They are eruptions so vast, so Earth-shattering, they have changed the history of our planet.
Climate collapse.
Toxic turmoil.
Mass extinction.
Worse than a killer asteroid, or nuclear war, they are Earth's most destructive Supervolcanoes.
North America, the time was six hundred and forty thousand years ago, long before humans
arrived on the continent.
Amid one of nature's great mountain building projects, the Rockies, vast columns of smoke
began to rise high into the atmosphere.
And soon a smokey haze wrapped the globe.
A thick blanket of ashe spread over the western United States.
Geologists have traced this event to a depression in the land known as a caldera, in the heart
of Yellowstone National Park in Wyoming.
Today, we venture to Yellowstone to admire its spectacles of steam and boiling mud.
All around, thermal energy is underfoot, like a pressure cooker gathering steam.
The heat escapes in an array of smoldering caldrons, steam vents, and hot springs, like
the famous Grand Prismatic.
Here, superheated water rises up from deep below ground, then cools and sinks back down
in a constant cycle.
Geysers are powered by boiling water that moves up through constricted channels in the
rocks.
When enough pressure builds, steam and water escape in jets that can blast high into the
air.
Along the Yellowstone River, heat welling up from below softened the underlying rocks
to such an extent that water released by rapid melting at the end of last ice age was able
to carve out one of the most spectacular river canyons in the world.
Visitors to Yellowstone may never suspect they are atop one of the world's largest active
volcanoes.
The last time it blew, it sent an estimated 1000 cubic kilometers of dirt, rocks, ashe,
dust, and soot into the atmosphere.
It's difficult to grasp the sheer scale of that eruption.
Compare it to recent experience.
In 1980, Mt.
St Helens blasted out just 2.79 cubic kilometers of ashe, less than three tenths of a percent
of what Yellowstone ejected.
In 1991, Mt.
Pinatubo in the Philippines released 10 cubic kilometers of material, along with 20 million
tons of sulfur dioxide.
A volcano twice that size blew up on the Indonesian island of Krakatoa in 1883.
It unleashed the equivalent force of 10,000 Hiroshima bombs, and tsunamis that killed
36,000 people.
The same year, the Norwegian artist Edvard Munch painted The Scream, with a sunset likely
inspired by the effects of smoke from Krakatoa.
"Clouds like blood and tongues of fire," he wrote, "hung above the blue-black fjord and
the city.''
This is Anak Krakatoa, or child of Krakatoa, an island that has risen in the years since.
It is a modest but unruly cone that may be building again toward another big one some
time in the future.
The modern standard was set by the eruption of Tambora, eight times larger than Krakatoa,
in 1815.
In its aftermath, 1816 became known as the "Year Without a Summer."
Crops failed and livestock died in much of the Northern Hemisphere, resulting in the
worst famine of the 19th century.
The public has long been aware of the hazards of an erupting volcano: explosions, lava,
and debris flows, like the ones dramatized in the movie Dante's Peak.
The record of recent volcanoes, from Tambora to Pinatubo, has added an additional global
hazard.
In these images captured by astronauts aboard the space shuttle, you can see the sulfurous
haze that covered the Earth in Pinatubo's wake.
It blocked enough sunlight to send global temperatures down by about a half a degree
Celsius.
Mt.
Pinatubo erupted at a time when scientists had begun to use high-powered computers to
model the response of Earth's climate to large-scale disruptions.
Based on their success modeling the circulation of particles from Pinatubo, one group sought
to explore the consequences of another type of eruption: limited nuclear war.
They focused on India and Pakistan, two countries that were engaged in a nuclear arms race.
The experiment assumed 100 Hiroshima-sized bombs.
The intense heat of cities burning sent over five million tons of smoke rising into the
stratosphere.
With no rain at that altitude to bring them down, soot particles lingered for years.
They absorbed far more solar radiation than the brighter sulfuric acid particles emitted
by volcanoes.
As a result, according to the study, global temperatures dropped by 1.2 degrees Celsius,
equivalent to the "Year without a summer" after Tambora.
That shortened the next growing season by 10-30 days, resulting in widespread crop failures.
Finally, in two to three years, the smoke began to clear and the climate steadily recovered.
But those impacts are dwarfed by what would happen in the wake of a supervolcano.
Take the last major Yellowstone eruption, 640 thousand years ago.
Scientists at the Max Planck Institute in Germany used an ensemble of computer models
to study its impact on Earth's climate.
Their virtual eruption sends up a giant cloud of ashe and dust that's taken by high altitude
prevailing winds.
In a month's time, the cloud has spread over much of the northern hemisphere.
The simulation tracks the bitter consequences.
Solar radiation at Earth's surface falls off in an uneven pattern.
The darkest point occurs around 18 months after the eruption, with the mid latitudes
of North America and Europe experiencing a steep drop in sunlight.
Air temperatures fall too, hitting their lowest point at 18 months.
In some places, they fall by an average of 10 degrees celsius.
That leads to the rapid growth of sea ice in the Artic.
More sea ice means that the Earth reflects even more solar energy back into space.
With cooler surface temperatures, rainfall levels decline and oceans and land areas retain
more carbon dioxide.
These factors all lead to a drop in biological productivity.
With food supplies lasting just weeks or days in some regions, human populations would be
subject to serious losses.
From their steep initial drop, average global temperatures recover gradually, approaching
pre-eruption levels only after two decades.
The study found that changes to the rate carbon is taken up and released back into the air
lasts even longer, two centuries.
As powerful as the Yellowstone eruption was, it still does not approach the greatest supervolcanoes
in history.
This is Toba, a large mountain lake on the Indonesian island of Sumatra.
It's the crater left behind by a super eruption 74,000 years ago.
What made Toba super is the sheer scale of the eruption.
Over fourteen terrible days, Toba blasted 2,800 cubic kilometers of material into the
air.
That's almost three times Yellowstone.
Its grim aftermath was a global cataclysm, including a global cold spell and persistent
drought.
One theory holds that Toba brought the human species perilously close to extinction.
What causes a catastrophe on this scale?
The answer takes us back to the birth of our sun, around five billion years ago.
It began in a swirl of debris, likely drawn together by shock waves from a stellar explosion.
Amid the chaos of the early solar system, gravity drew clumps of rock and dust and gas
together.
A fiery young planet formed, molten at first.
Millions of years passed.
Earth's surface gradually cooled, but its interior remained hot.
Add to that, heat generated deep within the planet by the radioactive decay of uranium,
thorium, and potasium.
To this day, heat energy is rising steadily from Earth's interior, a vivid reminder of
the fires that burn inside it.
The heat makes its way to the surface through a vast middle region called the mantle.
It punches through where Earth's crust is thinnest, in the middle of oceans.
That causes massive plates that line the surface of the planet to push apart, often flooding
the ocean floor with lava.
These oceanic plates collide with thicker continental plates.
That drives them down into the Earth, along with volcanism's secret ingredient: water.
Some rocks, when mixed with water, melt more readily.
They form a reservoir of magma deep below ground.
As more magma enters the reservoir, the pressure increases.
That forces magma up to the surface, and a volcano erupts.
A supervolcano like Toba or Yellowstone begins with a much larger reservoir of magma.
A recent study showed that the larger it gets, the more bouyant the magma becomes amid the
solid crustal rocks that surround it.
Over time this bouyant reservoir pushes up on the terrain above it.
The rock above the magma begins to break.
Channels, or dykes, form, to release the rising magma.
The volcano does not so much erupt, as it explodes.
The land collapses onto the magma, helping to propel it up and out.
The thermal features that dot Yellowstone are
small in scale, yet they too are fueled by an immense dome of magma deep underground.
By tracking the pattern of seismic waves from small earthquakes, scientists have been able
to follow it down to its source.
A kilometer below, surface water enters layers of heated rocks, then shoots back to the surface
in hot springs and geysers.
Deeper still, ten kilometers down, they've located the upper reaches of an immense reservoir
of magma.
It measures over a hundred kilometers wide and four hundred kilometers deep.
Scientists now believe it's partly the result of the the Pacific Ocean Plate diving below
North America,mand partly the product of a hot spot.
It's similar to a deep plume of magma that fuels Hawaii's volcanoes.
Over the last 16 million years, as the continent of North America has moved, inch by inch,
over the Yellowstone hot spot, the volcano has reawakened time and again.
The next to the last time, it ejected 5,000 cubic kilometers of material into the atmosphere,
almost twice as much as Toba.
Toba is known to have erupted at least three times in the last one million years.
There are signs that it's gearing up for another.
Some parts of the caldera, including a large island in the middle called Samosir, have
risen due to a refilling of the magma chamber.
Indonesian scientists recently reported they have detected its presence, starting at a
depth of 20 to 100 kilometers down.
The volcano is not active now.
But it's in one of the most geologically active regions in the world, including the nearby
Sumatran fault and the Sumatran Subduction Zone.
This region is known for major earthquakes and a string of volcanoes, including Krakatoa
and Tambora.
If or when Toba does erupt again, it still won't hold a candle to Earth's greatest eruptions.
Roll back the geological clock, to a time around 65 million years ago.
A giant asteroid slammed into the Earth.
It wreaked havoc on the climate and may have led to the extinction of the dinosaurs.
The impact coincided with another type of catastrophe.
That was a time when today's continents were taking shape.
The Himalayan mountains were beginning to rise up.
And India had not yet crashed into Asia.
In central India, one of the largest volcanic structures on Earth made its presence felt.
From the so-called Deccan Traps, the Earth literally spilled its guts.
Over a period lasting perhaps 30,000 years, 500,000 cubic kilometers of lava flooded onto
the Indian landscape.
The Deccan traps eruption was about 500 times larger than the last Yellowstone eruption.
An even larger, more destructive event occurred around 235 million years ago in what's now
Russia.
Back then, all of Earth's land masses were joined together in a supercontinent known
as Pangea.
In a period known as the Permian, amphibians and early reptiles flourished.
Insects were everywhere.
Fern plants, dominant for eons, were beginning to give way to conifers and palms.
In the oceans, amid vibrant coral reefs, invertebrates and fish inhabited the open water.
Then, in the geological blink of an eye, it was over.
For a period lasting up to ten million years, countless small eruptions generated several
thousand times more lava than Yellowstone, spreading over an area the size of Western
Europe.
What it brought was not volcanic winter, but rather hell on Earth.
The atmosphere became choked with carbon dioxide and methane gas.
The Earth belched deadly toxins, including high levels of mercury.
Temperatures around the world soared.
The oceans turned acidic, their waters depleted of oxygen.
By the time it was over, up to 70 percent of all species on land, and 90% of marine
species, had disappeared.
Ecosystems around the planet collapsed in what scientists call the "great dying."
And that was not even the largest volcanic eruption in Earth's history.
For now, that honor goes to an undersea eruption that began 125,000 years ago, creating a plateau
thirty kilometers thick called Ontong Java.
It released about 100 million cubic kilometers of magma.
Scientists believe large eruptions like Ontong Java or Siberian Traps occur where broad regions
of magma, called large igneous provinces, push toward the surface.
The Earth is pocked with dozens of them.
They are spread out across all the continents and oceans.
Thankfully, these regions have erupted only very rarely in Earth's history.
Super eruptions on the scale of Yellowstone and Toba, linked to the movement of crustal
plates, are more frequent, perhaps every 100,000 years or so.
Because so little is known about what triggers them, there's no telling when or where the
next one will occur.
Are we due?
Scientists at Yellowstone are watching for early signs: earthquakes, rising heat, the
restless stirrings of a planet under pressure.
Someday, somewhere, Earth will once again vent its rage.
When it does, we can be sure that it will change our world forever.