Roughly every 100,000 years, our planet undergoes
one of the most-violent catastrophes imaginable. Supervolcanoes are to regular volcanoes what
supermassive black holes are to regular black holes or the Incredible Hulk is to Hulk Hogan. Bigger, badder, and infinitely more-terrifying. Capable of ejecting over 1,000 cubic kilometers
of material, even the smallest supervolcano dwarfs any eruption in human history. Mt St Helens, Krakatoa, Vesuvius… all are
mere sparks against such infernos. But while no supervolcano has erupted since
the dawn of civilization, that doesn’t mean they’re gone. If you live in America, you may have even
visited one. Yellowstone national park is famous for its
beauty. But just under the surface lies something
far uglier: a plume of molten rock that - were it to cause an eruption - could potentially
kill millions. Where did this supervolcano come from, how
likely is it to explode, and what would happen to the world if it did? Today, Geographics is uncovering Yellowstone’s
explosive past… and taking a glimpse into its apocalyptic future. The Exploding Earth On April 10, 1815, Tambora volcano in Indonesia
exploded with a force unprecedented in recorded history. Over 3 days, 175 cubic kilometers of debris
was ejected into the atmosphere atop a plume of ash 45km high. So much material was hurled into the sky that
it darkened the sun. The following year, 1816, would become known
as the Year Without a Summer - a year in which ice froze rivers in August, flooding destroyed
crops, and famine and disease ran riot. Thanks to these climactic effects, it’s
thought as many as 82,000 people across the globe died. It was by far the biggest eruption since the
dawn of human civilization, dwarfing even the Hekla 3 eruption that may have triggered
the Bronze Age Collapse. But here comes the kicker. This apocalyptic volcano that affected the
entire planet was just a regular ol’ volcano. By contrast, were a supervolcano to explode
today, it would make Tambora look like a Girl Scout bake sale. In the history of the Earth, there have been
around 50 known supereruptions. The most-recent occurred at New Zealand’s
Lake Taupo about 26,000 years ago. But while a video about Taupo’s explosive
past would be great, that’s not what we’re here to discuss today. No, we’re here to talk about the most-famous
supervolcano of them all: Yellowstone. To get an idea of the how the Yellowstone
supervolcano formed, you have to go back in time. Way, way back into prehistory. Until roughly 66 million years ago, the entire
Yellowstone area was covered by an inland sea. But then the Cenozoic era began, and brought
with it a burst of volcanic activity. Now, this was volcanic activity unrelated
to the modern supervolcano. But it did result in the Absaroka mountain
Range popping into existence, giving Yellowstone its northern and eastern borders. However, it was what happened some 49 million
years later that changed the park’s fate. If you’d been floating above the North American
continent and watching the millennia pass on fast forward, it would’ve looked like
a whole bunch of volcanoes suddenly started springing up around the Nevada, Oregon, and
Idaho border. Those volcanoes would’ve started marching
east, popping up one by one on an 800km journey toward northwest Wyoming. But this would’ve just been the view from
above. Underground, a very different story would’ve
been taking place. Rather than the volcanoes themselves marching
northeast, the reality was that the North American plate was slowly grinding southwest
over a sunken bubble of magma. Imagine a carpet being dragged across a warped
old wooden floor with a bump in it. As the carpet moves, the bump would stay in
the same place, making different parts of the carpet rise up at different times. In a very simple way, that was what was happening
in prehistoric America over millions of years. Finally, some 2.1 million years ago, that
bump found itself under a thin, threadbare piece of carpet marked Yellowstone. It’s at this point that things got interesting. Not long after the magma bump found itself
below Yellowstone, it gave its first supereruption. Since we don’t have any records of a supervolcano
blowing, we don’t know what it would’ve actually looked like. But we can guess. Over thousands of years, magma, water vapor,
and gasses would’ve built up inside the bump, until the pressure made it start to
grow. Stood on the ground, you would’ve seen a
dome, getting bigger and bigger. Finally, it would’ve gotten so big that
the edges started to tear, providing a release for the pressure below. By the time you noticed that, though, your
last chance to run would’ve been long gone. The first Yellowstone supereruption was almost
beyond comprehension. Over 6,000 times the size of Mt St Helens,
it released 2,500 cubic kilometers of debris. Over 15,000 square kilometers of North America
were coated in ash. Where the magma blew, the Earth collapsed,
forming a depression the size of Rhode Island. In the aftermath, the gasses expelled would’ve
dimmed the sun, plunging the entire planet into a winter that lasted for years. It was the first example of the supervolcano’s
raw power. It wouldn’t be the last. The Great Eruptions In its two million years of existence, the
Yellowstone supervolcano has never again erupted with the force of its first major blast. But even its two smaller supereruptions were
still what we’d call “pretty damn big.” Take the supereruption of 640,000 BC. The third of Yellowstone’s three major explosions,
it went up with the force of 2,500 Mt St Helens eruptions. That meant a plume of ash 30km high, so big
it left debris as far away as the Gulf of Mexico. It meant gigantic, superheated clouds of rock
and ash nearly 1,0000C hot sweeping across modern Wyoming, burying the land beneath a
layer over 100m deep. Anything within 1,000km of the eruption almost
certainly died. In the aftermath, another gigantic caldera
formed, this one capable of swallowing the whole of Samoa. Even the smallest of the three supereruptions,
the one that blew in between these two monsters, would’ve been an awe-inspiring sight to
behold. Well, at least until it would’ve until it
killed you. However, it would be wrong to think that the
Yellowstone volcano is only capable of planet-cooling blasts. Between 640,000 and 70,000 BC, some 80 eruptions
transformed the Yellowstone landscape. Although some created features we’d still
recognize today - like the Pitchstone Plateau - none of them were even close to being Tambora-sized,
let alone supereruptions. It’s here we get to one of the biggest misconceptions
about supervolcanoes: that, because of their size, anytime they blow it must be a supereruption. The reality is that most supervolcanoes only
rarely erupt at their full capacity. They’re far more likely to just sit there,
bubbling away, creating groovy effects on the surface. Yellowstone volcano is a prime example of
this. All those steam vents, hot springs, and mud
cauldrons you’ve seen in your auntie’s vacation photos? They’re all due to that great big magma
chamber we talked about earlier. Because the ground in Yellowstone is cracked,
water is constantly worming its way down to the magma, getting superheated, and shooting
right back up to the surface. The 300 geysers in Yellowstone park - over
half the total in the world - only exist because they’re on the surface of a volcano so big
you can’t even see it. So next time you roll out there in your RV
and watch Old Faithful do its thing, just remember that the supervolcano below isn’t
only good for inspiring scary YouTube documentaries. In fact, without that plume of molten rock
under Wyoming - a plume that stretches at least 960km down, and likely as far as 3,000km
- there wouldn’t be a national park for you to visit at all. That’s because it was these outside signs
of volcanic activity that made people think the area was worth preserving in the first
place. The Invisible Volcano On August 29, 1870, the gloriously be-moustached
Gustavus Doane scaled Mount Washburn. A Civil War veteran turned explorer, the 30-year
old Doane was in Wyoming as part of - as his name might suggest - the Washburn-Langford-Doane
expedition. At this point in American history, much of
the interior was still a fascinating mystery. The West had been tamed, but many of those
places lying between the coasts were still the 19th Century equivalent of an olde timey
map marked “Here be monsters”. It was a mere 43 years earlier that the first
description of Yellowstone had appeared in a newspaper; only 34 years earlier that the
first rough map had been made. In the decades since, trappers, explorers,
and one priest had visited the area, but the stories they brought back of the landscape
were too fantastical to be believed. At the moment Gustavus Doane started scrambling
up the side of his mountain, the average American’s opinion of Yellowstone was basically “what’s
Yellowstone?”. It was the Washburn-Langford-Doane expedition’s
task to make sure that changed. At long last, Doane reached the top of Mt
Washburn. All around him stretched the wilds of Wyoming,
the great, rugged view that would soon become known as Yellowstone national park. To the south, the Rocky Mountains rose and
fell, adding texture to the view. But there was an anomaly. As Doane squinted, he noticed there was a
break in the mountain range, a place where a flat circle of forest seemed to have been
crudely carved out the landscape. Not long after, the explorer recorded his
theory on it. “The great basin,” he wrote, “has been
formerly one vast crater of a now extinct volcano.” It was the first time in history anyone had
realized the explosive secret Yellowstone was hiding. Prior to Doane’s expedition, humans had
been coming to the Yellowstone region for thousands of years. We know this, because tools dating back to
9,000BC have been unearthed at sites across the park. Since they’re from so far back, though,
we have no idea who they belonged to. The name of the people that produced these
tools has been lost to time as effectively as if it had been written on paper then dropped
into a raging river. It wasn’t until the fifteenth century that
we got a Yellowstone-based culture that still survives. Known as the Shoshone or sometimes the Sheepeaters,
the tribe settled the park around 1400 AD. Quite what they made of all the strange lakes,
geysers, and hot rivers wasn’t recorded, but we can assume it probably blew their minds. That’s because minds being blown is a pretty
consistent feature of Yellowstone’s past. When the first white people arrived in Yellowstone
400 years after the Shoshone, their accounts were often laughed off by those living on
America’s coasts as the wild ravings of deluded woodsmen. The idea of hot rivers and jets of boiling
water was simply too far-fetched; like if someone told you today about a secret place
in Idaho with candy floss trees. It didn’t help that the government’s official
expedition to the area failed to reach it, leaving most people in the dark about the
awe-inspiring landscape. But as the 19th century rolled on, more explorers
and trappers started coming back from Yellowstone with similar tales, until it was decided this
mythic place needed to be surveyed properly. And so it was, in 1870, that both Doane’s
three-name expedition and the near-simultaneous Hayden expedition set off to uncover Yellowstone’s
secrets. In their own ways, both would transform how
humankind saw this remote corner of Wyoming. As Doane clambered back down Washburn Mountain
that hot day in 1870, he was heading back into a different world. When the Hayden expedition returned, it would
be with photographs and paintings of Yellowstone that would capture the public’s attention. It would be off the back of these images that
Congress acted, passing a bill signed into law on March 1, 1872, that made Yellowstone
one of the very first national parks in the world - possibly the very first (there’s
a contender in Mongolia that may have pipped it to the post). But it would be Doane who eventually made
the most intriguing contribution. The idea of a vast, dead volcano underneath
Yellowstone lingered in the imagination. For a long time - almost 8 decades in fact
- it was part of the lore of the park. But then, at some point in the mid-20th century,
people decided to check if the volcano really was as dead as Doane had claimed. What they eventually found would explode everything
America thought it knew about its favorite park. The Volcano Made Visible The fact that we ever discovered the truth
about Yellowstone is down almost entirely to two things: a lump of rock, and a disappointing
boat trip. Let’s start with the rock first. In the late 1950s, a Harvard grad student
named Francis "Joe" Boyd was poking around the park when he stumbled across something
called a welded tuff. Now, to you or me, a welded tuff would look
no different from any other lump of rock. But Boyd was a geologist, and to him a welded
tuff didn’t look like random rock. It looked like what it was: ash that had once
been burning hot before becoming compressed and solidifying. It also looked like something that had come
from a geologically recent eruption. But one rock, no matter how weird, does not
a theory prove. Even as two more welded tuffs were discovered
in Yellowstone park, the jury remained out. It would take a weird boat trip to change
that. Jump cut ahead to 1973. Bob Smith, another geologist, was boating
across Yellowstone Lake for some work when he came to an old dock. A couple of decades before, Smith had moored
his boat at this same dock, but now it was underwater and useless. What’s more, the treeline was flooded out
too. Being far brainier than us, Smith didn’t
just shrug this off as a weird thing and carry on with his life. Instead, he took a survey of the entire Hayden
Valley area, then compared it to data from 1923. What he found was jaw-dropping. The north end of Yellowstone Lake had risen
nearly 75cm, sending extra water flooding down the southern end and submerging the old
dock. There was only one reason the ground might
swell upwards like this. The volcano beneath Yellowstone must still
be alive. Smith’s findings caused a minor sensation. It helped that Smith was good at turning a
phrase, such as when he described Yellowstone as a “living, breathing caldera”. But it also helped that the park kept on doing
weird things. In the mid-1980s, there was a cluster of earthquakes,
after which the the ground settled back down again to the height it had been in 1923. Whatever was down there was like some great
beast, a modern Cthulhu, dreaming in his layer at R'lyeh. The only question was, what would happen when
it woke up? Over the next couple of decades, geologists,
volcanologists, and lots of other people with jobs ending in “ologist” studied the heck
out of Yellowstone. It’s during this time that the giant magma
plume was discovered. That the volcanic timeline from this video’s
first section was pieced together. Slowly, as the sheer size and power of the
Yellowstone volcano dawned, a term rose to describe it. A term that started as strictly unscientific,
but soon became so widely-used that science co-opted it: supervolcano. Barely had the apocalyptic connotations of
that term become clear when, in the mid-2000s, the ground started rising beneath Yellowstone
Lake again. But if you’re expecting to hear that we’re
now in the run up to an eruption… well, you’re about to be very disappointed. It’s been estimated that the odds of Yellowstone
erupting in any year are about 0.00014 percent. By way of comparison, it’s actually more
likely that another Chicxulub-sized asteroid will come slamming into Earth than it is that
Yellowstone will blow its top in our lifetimes. Even when it does finally blow again, the
odds are even-slimmer that it’ll be a supereruption. You may have seen claims that Yellowstone
erupts on a schedule and that we’re “overdue” another catastrophic eruption. But volcanoes - with rare exceptions - simply
don’t work like that. The boring truth is that Yellowstone probably
won’t go off for thousands more years and, when it does, it’ll likely be a lava flow
that’s destructive within the park itself, but barely noticeable for the world at large. That being said, though, there is still the
tiniest, tiniest chance that the big one really could happen. And if it did… Well, let’s just say it’s time for this
video to take a turn into the speculative. It’s time for us to witness America’s
Armageddon. The World on Fire Because no supervolcano has erupted in recorded
history, we don’t really know what it would look like if Yellowstone suddenly went Old
Testament on America’s ass. But we can make some educated guesses. For instance, it seems reasonable to assume
that the ground around Yellowstone Lake would start swelling again, doming upwards as magma
rose into the chamber. Quite possibly, this dome would rise on a
scale we’ve never witnessed before. With the ground heaving upwards, we’d start
to get earthquakes, as the magma pushed solid rock out of its way to get to the surface. The closer we got to lift-off, the shallower
these earthquakes would get. Pretty soon they’d likely be detected across
the entire park, along with a sharp and sudden increase in CO2. In other words, we’d probably have some
pretty distinct warning signs. But that almost wouldn’t matter. Because when the magma finally reached the
surface, we’d hit midnight on the doomsday clock. Assuming an eruption as big as Yellowstone’s
last supereruption, the effects would be devastating beyond belief. Lava would inundate the park within a radius
of roughly 65km. This would suck for campers, but the real
problem wouldn’t be on the ground. It’d be in the air. Thousands of cubic kilometers of volcanic
ash would be blasted high over Wyoming. What happened next would depend a lot on the
wind, but one likely outcome would be a layer almost a meter thick settling over most of
Wyoming, Colorado, Montana, Idaho, and Utah. This wouldn’t be like a layer of snow. Just 30cm of ash can collapse a rooftop. Every water supply it touched would be poisoned. But it’s not like anyone would be around
to worry about it, apart from a few unfortunate survivors. Within 1,000km of the blast, it’s estimated
that 90 percent of people would be killed. A quick, back of an envelope calculation puts
that at north of 10 million people dead. And Yellowstone would just be getting started. As the ash traveled, it would blanket the
Midwest. Not deep enough to crush buildings, but deep
enough to cause large-scale crop failures and to make travel - and thus escape - an
impossibility. It would also be thick enough to cause major
respiratory problems in anyone caught outside. As the BBC once memorably put it: “Inhaled ash forms a cement-like mixture
in human lungs.” Yuck. By the time you reached the East Coast, the
ash layer would be a single centimeter thick. Even at this thinness, though, it would badly
disrupt travel, which would in turn mess up supply chains. Overall, its estimated that three quarters
of the USA would be plunged into a deranged, post-apocalyptic fantasy. And that would just be for starters. Over the coming days, the ash from Yellowstone
would drift across the Atlantic, until it also coated Europe. Remember the Icelandic eruption in April,
2010, that grounded every single plane on the continent? Well that would happen all over again. While actual damage in Europe would be minimal,
the economic cost would be enormous. Finally, once three weeks had passed, the
gasses unleashed into the atmosphere by Yellowstone would have completely shrouded the planet. When Tambora erupted in 1815, causing the
Year Without a Summer, it cooled the planet by something like 1.7C. A Yellowstone eruption, on the other hand,
would cool the planet by up to 12 degrees C. Nor would the effects only last a year. Were Yellowstone to blow today, the 2020s
would become known as the Decade without a summer. Ten whole years in which every day was like
a wet November in northern England. Crops would fail. The Monsoon would be disrupted, causing mass-starvation
in Asia. When the aftereffects finally faded, the sun
would shine back down on a planet - on a human civilization - that had been irrevocably changed. But it would also shine down on a human race
that was still alive. Yep, it would be a decade of catastrophe,
misery, and really awful experiences, but it wouldn’t be the end of the world. It’s not even a sure bet that it would be
the end of the USA. Back in the Cold War, government scientists
estimated that losing a quarter of America’s population in a nuclear exchange still wouldn’t
be enough to destroy the United States as a political entity. In the aftermath of a Yellowstone supereruption,
the US would slowly, surely, rebuild from its Armageddon. It might take decades. It might take centuries. But, in the end, the most-devastating eruption
in human history would fade into memory just as surely as the Black Death or Napoleonic
Wars. But this most probably won’t happen. As the American continent continues to move
southwest, the magma chamber has found itself no longer under Yellowstone’s thin Basin
crust, but under the thicker crust of the Rockies. This could be enough to keep the supervolcano
bottled up now forever. So that’s it then, the history of both Yellowstone
Park, and the volcano sleeping beneath it. The volcano that will almost certainly never
blow. But if you do one day find yourself in northwest
Wyoming, and hear reports about the ground rising up wildly… and earthquakes getting
shallower and shallower… and CO2 escaping across the park… Then don’t run. Just close your eyes, cross your fingers,
and pray. Because if the big one is coming - and that’s
still a pretty big if - there’ll be nothing else that you can possibly do.
