’s volcanic winter lasted as long as 10 years and its impacts lasted as much as 1,000 years. Based on those numbers, of course it could cause a global catastrophe. But as volcanologists have  continued to study Toba… and archeologists have continued to study the lives of ancient humans… both fields have found that  the evidence just isn’t there.

I mean, a super eruption definitely occurred. But studies of the sediment from that time don’t show any hints of major long term cooling. Studies tracking human population density show no significant differences  before versus after the eruption.

And studies of a lot of  other “supervolcanoes” across the globe are finding these  eruptions may not produce as many sun-reflecting aerosols  as we thought they would. The rating of a super eruption  is based largely on ash output, but it's not ash that determines  the severity of a volcanic winter. It's the amount of sulfur dioxide which leads to the formation of aerosols.

An eruption with a much smaller VEI rating… or one that’s so unexplosive it  doesn’t even get a VEI rating… could still produce a much worse volcanic winter if it has a  much higher sulfur output. And we know this because of  research on eruptions called flood basalts, which produce  basically no ash whatsoever, or very little, but put out  a ton of sulfur dioxide. The truth is studying large volcanic eruptions from this long ago is just really hard to do.

And our understanding of these  systems is going to change drastically over time as the  technology to do our research improves. There’s a lot of inaccurate information  out there about super eruptions, but the truth can actually be way more interesting than the stuff people make up. And I’m personally really grateful  that we probably don’t have to worry about super eruptions in  our lifetime, even if it would mean I don’t have to worry about saving  for retirement if we had one. [♪OUTRO]