Nova (1974–…): Season 44, Episode 23 - Killer Volcanoes - full transcript

Volcanologists search for an elusive volcanic mega-eruption that plunged the medieval earth into a deep freeze. Investigate the geologic evidence from Greenland all the way to Antarctica to identify the 750-year-old culprit.

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Our planet is capable of
unleashing extreme chaos.

Volcanoes, earthquakes,
hurricanes, and floods

can cause untold devastation.

We may think we've seen

the worst Mother Nature can
throw at us,

but scientists struggling
to understand these disasters

are discovering evidence
that even more extreme events

have struck in the past.

So this is about 13 times

more powerful
than the Pompeii eruption.

They're uncovering clues



that the worst
catastrophes in history

could strike again.

Nearly 1,000 years ago, a
disaster shook the world.

This is one of
the largest eruptions

in the last 10,000 years.

A volcano so powerful it
chilled the entire planet.

But where was it?

No one knew the source
of the eruption.

The clues are here, buried and
hidden all around the world.

Now, scientists come together

to scour our volatile Earth,
to solve the mystery

of killer volcanoes.

Right now, on NOVA.

Of all the forces of nature,



volcanoes are among
the most dangerous.

They have the power

to kill millions and disrupt
the fabric of modern life.

Volcanoes can have
a global impact.

Today, there are more than 1,500

active volcanoes on Earth.

About 50 erupt every year.

Many are well known,
like Vesuvius in Italy,

and Mount St. Helens
in Washington State.

But could there be
other slumbering giants

that we have never heard of?

Volcanoes that were once

even more powerful
and destructive

than today's monsters?

That's what a series of clues
is suggesting.

Scientists working
across the world

have begun to find evidence
of a cataclysmic event,

a mysterious eruption
that could have been

one of the largest
in human history.

And the trail starts
in a very unexpected place.

Here, in the heart of London,

archaeologists
uncover a surprise.

While excavating
a medieval cemetery,

they happened upon
a series of mass graves

on the edges
of the burial ground.

Over 4,000
men, women and children,

packed into large pits.

The cause of death
was not obvious.

So what killed so many people,

and why were they all
buried together?

When we find mass burial pits,

we know that
there's been a lot of people

dying very quickly, and
something has gone very wrong.

As a first step
to identifying the killer,

archaeologist Don Walker
and his team conducted

radiocarbon tests, to find out
how long ago they died.

The hope was that
they could tie their deaths

to some historical event.

But what they found
merely deepened the mystery.

The victims all died
around 1250 in the Common Era.

That ruled out

one of the most notorious
mass killers of the past,

the Black Death,
which ravaged Europe

about a century later, in 1348.

So what could have caused
this mass killing?

Don Walker heads
to the British Library

to consult ancient historical
records from the period.

This manuscript
is a history of England.

Over 750 years old,
it was written in Latin

by a monk named Matthew Paris.

Among these chronicles,
one account stands out...

A description of bitterly
cold weather around London

in the spring and
early summer of 1258

that kills crops and livestock

and leads to a deadly famine.

It says owing to
the scarcity of wheat,

a large number
of poor people died,

and dead bodies
were found in all directions,

swollen and livid.

Then Walker discovers

a description that
seems to match the discovery

of the mass graves.

When several corpses were found,

large and spacious holes
were dug in the cemeteries,

and a great many bodies
were laid in them together.

And of course, as soon as I
saw that, I got very excited,

because it's exactly
the kind of thing that we found

at St. Mary Spital, where they
were digging these huge pits.

According to this text,

the famine killed
over 15,000 people in London.

That's 30% of the city's
population at the time.

You're talking about something

that was perhaps nearly as
deadly as the Black Death.

And possibly as widespread too.

Other sources reveal
the far-reaching impact

of the extreme weather and its
disastrous effect on crops.

There are various records
from this period...

1258, 1259, 1260,

in various parts of Europe
and as far as Japan,

that do attest
to extreme impacts

in terms of famine,
in particular.

Something devastating

was plunging much
of the Northern Hemisphere

into a pattern of bitter winters

and summers blighted
by torrential rain.

We thought perhaps
this was something to do

with some catastrophic event.

Only one type
of natural disaster

could have such a widespread
impact on the climate...

A massive volcanic eruption.

But which volcano
was the culprit?

The closest volcanoes are a
thousand miles away in Iceland.

In 2010, when a volcano
known as Eyja erupted,

it sent an ash cloud over Europe

that disrupted air travel
for weeks,

stranding people
all over the world.

And historical records
reveal that in 1783,

eruptions from the Laki volcano

caused mass deaths
across Europe.

It seems like
an Icelandic volcano

could be to blame for the
mysterious 13th century event,

but Walker came across
another possibility.

He became intrigued by one of
the most massive eruptions

in recorded history,

even though it occurred
just 200 years ago

and was located
much farther away...

Mount Tambora in Indonesia.

In April 1815,
eyewitness accounts record

that Mount Tambora
erupted explosively.

And this is one of
the largest eruptions

of the last 10,000 years.

It's estimated
over 60,000 people died

in the shadow of this volcano.

But the eruption had an
even more far-reaching impact.

In northern Europe
and North America,

the year after the eruption,
1816, is known as

the year without a summer.

In New York State,
it snowed in June.

In Europe, cold weather led to
the worst famine for a century.

The climate change

caused agricultural failures,
poor harvests,

it pushed up grain prices,

with many people perishing
from malnourishment.

So perhaps another
powerful eruption

could have caused the year
without a summer in 1258.

We began to think that perhaps
this might be something to do

with what had happened
back in the 13th century.

Perhaps this was
why the people starved.

But to pinpoint the location

of the mysterious volcano,
they needed to know more

about its size
and type of eruption.

They look at one of
the largest volcanic events

in recent memory...

the 1991 eruption of Mount
Pinatubo in the Philippines.

Unlike volcanoes that erupt
by pouring out rivers

of molten lava
over a long period of time,

Pinatubo erupted
suddenly and violently...

...when water and gases
trapped inside the magma

exploded with tremendous force,

shattering the rock into
millions of tiny particles

and sending them
high into the atmosphere.

Explosive eruptions like this
are the most dangerous of all.

Pinatubo killed
847 people locally,

and left over 200,000 homeless.

But as with the other
big Indonesian volcano,

Mount Tambora, this eruption
also had far-reaching effects.

NASA's satellites were able
to monitor the eruption.

Pinatubo blasted out one
cubic mile of superheated ash,

but it also ejected
hundreds of millions of tons

of volcanic gases in a
plume 22 miles high.

The ash and the gases

are dispersed through
the atmosphere by the wind,

and they can travel
thousands of kilometers,

tens of thousands of kilometers.

But unlike heavy ash

that soon falls
out of the atmosphere,

the lightweight gases
persist for much longer.

The most impactful gases
are the sulphur-rich gases.

And those gases will form little
droplets of sulphuric acid

in a large cloud.

The tiny drops of sulphuric acid
are called aerosols.

And in a large cloud,
high in the upper atmosphere,

these aerosols caused enough
sunlight to reflect

out into space
to cool the planet.

The satellite data revealed
that this sulphuric acid mist

had a much more dramatic impact
than the ash.

It blocked enough sunlight
to cool the entire planet

by one degree Fahrenheit
for two years.

That doesn't sound very much,
but it actually masks

much stronger
regional variations.

And that translates into
real impact on the ground

in terms of crop yields.

In 1258, the temperature drop
was much greater

than caused by Pinatubo.

This suggests that whatever
triggered this medieval disaster

could have been much bigger.

That indicated that a big event
occurred somewhere in the world.

But there was no record of
a massive volcanic eruption.

For volcanologists,

it was
the biggest mystery for us.

So where could
the culprit volcano have been?

And after more than 750 years,
could this killer volcano

be found?

It seemed the trail
had gone cold,

until a clue appeared,
frozen in the polar ice.

About 1,000 miles
from the North Pole...

...researchers for the
Greenland Ice Sheet Project

are taking core samples
from deep in the ice.

This ice sheet was built
layer by layer

as snowfall accumulated
over 130,000 years.

The deeper into the ice
the scientists drill,

the farther back in time
they can look.

The samples arrive for analysis
at the Desert Research Institute

in Nevada.

Geochemist Nelia Dunbar
and glaciologist Joe McConnell

are preparing to analyze
an Arctic ice core sample

that contains snowfall
from the mid 13th century.

The core comes from 1,000 feet
below the surface

of the ice sheet.

They will be looking
for sulphuric acid...

Evidence of an intense eruption.

If there were
a big volcanic eruption

that produced a lot of sulphur,

that sulphur should be
preserved in this ice.

And that's what
we're interested in studying.

Where is this from,
and what's the age of it?

So this piece is
from around 1250, 1255 AD.

This represents
about three years.

So this is roughly one year,

roughly one year,
and roughly one year.

These ice cores hold
an incredible record

of past climate.

In between the snow crystals are
little pockets of atmosphere

that are little time capsules
that represent

the composition
of the atmosphere

at the time the snow fell.

Over time, more snow
will fall on the ice sheet,

and that record is locked in.

Up to the right
and then up to the top.

But to unlock the record,

scientists have to destroy it
inch by inch.

Okay, so now we're ready
to start the analysis.

Okay.

As each layer of ice melts down,

the melt water passes through
a mass spectrometer.

It's like a time machine

that reads out the chemicals

that were in the atmosphere
hundreds of years ago.

The results start
to come through.

And the team immediately
sees a telltale spike.

So we're seeing the responses

come up on all the various
instruments right now.

So this would be 1258,
and you can see the acid now

has just skyrocketed, a
huge increase in sulphur.

So it's certainly
pointing to volcanism.

Okay, so that must have been
a really big volcanic event.

Yeah, absolutely huge.

The sulphur locked inside

the 1258 ice layer
tells the story

of a powerful volcanic eruption.

And though the sulphur
was washed out of the atmosphere

in rain and snow in 1258,

the eruption itself likely
occurred the year before.

Now, keep in mind

that it takes a while
for the sulphur to make it

from the volcano
through the atmosphere

and be deposited
on the ice sheet.

Mm-hmm.

And so this event,
it probably occurred in maybe

mid to late 1257.

And the amount of sulphur
ejected by this eruption

was vast by comparison
with that produced

by the other known eruptions
captured in the ice cores.

Here's the 1257 of that
that we just measured again

in this new ice core.

We can see that it's huge.

When you compare it to Tambora,
here in 1815, it's, you know,

something like
more than twice as big.

So this is a really,
really big event.

And at least in this composite
it's the biggest event

of the last 2,000 years,
very clearly.

So this eruption
seems to have been large enough

to account for the
freak climate disaster

across the Northern Hemisphere
in 1258,

including London's
deadly famine.

It was hard to really pin down
one event and say,

"This was the result
of a volcanic eruption."

But I think in this case
the evidence is quite strong.

You can imagine
living in medieval London.

You know that you haven't
got enough food to live,

your crops are failing,
the weather's very bad,

but you'd have no idea the true
cause of what was going on.

The true cause

was that somewhere
on the planet, in 1257,

a volcano exploded
and blasted its contents,

including poisonous gas and ash,
high into the atmosphere,

where it dimmed the sun
for months, if not years.

But where was this killer?

The mystery that remains
is what was the volcano

that was responsible for
this big volcanic eruption?

More than 1,500 volcanoes

have been active
in the last 10,000 years,

so pinpointing which
of these caused

such a massive disruption
in 1258 is a huge challenge.

The first place to look
is a string of volcanoes

known as the
Pacific Ring of Fire.

The continents we live on

ride atop giant tectonic plates
made of rock.

Where plates collide
or slide under each other

gives rise to volcanoes,

making this one of the most
geologically active regions

of the world.

But the Ring of Fire
extends for thousands of miles.

How can scientists work out
which volcano is the culprit?

In her lab at the
New Mexico Bureau of Geology,

Nelia Dunbar examines
some distinctively shaped

mineral particles lodged
in a section of ice

from a different
Greenland ice core.

The particles also date to 1258,

when the sulphur concentrations
are highest.

Could these particles
be possible clues

to the volcano's identity?

At 50,000 times magnification,

it's clear that
the mineral particles

are actually microscopic
pieces of volcanic ash.

These particles are smaller
than a human hair.

The ash particles

are fragments
of shattered pumice,

produced when magma cools
rapidly during an eruption.

And their chemical composition

is unique to each
volcanic eruption.

Just like a human fingerprint
allows a suspect

to be identified, the chemical
composition of an ash layer

allows the source volcano
to be identified.

This unique signature didn't
match any known volcano.

But it did show up
in one other surprising place...

...at the exact opposite
end of the world,

in ice cores
taken from the South Pole.

These cores also contained
a significant spike

in sulphuric acid,

corresponding to the eruption
in 1257.

This means that
the monster darkened not only

the Northern Hemisphere, but
the Southern Hemisphere as well,

smothering the entire world
in a blanket of sulphuric acid.

Climatologist Michael Mills

believes the size
of this global cloud

can help pinpoint the place
where the volcano erupted.

He uses satellite data

to map how clouds of sulphuric
acid aerosols

disperse around the world.

Let's look at what happens
when you have an eruption

in the Northern Hemisphere.

In 2008, we had
several eruptions,

and the aerosol stays
in the Northern Hemisphere.

Now look at what happens

when you have an eruption
in the Southern Hemisphere.

The aerosol spreads,
and will remain

in the Southern Hemisphere.

But how could an aerosol cloud
reach both hemispheres?

For that, an eruption has to
occur within a narrow band

around the middle of the globe.

This is Pinatubo
in June of 1991,

in the Philippines.

It starts spreading
throughout the tropics,

and from there, it spreads

into the Northern Hemisphere
and to the Southern Hemisphere.

Within a year
after the eruption,

the aerosol has covered the
globe from pole to pole,

affecting temperatures globally.

The mystery eruption of 1257

also spread a cloud of
sulphuric acid over both poles.

So it too must have erupted
near the equator.

But that still leaves over 700
possible volcanoes as suspects,

like Mount Tambora, that led
to the year without a summer,

Krakatoa, that also erupted
in Indonesia in 1883,

and El Chichon in Mexico,
that erupted in 1982.

Any one of hundreds
of tropical volcanoes

could have caused
thousands of deaths

on the other side of the planet,
but which one,

and could it strike again?

It's still a needle
in a haystack

to find the one volcano,
the one eruption

that triggered all of this,
because there are

so many volcanoes, even if you
narrow it down to the tropics,

where do you start?

It seemed an impossible mystery
to solve.

But then a French geographer

named Franck Lavigne
decided to take it on.

For me it looks

a bit strange that nobody found
this eruption.

So I decided
to take up the challenge.

He approaches it as a detective.

Trying to find the identity
of this mystery volcano

was like a crime scene.

So we needed to investigate,

to look for culprits,
to look for clues.

Volcanologist
Jean-Christophe Komorowski

joins the investigation.

It's a very large eruption.

It's an unknown eruption,
so it has to be in a country

where there are
many, many volcanoes,

most of them perhaps
have not been studied.

The team focuses on one
particularly active region

of the Pacific Ring of Fire...

Indonesia, home of
the once deadly Mount Tambora,

that last erupted in 1815.

With 129 active volcanoes spread
over 3,000 miles,

Indonesia is the most volcanic
country in the tropics.

It is also one of the most
unstudied and mysterious.

Indonesia has

the second largest number of
active volcanoes in the world.

Indonesia marks the place

where two giant
tectonic plates collide.

Here, one plate
dives under the other

in a process called subduction.

At depth,
the diving plate releases water,

which lowers the melting point
of the hot rock above.

The rock melts, forming giant
bubbles of magma that rise up,

forcing their way
through the Earth's crust,

until the magma erupts
at the surface.

Today, the most dangerous
Indonesian volcano

is Mount Merapi
on the island of Java.

This volcano erupts explosively
every few years...

...threatening hundreds
of thousands of people

who live in its shadow.

Merapi volcano is considered

to be one of the most active
volcanoes in the world.

The last major
eruption was in 2010.

400,000 people evacuated.

Even so, more than 200 died
in the avalanches

of superheated ash and rock,

called pyroclastic flows.

20,000 were left without homes.

The ash produced by Merapi

does not match
the chemical fingerprint

of the ash in the ice cores.

But understanding the forces
that make this volcano

so dangerous sheds light on all
of Indonesia's active volcanoes.

So which one exploded so
catastrophically in 1257?

Geographer Lavigne

hunts through satellite images
for large volcanic craters

and other telltale signs.

And one of these clues
is a large volume of pumice

all around the volcano.

Pumice, a rough textured rock,
is solidified magma,

blasted out during
explosive eruptions.

When you suddenly depressurize

and cool magma that was
very rich in gas,

it forms this very lightweight,

foamy rock, which is pumice.

It can be a deadly material.

When Mount Vesuvius erupted
in Italy in 79 the Common Era,

it entombed the town
and the people of Pompeii

in layers of pumice
16 feet deep.

Throughout Indonesia today,
pumice mines dig out

this volcanic material,
primarily for use

in the construction industry.

And the scars left by the
quarrying work are so extensive

that they're visible from space,
making it easy for scientists

to pinpoint locations
for further investigation.

Journeying to Indonesia,

Lavigne works with partners
from the government's

geological agency
and Indonesian universities.

They visit several volcanoes,
with no success.

At each site, the pumice
is compacted and hard,

likely too ancient
to have been created

during the 1257 eruption.

It seemed older

than we had predicted, so older
than the 13th century.

Then the team
sees something intriguing

in the satellite images,
and decides to narrow its search

to the island of Lombok,
just east of Bali.

This island is
quite a big island,

with a very big crater.

Stretching four miles across

and over two and a half
thousand feet deep,

this giant crater
is called a caldera.

It's what remains of a volcanic
system known as Mount Rinjani.

When you have a very large
explosive eruption,

you're left at the end of the
eruption with a huge hole.

To the team's expert eyes,
it looks like there were

not one, but two giant volcanic
peaks here in the past...

Mount Rinjani itself,
and a second peak that once rose

above the main part
of the caldera.

Today, inside this caldera
is now a small volcanic cone...

Mount Barujari.

Surrounded by a rainwater lake,

Mount Barujari is the part
of the volcanic system

that is still active.

In 2015 and 2016,

this small cone erupted
with enough force

to send plumes of ash thousands
of feet into the atmosphere,

disrupting international flights
in the area.

It's far too small to be the
source of the mystery eruption,

but the caldera it sits in
is large enough

to have been created during
a much more powerful eruption.

And all around the
Mount Rinjani volcanic system

are pumice quarries.

Everywhere in the island

you can find a pumice quarry.

Could the pumice in these
quarries be dated

to help in their investigation?

The team travels to Lombok.

And the hunt starts in the
shadow of Mount Rinjani...

...a peak that soars
12,000 feet high.

On the island, they join forces
with more Indonesian experts.

They head for the quarries

identified in
the satellite images.

And as soon as they arrive, they
discover something remarkable.

The volcanic pumice deposits
are at least 120 feet deep.

Here we are, looking at the
huge volcanic deposit.

And that's very rare, to
find so thick deposit

very far away from
the summit of the volcano.

Pompeii, just over five miles

from the erupting
Mount Vesuvius, was buried

under 16 feet of pumice.

Here, the deposits of pumice
and ash are at least

six times thicker,
and they are much farther away

from Mount Rinjani than Pompeii
was from Mount Vesuvius.

It's a sign of a giant eruption.

You're dealing with
a very massive eruption.

Much larger than
the Pompeii eruption,

and probably also much larger
than the Pinatubo eruption

in 1991.

And it looks to them
as though the ash and pumice

flowed down from the volcano
in vast avalanches.

You can see it's very rich
in finer material.

It's not pumice falling
from a column, raining down.

It's an avalanche
of incandescent,

hot volcanic rocks
mixed with gases.

My first impression,

when I saw such a huge deposit,

was that we have here
a very serious candidate

for the mystery eruption.

But is all this pumice

from the mystery eruption
of 1257?

To confirm that this eruption
is the 1257 eruption,

we need to try to find charcoal,
wood logs that were burned

by this eruption, carried by
the pyroclastic flow,

and settling here,
and we need to date those.

If they can find burned wood,
they can radiocarbon-date it,

since, unlike pumice,
wood contains carbon

absorbed from the atmosphere.

And by taking samples
of the pumice itself,

the team hopes
to compare its chemistry

with the fragments of volcanic
ash from the polar ice cores.

But Lavigne still needs
more evidence, so he decides

to investigate Lombok's past

to see if he can find records
of historic eruptions.

Under lock and key in the museum

of Lombok's capital city,
Mataram,

is an original text, written
on dried palm leaves,

in an old Javanese script.

Called the Babad Lombok,

this text is a rare account
of Lombok's history.

It chronicles the story

of Lombok, from prehistoric
times to historic times.

And hidden in this document

is a remarkable account
that historians have dated

to the 13th century.

Mount Rinjani avalanched,

and Mount Samalas collapsed.

Rocks flooded down in rows.

It describes a huge
volcanic eruption

that occurred in Lombok.

Lavigne is familiar
with Mount Rinjani,

mentioned in the text, but
not the name of the volcano

that's described as collapsing...
Mount Samalas.

This description
is absolutely fantastic,

because it mentions the name of
a new volcano, Mount Samalas.

I never heard about this before.

This remarkable discovery
raises a new question...

Could the giant caldera
the team saw on satellite images

belong to the unknown
Mount Samalas?

The text also reveals the scale
of the human catastrophe.

The text in the Babad

says these flows destroyed the
seat of the kingdom, Pamatan.

All houses were destroyed
and swept away,

floating on the sea,
and many people die.

There is a strong possibility
of the remains of this capital

still lie preserved beneath
the pumice, just like Pompeii.

The text is a tantalizing clue,

but could it just be a myth?

It made this volcano our chief
suspect in our investigations,

but to confirm it was the one,
we needed scientific proof.

So the team decides
to mount an expedition.

To trek into the mountains
and hunt for hard evidence

at an altitude of 9,000 feet.

From up here, the team can
assess the landscape and geology

in a way that's impossible
from satellite images alone.

Exposed in the cliffs
are geological layers

that allow
Jean-Christophe Komorowski

to work out the sequence
of events that led

to what we see today...

...the giant caldera.

These cliffs are the remains
of a very massive volcano.

And towering over the east side,

the remains of Mount Rinjani.

You can see the slopes

of Mount Rinjani volcano
rising to 3,700 meters.

And it was much higher before.

The scars in the cliffs

suggest to Komorowski
that half of Mount Rinjani

avalanched into the caldera
after it formed.

The formation
of the Samalas caldera

destabilized Mount Rinjani,

which collapsed
into the caldera,

and this formed this
massive sheer cliff here.

To the experts, it looks like
Mount Samalas once stood

next to Mount Rinjani,

just as the ancient text
describes.

In fact, the latest
research found that there was

a volcanic mountain
called Mount Samalas,

which in the end is different
than Mount Rinjani.

By extending the existing slopes
of the volcano,

experts have reconstructed
what Mount Samalas looked like.

Imagine that,
before the eruption

you had a huge conical volcano

rising 1.6 kilometer above
the rim of this giant hole.

That's an extra mile in height
of volcanic mountain.

So how did several cubic miles
of rock disappear

and leave an enormous caldera
in its place?

It all begins
with a giant eruption.

And in order to form a caldera,

you have to have first a very
massive explosive eruption.

In a magma chamber

far beneath the volcano,
the pressure rises,

and finally cracks open
the rock above.

Magma blasts upwards.

As this chamber empties,
it becomes unstable.

This destabilizes
the whole volcano on top.

The roof of this
partially empty chamber

now cracks under the weight.

And it collapses.

The entire top of the volcano
caves in.

Billions of tons of rock
disappear as it falls

thousands of feet down
into the magma chamber below,

forming a giant crater above...

...the enormous caldera.

But that's not the end.

As the volcano
collapses on itself,

it forms a massive
explosive eruption,

producing giant
pyroclastic flows

that sweep down
the flanks of the volcano.

This catastrophic event

explains the depth
of the pumice deposits

in the quarries,

and closely aligns
with the ancient story

in the Babad Lombok.

It gives a name
to the volcano that existed

at the beginning
of the eruption, Mount Samalas,

and it describes how Mount
Samalas collapsed in on itself.

Altogether, the description
in the Babad matches remarkably

what we have found
in our field investigations.

We now know that
Babad was not a legend,

but eyewitness accounts.

If the long-forgotten
Mount Samalas

was the source of the giant
eruption on Lombok,

as the evidence suggests,
could it also be

the mystery eruption of 1257?

To answer that definitively,

the team still needs
more forensic evidence.

It's really critical
to get on the ground

to look at the actual
rocks themselves.

They take samples

of pumice and ash
from over 100 different sites

across Lombok
and on neighboring islands.

They conduct geophysical surveys

to measure the depth
of the volcanic deposits

still buried beneath the ground.

And they investigate whether

gases from this eruption
could have reached high enough

into the upper atmosphere
to spread globally.

To assess the scale
of the eruption,

we looked at these
pumice fragments

that were ejected
by the eruption column.

And the idea is that
the further away

you find big fragments,
it means that these fragments

were ejected with
a lot of energy...

...and that the eruption column

reached very high
in the atmosphere.

In this case, pumice fragments
two inches across

were found 29 miles away on
the nearby island of Sumbawa,

allowing the team to calculate
that the pumice likely ascended

nearly 27 miles high...
More than ten miles higher

than the Mount St. Helens
eruption of 1980.

This is one of
the highest column heights

for explosive eruptions
in the last 10,000 years.

The Mount Samalas eruption

was certainly massive enough
to cool the entire world.

But can scientific tests prove
that the pumice

was from the mystery 1257
eruption?

In Paris, French volcanologist
Celine Vidal goes through

the samples taken
from Indonesia.

First, she selects
pieces of carbonized wood

found inside the pumice deposits
for radiocarbon dating.

We analyzed 20 pieces
of carbonized wood

from sites all across
the volcano,

and the carbon 14 dating
told us that the eruption

dated to the second half
of the 13th century.

All the results were consistent

with the mystery eruption.

The dates are in range,

but there is one final test.

Will the chemical fingerprint
of this eruption

match the fingerprint
in the polar ice cores?

At high magnification,

Vidal compares
the volcanic ash fragments,

one from the Antarctic ice core
from 1257,

and one from the pumice deposits
on Lombok.

You can see that the surfaces

of the two different
particles of ash

have the same texture, and that
their edges are very sharp.

They appear very similar.

But how closely do their
chemical fingerprints match?

I add now the chemical
composition of the ash

from Samalas here in blue,

and one sees that the peaks
correspond perfectly.

They are comparable
to more than 99%,

and that is really excellent.

This allows us to conclude that
they are from the same origin.

Now there is finally enough
evidence to remove all doubt...

The mystery killer volcano
is here on Lombok,

Mount Samalas, once known
and since forgotten.

The team was very excited
by the result.

The source of the 1257 eruption
has been a mystery for 30 years,

so we were quite excited
when we were able to prove

that Mount Samalas
erupted in 1257.

The mystery of the massive spike
of sulphuric acid

in the polar ice cores,
the global volcanic winter

caused by a cloud of aerosols
that blocked the sun,

and likely, the thousands
of people killed in London

in a catastrophic famine,
all have been answered.

By combining these discoveries

with the investigation
on the volcano,

the team can now unpack
the eruption blow by blow.

The 1257 eruption
started with a very explosive,

violent eruption
from Mount Samalas.

At its peak,
the eruption blasted out

one million tons
of material a second.

And that produced
a very tall eruption column

of ash and gases and pumice,

rising 43 kilometers
in elevation.

Nearly four cubic miles
of pumice and ash

rise four times higher
than the operational altitude

of a passenger jet.

While the gases remain aloft,
most of the pumice and ash

then falls back to Earth.

And it produced a rain of pumice
over a very vast area.

It covers an area at least
450 miles across.

During the final collapse
of the volcano,

six cubic miles
of pumice and ash

form giant pyroclastic flows.

Racing down, they reach speeds
of over 125 miles an hour,

at temperatures
of 1,500 degrees Fahrenheit.

They covered the entire
landscape of Lombok

with thicknesses
of five to 50 meters,

reaching the sea in many places.

But even as the dust
settles on Lombok,

the vast volcanic cloud starts
to envelop the entire world,

even as far away
from the eruption

as North America and Europe.

The fact that we have
so many thousands of people

buried in these mass pits
as a result

of this volcanic eruption

just shows us what
a global event it was.

This was possibly the most
massive volcanic eruption

in recorded history.

And it raises
a troubling question.

Could another eruption of this
magnitude happen again?

It's been 750 years since the
giant eruption of Mount Samalas,

yet inside its vast caldera,
eruptions from Mount Barujari

reveal that the volcanic system
is still active.

Two and a half thousand feet
below the caldera rim,

Komorowski rejoins the team
of Indonesian volcanologists,

monitoring the active heart

of the Samalas/Rinjani
volcanic complex.

Using thermal imagery
and making a risky trek

to collect lava
from the latest eruptions,

the Indonesian volcanologists

are gaining an ever
more accurate picture

of the volcano's activity
level today.

And the most telling clue
to the volcano's activity

is not the cone itself,

but the rainwater lake
that surrounds it.

Volcanologist
Devy Kamil Syahbana

measures the water temperature.

At an altitude 6,500 feet,
more than a mile high,

this lake should
have a temperature

of about 60 degrees Fahrenheit,
or 15 degrees Celsius.

But here we have, like,
20 to 22 degrees Celsius,

which is much hotter
than a normal lake,

which indicates a very strong
magmatic activity

beneath the caldera.

The eruption of 1257

likely left a lot of magma
behind, inside this chamber.

The volcano is still
under pressure,

and it is still unstable.

The volcano remains active,

but their analysis tells them

that there is
insufficient pressure

to power a 1257-scale eruption.

But what about other volcanoes?

According to the ice core
record, there have been at least

seven explosive eruptions
on the scale of Pinatubo

near the equator since 1257.

It will happen again.

The worry is, no one knows when.

If another major explosive
eruption were to happen

today in the equatorial region,

it would have
devastating consequences.

There'll be huge disruption
to global aviation.

The economic impact would
be really catastrophic.

These massive volcanic events

really impact
on people globally.

It affects their climate,

food source, causes famine,

and can cause catastrophic
numbers of deaths.

750 years ago,

an eruption on a small island
in Indonesia

destroyed lives
on the other side of the world,

reminding us again of the power
of our volatile Earth.

This NOVA program
is available on DVD.

NOVA is also available
for download on iTunes.