All language subtitles for NOVA.S45E11.Volatile.Earth.Volcano.on.the.Brink.1080p.AMZN.WEB-DL.DDP.2.0.H.264-GNOME_track3_[eng]

In the heart of Africa

are two of the world's
most dangerous volcanoes.

Within their craters,
molten lava steams and boils.

Over centuries

these volcanoes have erupted
many times,

but when will they erupt again?

It's a crucial question,

and no one knows the answer

because these are among
the least-studied volcanoes

in the world.

Now an international team
of scientists

has come to investigate
these giants,

to predict future eruptions
and save lives.

Everything we do to understand

this volcano is very important
to avoid another disaster.

Today,

they're flying
to a volcano called Nyamuragira

in a region rife
with dangerous militias.

After many active years,

this volcano
has stopped erupting.

The fire in its crater
appears to be gone.

We need to collect some really
critical data up there

to understand
what might happen in the future.

Will Nyamuragira erupt again?

And if so, when?

The people who live here
are at risk.

Can scientists find a way
to protect them

before time runs out?

Right now,

I just want to get things set up
and going,

so we can just get
as much as possible

in this really short time
that we have here.

Can they solve the mystery

of "Volcano on the Brink"?

Right now, on "NOVA."

Right now, on "NOVA."

In a remote
region of central Africa

lies one of the most active
yet least explored volcanoes

on the planet:

Nyamuragira,

as spectacular
as it is mysterious.

The volcano sits
on the eastern border

of the Democratic Republic
of Congo, the DRC,

near the shores
of the vast Lake Kivu.

Fewer than 20 miles
from the volcano

is the town of Sake.

Its residents
are all too familiar

with the threat
of its frequent eruptions.

Market traders Terese Kalume
and Mama Noya

have spent their entire lives
here

and witnessed the effects
for themselves.

Nyamuragira eruptions
blanket large areas of farmland

in scalding-hot, choking ash,

destroying crops,
killing livestock,

and bringing famine.

At the moment,
there is just such a break.

It's been five years
since the last major eruption.

Has the volcano gone extinct,

or will it erupt again,
more deadly than before?

It's this question

that an international group
of scientists

has come to investigate.

To do that, they have to be
transported to the volcano

by a United Nations
peacekeeping team.

For British geologist
Chris Jackson,

it's a field trip like no other.

It's
actually in a fairly dangerous

part of the the area,

so the only way to get there is

with a military helicopter.

My heart's racing
just at the thought

of getting on that helicopter.

Few people
have visited Nyamuragira--

for good reason.

This region of the DRC
was the center

of one of the bloodiest wars
of modern times.

Fueled by
a long colonial history,

vast mineral wealth,
political tensions,

and international pressures,

millions were killed
and injured.

Although the war
is officially over,

widespread unrest continues.

Violent militia and rebel groups
are operating in nearby forests,

so the helicopter flies fast
at treetop level

to stay out of their gun sights.

Even at this speed,

the helicopter provides
a great vantage point

to see one
of the most volcanic places

on earth.

American volcanologist
Kayla Iacovino

has studied volcanoes
across the planet,

but the volcanism here

is on a scale
she's never experienced.

I thought I knew

what this landscape
was going to look like,

but there's really
way more volcanoes,

way more melt here
than I expected.

It's... the amount of
magma production in this region

is insane.

As they reach Nyamuragira,

they can see
it's a giant shield volcano,

so called
because successive lava flows

have spread widely
across the landscape,

giving its surface
a sloping, shield-like shape.

The volcano rises
to over 10,000 feet,

surrounded by old lava flows

that blanket
almost 600 square miles.

At the summit,

the main caldera created
by previous eruptions

is over a mile across,
with 300-foot-high walls

and, at its center,
a 600-foot-deep crater.

Usually such an active volcano
near so many people

would be covered
in monitoring equipment,

but because it's remote
and dangerous,

Nyamuragira has none.

This is a rare opportunity

to gather data
for predicting future eruptions.

We're hoping to land
on top of the volcano,

right next to its active crater.

We need to collect some
really critical data up there

to understand what might happen
in the future.

This is one of
Africa's most active volcanoes,

and it has
a very complex history.

During the past 100 years,

it's erupted from its flanks
at least 30 times,

flooding the surrounding
farmland in molten rock,

though this hasn't happened

for the past five years.

In 2014,

for the first time
in almost a century,

a small lava lake developed
in the center of the crater.

So, the first thing
the scientists want to check

is whether that lava lake
is still there.

We're banking round now.

There's just sheer cliffs

right down to the lava lake,
which,

from what I can see
at the moment, seems to...

seems to be crystallized,

so seems to have turned
into rock.

But does this

have anything to do
with the volcano's behavior?

With the lava lake
apparently gone,

will the volcano return

to its cycle
of huge, destructive eruptions?

Belgian geologist Benoît Smets,

who works with local scientists,

specializes in geo-hazards.

I think we should first follow

the, the cracks...
Okay.

and then turn right right,
try to avoid them. Okay, cool.

He discusses
plans with Aldo Kane,

a former Royal Marine,

who's in charge
of the expedition's safety.

Across the caldera,
this is where the gas escapes,

so it's quite dangerous.

Okay, all right,

we'll get everyone out,

and then we'll get
a bit of a brief then.

Okay.

It's not just
the volcano that worries Aldo.

Just to be aware
there are armed groups

operating in and around
the, the slopes of the volcano.

If you do see someone
that's not from our group,

then get on the radio,
let me know.

There is a path and tracks
going through here,

so they are using it,
it is accessible to them,

so keep your eyes peeled.

Any armed
groups that saw them fly in

could be heading to the summit,
so they can't stay long.

So, we've got two hours,
so we need to be back here,

everyone at the chopper
ready to go in two hours.

- Cool?
- Okay, sounds good.

Thanks, Aldo.

The urgent question for the team

is whether the current break
in large-scale eruptions

is coming to an end.

Kayla believes that the plume of
gases released by the volcano

will yield vital clues.

I want to find a place

where I can actually get
inside the plume

and put the gas box,

and that can tell me more
about the different chemicals

that are coming out
of the plume.

Monitoring the changes
in that gas chemistry

is what tells us whether
the system is changing,

whether it's moving
towards an eruption,

whether there's new, new magma
being input at the very base.

The gases really tell
the whole story.

Most volcanoes
have a magma chamber,

a reservoir of molten rock
deep underground

that fuels eruptions.

As the magma rises up
towards the surface,

it releases a mixture of gases.

A sudden increase in one gas,
called sulfur dioxide,

often signifies
an imminent eruption.

Kayla wants to discover the
concentration of sulfur dioxide

in the gas plume,

but it won't be easy.

I'm really...
yeah, I feel, I feel like

we're really pushed for time
here.

There is a lot of gas
coming out of here.

The problem for me is that
once it gets to the top,

it's, it's become
pretty diffuse,

which is why I'm having
to chase the plume around.

The team
also needs to check on activity

in the lava lake.

Kasereka Mahinda,
a geophysicist,

knows the summit
better than anyone

and can identify the best place
to see into the crater.

The best place to...

The best place is there,

because one time I stayed there,

you can see around the crater.

Okay. Yeah.

Most eruptions are driven

by a build-up of pressure
inside a volcano.

It's possible that the lava lake
that appeared in 2014

acted like a safety valve,

an open vent releasing pressure.

When Kasereka was last here,
the lava lake was still active,

a small cone erupting
in its center.

I was here,

you have active lava
in the crater,

very big, active lava.

But now, from
the helicopter, it looks as though

the lava lake
is no longer active.

If so, then the volcano
may have lost its safety valve

and could now be building
towards a major eruption.

With only two hours to try
and find out what's happening,

the team decides to split up.

Kayla heads off on her own
to get a gas sample,

while Kasereka leads the others

to the vantage point
overlooking the crater.

Kasereka works
at the Goma Volcano Observatory,

which carries out research
on volcanoes across the region.

The observatory's job

is not only to monitor
the risk of eruptions

but also the long-term effects

of living in such
a volcanically active area.

We look at the whole landscape,

you know, it's about...

they... all volcanoes
in the landscape, that's one.

But mainly we focus
on the two active volcanoes.

Still... we still also
monitoring the rest.

We do also measure the quality
of water people are drinking

to advise
the health authorities.

Mathieu
Yalire studies volcanic gases.

Together with fellow
volcanologist Dario Tedesco,

he's investigating
the volcano's effect

on the water supply in Sake.

This is part of our job,

to analyze water,

all samples we can get
around the region.

Volcanoes tap the inner earth,

releasing certain elements
into the environment

in much higher levels
than normal.

Some can be harmful.

Mathieu and Dario are interested
in one particular element:

fluorine, that dissolves
in water to form fluoride.

Many of the townspeople
have brown, stained teeth.

Not a sign of neglect

but possibly a condition
known as fluorosis,

too much fluoride in their diet.

Around the world

sodium fluoride is often added
to drinking water.

At low concentrations,
it helps prevent cavities,

but at higher levels,
it can cause problems.

Mathieu and Dario measure
the levels of fluoride.

The limit of this machine

is ten part per million,

and it says, "Over the limit."

The water has levels of fluoride

around ten times
the recommended safe limits--

concentrations
that can damage teeth,

bones, joints,
and even organ function.

And there is no easy remedy.

At present, we really don't have
any solution,

because the best solution

would be to bring water
from very far from here,

in, uh...
Masisi.

Masisi, Masisi area.

It's a very...

It's 20, 30 kilometers.

This is not only this village.

It's more or less
100,000 people or more

that live in the area.

There's another effect

of the elements thrown out
by the volcano,

one that benefits the community.

Between eruptions,
the lava and ash break down,

releasing nutrients
into the soil

and creating incredibly rich
and productive farmland.

It's why the market
is full of food.

For local people,

this combination
of risks and benefits

can lead to a complex mindset

of both fear and appreciation
of the volcano.

Back on Nyamuragira,

the scientists are trying
to figure out

what the volcano will do next.

Kasereka Mahinda
from the Goma Observatory

is leading them to a viewpoint
over the crater

to help them assess

if the lava lake
that formed in 2014

is still active.

Oh, wow.

As you walk towards the edges
of these craters,

you get that feeling
in your stomach,

like you're about to go off
the edge of the world.

The crater is dark.

It looks as though

the activity Kasereka observed
in the lava lake

has now stopped.

To be sure,

Benoît and his colleagues
set up a thermal camera

to check
if there's any magma moving

beneath the thin crust
of black rock.

But that means getting

uncomfortably close to the edge.

Just go careful on that edge,

this entire edge,

even under where
your camera is there,

is over-hanging.

That's millions of tonnes
of rock there,

and they're right
on the edge of it.

They check the temperature.

Intense heat would mean
the vent is still active.

So what's the
temperature down on the base?

So everything has
the quite same temperature,

about 45 to 50 degrees Celsius.

Although quite hot,

50 degrees Celsius,
or 120 degrees Fahrenheit,

is not hot enough

for there to be magma
near the surface.

It's totally dead.

No activity left at all.

And the question is now,

is it just a break
or is it just finished?

It means that
the activity may change.

With no active
lava and a solidified crater floor,

pressure could be building
inside the volcano.

The volcanic
activity that we see

is only a very very small part
of the real volcanic activity.

There is much more happening
below the surface.

Some of the best clues

of what's happening
beneath the surface

are the gases given off
by the volcano.

They could reveal
if new lava is rising up inside,

threatening an eruption.

That makes
Kayla's gas measurements

all the more important.

But getting a sample
is proving difficult.

Unfortunately, the
best place where the gas is coming up

is also on, I think,
the most precarious part

of the entire crater rim.

It's why I'm not over there,
where its gassiest.

Is that... these thick
layers of ash,

that looks like
the most unstable,

but I'm just trying to get

as close as I can
without being unsafe.

Given the
dangers of gathering data,

Kasereka sets up
a simple instrument

he knows will be helpful
in understanding the volcano.

I need to set up my...

You're setting up here?
Yeah?

The observatory is trying

to establish a set
of baseline measurements

to spot changes in the volcano

that could signal an eruption.

So what are you gonna
set up here?

I set up the thermometer
to measure the temperature.

So, temperature measurements?
Yes.

Kasereka's focus

is the fumaroles
found across the crater,

cracks and openings
that can reach all the way down

to the magma chamber.

Measuring their temperature

can reveal what's happening
deep inside the volcano.

You know, we'll see if there,

the temperature increase or not.

Okay.

So I can tell if the magma
is coming up or not.

As magma
moves up inside the volcano

before an eruption,

the fumarole temperature
increases dramatically.

But to spot that,

a set of baseline measurements
is essential.

We've lowered the probe in

about a meter, meter and a half.

Yeah, this one will record
every five minutes;

Okay.
I try to reduce the minutes

because we don't have
enough time.

There's no screen
on the data logger,

so we can't see what the
temperatures are at the moment.

We have to wait

till we go back and plug it in.

Yeah, I have to go back
to my office,

Okay... okay.

'cause I have some software
to analyze, yeah.

This kind of data

could ultimately help
predict future eruptions.

With little time remaining,

Benoît is also determined
to squeeze in

one last experiment

that could reveal pressure
building within the volcano.

I would like you to follow

the drone with binoculars

to be sure I don't crash it.

Years of
observations around the world

have shown that
before an eruption,

increasing pressure can change
the shape of a volcano,

making it swell.

Perhaps the most extreme example

is Mount St. Helen's
in Washington state.

In 1980,
the north side of the volcano

bulged outwards some 270 feet

just a month
before its violent eruption.

Usually scientists are looking
for much more subtle changes,

which can take months
of monitoring

with a whole range
of ground-based sensors.

That's not possible here,

so Benoît has come up
with a high-tech solution.

I'm using a drone to take
pictures of the big crater

in different viewpoints.

And with this set of images,

I will be able to create
a 3D model of the big crater.

The computer
model Benoît creates

is a 3D snapshot of what
the crater looks like today.

Comparing it to images captured
on future visits

will allow him to spot
small changes in the terrain,

which may precede
an impending eruption.

Benoît has just enough time
to finish his survey.

The two hours are up,
and weather is closing in.

We are a long
way from the helicopter,

and there's a huge bank of cloud

that's coming our way,

so I think we take
the weather window

and we bug out.

If the storm hits,

the helicopter will not be able
to take off,

leaving the team stranded
on the summit.

If you need me to carry
anything, let me know.

Okay.
There's some space in my pack.

And we still
need to pick Kayla up

on the way as well,

'cause she's still
over there doing her gas box.

It's been a
frustrating day for Kayla,

who hasn't managed to capture
any useful data.

It's just
so hard to work in places like this,

where access
is nearly impossible,

and then when you get access,
you have two hours.

It's just not enough.

Even so,

this rare visit
has been worthwhile.

They've confirmed that the
lava lake that appeared in 2014

is no longer active,

raising the possibility

that the volcano may once again

be building
towards a major eruption.

If so,

the new monitoring equipment
they've left behind

may help forecast that event.

As the team departs,

they turn their attention

to another goal
of their expedition:

investigating what makes
this part of Africa...

so intensely volcanic.

It's amazing
from up here, the view you get.

From the ground,
it was spectacular,

but from here,

it is absolutely something else.

This is flat land

with these volcanoes
just punching through

absolutely everywhere.

The entire area is
filled with evidence of volcanic activity.

Each one of these small hills
is an extinct volcanic cone.

But what is the impact

of living
in such a volcanic landscape?

To find out,
the team travels to Goma,

a city of almost
a million people

that lies south of Nyamuragira

and another giant volcano,

Nyiragongo.

Nyiragongo last erupted in 2002,

sending rivers of lava
into the heart of Goma,

causing death and destruction.

The city has since recovered
and is growing.

Today Chris and Aldo are heading
to a local boxing gym.

Wow, check this out.

They're here
to learn about the relationship

between the area's
volcanic history,

its ongoing instability,

and what local people are doing

to address the trauma
of violence.

Continuing unrest here

means that children
often have little choice

but to fight in the armed gangs

and militias
that operate around Goma.

Some of the men in this gym
were once child soldiers.

The discipline of boxing

provides a way for them
to escape their violent past.

The continuing unrest
and use of child soldiers

are driven by the extraordinary
mineral wealth of the region,

especially one mineral

that plays a crucial role
in modern life.

This is the mineral coltan,

this dark-colored mineral here.

It's the kind of mineral

I'd expect to find
in an area like this.

And any touchscreen phone,
laptop,

anything with a transistor

will have tantalum,
which is the tan of the coltan.

The explosion in smartphones

and other electronics

means coltan is
in constant demand.

Even small mines
can generate huge profits,

but in this region,

militias control
many of the mines.

The income means
they can recruit young people,

fueling the ongoing violence.

It's very hard
to hold this in your hand,

knowing how much we desire it,

and knowing
what it leaves behind

and where it comes from.

Bonjour, Kibo.

The head of the gym, Kibomango,

is a former child soldier

who now tries
to help young people

rebuild their lives.

And you're happy for
us to join in some, some training?

Joining, joining,
no problem, no problem, yes.

Aldo's
fascinated by Kibomango's story,

because like him, Aldo became
a soldier at an early age.

So, Kibo, when
did you join the army?

Which is two years younger
than I was when I joined up.

How long did you serve
in the, uh, in the army?

Although Aldo
joined the Royal Marines at 16,

legally he couldn't see
frontline action

until he was 18,

unlike Kibomango
and the young people here.

I wouldn't mind betting
that what Kibomango's doing here

to run this boxing club

is partly for his own therapy.

As a child soldier,

he's going to have seen
some pretty nasty stuff.

After the workout,

Aldo has a chance to take on
the man himself.

Kibomango is
a former Congolese champion.

In a poor and job-starved area,

militias are one
of the few sources

of money and employment.

It's a vicious cycle.

The chaos in the region

helps gangs control
the mineral wealth,

and in turn the mineral wealth
allows the gangs

to maintain the chaos.

There are efforts underway
to break the cycle

by promoting a more sustainable
use of the resources

created by the volcanoes.

They focus on
the Virunga National Park,

a vast nature reserve covering
around 3,000 square miles.

Its fertile volcanic soils

make it one of the
most diverse parks on the planet

and one of the few places

where it's still possible
to see mountain gorillas.

These highly social animals

thrive in this lush
forest habitat,

eating mainly leaves, shoots,
and stems.

Thousands of people come to see
the gorillas,

generating cash that's used
to create local jobs.

But following attacks
by poachers and criminal gangs,

the park had to close
temporarily,

another setback for a region

where volcanic riches
have the potential

to create
a very different future.

But what makes this area
so volcanically active

in the first place?

It's a question the scientists
are determined to answer.

From the helicopter,

I got a, like, almost
a once-in-a-lifetime view

of the entire
volcanic landscape.

And what really struck me
was the amount of volcanism

and the amount
of volcanoes here.

We have hundreds
and hundreds of them.

This extraordinary
concentration of volcanic activity

is related to a vast chain
of mountains and valleys.

The East African Rift.

It's a massive
geological feature...

stretching nearly 4,000 miles

up the eastern side
of the continent,

and the Goma volcanoes are
at the midpoint of the rift.

The earth's outer crust

is divided into giant slabs
called tectonic plates.

Along the East African Rift,

the tectonic plate is splitting,

and the two sides of the rift
are moving away from each other

as the continent
slowly rips apart.

If the split continues
over millions of years,

a new ocean
and continent will form.

But many rifts
don't fully develop.

The waters of the Mississippi

now fill the scar left
by a failed rift

when a huge section
of what's now the Midwest

started to tear apart
around a billion years ago--

and then stopped.

Will the East African Rift
also fail?

The answer hinges
on a controversial theory.

So, one thing it could be

is something called
a mantle plume,

that's a column
of deep, hot material,

which is rising up
towards the earth's surface.

As it comes
to the earth's surface,

it can weaken the plate,

and it can actually
force the plates apart,

but some of that melts,

some of that magma
can also come out

onto the earth's surface
and build volcanoes.

The earth's
mantle lies between its dense core

and its thin crust.

The presence of a mantle plume,

a huge column of heat
and melted rock

rising from deep
beneath the region,

would explain why there
are so many volcanoes here.

If a plume exists,

then the enormous heat
and energy it brings

could keep the rift active

long enough
to split Africa apart.

Like all geological theories,

we really need to go out
into the landscape

and look
for additional evidence.

So along with
Kayla, Chris goes on the hunt

for evidence of
a distinctively deep upwelling

of heat and magma,

the signature of a mantle plume.

The first place
they want to look

is one of the extinct
volcanic cones,

common in the region.

I'm really interested
to see some of the smaller cones,

because we've been looking
at Nyiragongo, Nyamuragira,

you know, the big boys.

There's so much information that
the smaller cones can have too.

Their destination is Lac Vert,

the "Green Lake,"
just outside Goma.

Wow, look at that.

Today it's a 300-foot climb down

from the crater rim to the lake.

People bathe
and wash clothes here,

but around 500 years ago,

this was an active volcano.

Chris and Kayla want to know

what sort of eruption
formed Lac Vert,

and whether it could be linked

to the presence
of a mantle plume.

They also want to find out if
this volcano could erupt again,

and what that would mean
for the city of Goma.

They start
by examining the rocks

that make up the volcanic cone.

For many years
the sides have been quarried,

so with a little effort...

You got to go over the head.

Over the head?

Yeah.

...it's easy to get
their hands on some samples.

None of this is actually lava,

this is all ash,
these are all ash deposits.

And that means this was magma

that came up through the ground,

was exploded onto the surface

and absolutely ripped apart

into very, very fine pieces
that you can see here.

Imagine how much energy
it would take

to take solid rock,

and, and just explode it
into these tiny, tiny bits.

That screams to me that
there was an interaction

with the water
when this actually erupted.

Goma sits in the middle

of a string of craters
like Lac Vert,

each formed
by explosive eruptions,

and each capable of delivering
a devastating blast.

The eruptions are caused

by magma welling up
from underground.

When the magma hits a layer
saturated with water,

the extreme heat instantly
turns the water to steam,

triggering a powerful explosion.

This generates huge amounts
of fine-grained ash,

just like the deposits
found here--

clear evidence that Lac Vert

was formed by this type
of explosive eruption.

The sides of the crater
also reveal something else:

this wasn't a single event.

What strikes me,

as somebody who's interested
in sedimentology,

is how many layers of rock
there are like this.

The layering
in the rock behind us,

I wouldn't want to go over there
and count them,

but there's clearly hundreds
and hundreds

of giant explosions

associated with
this catastrophic eruption.

It may be about
five centuries since the last eruption,

but the danger of a new one
is very real.

We've still got lots
of volcanism here,

we're still right next
to the lake,

we can see in Lac Vert,
the water table is right here.

There's all
the ingredients there

for this to happen again.

A powerful new eruption

along this densely populated
shoreline,

or in the city of Goma itself,

would have a devastating impact.

But there might be
warning signs.

As magma moves up
towards the surface

through underground cracks,

it forces the earth apart,

creating swarms
of mini-earthquakes,

which instruments
called seismometers can detect.

Joshua Subira
of the Goma Observatory

explains that seismometers

have been placed
next to the volcanoes

and along Lake Kivu
near the city of Goma.

This network of
seismometers is an essential tool

in the effort
to forecast eruptions here,

where so many lives are at risk.

But neither seismometers
nor cones like Lac Vert

can tell Chris and Kayla

whether the heat and magma
that create these volcanoes

is coming from a mantle plume.

I think we need to get deeper

into this landscape

and try and uncover
what's really driving everything

from the biggest,
biggest scale sense.

One place
they have yet to explore

could hold the answer.

Lake Kivu.

Joining Dario Tedesco
and Mathieu Yalire

from the Goma Volcano
Observatory,

Chris and Kayla head out
on the waters of the vast lake

that lies directly south
of Goma.

Lurking in its depths
is a huge hidden danger,

worse than anything
they've seen so far.

It could also hold
the vital clue

about whether a mantle plume

is driving
the volcanic activity here.

Maybe now we're ready
to put this thing in the water, yeah?

The key is to get a water sample

from the deepest part
of the lake.

Let's try not
to lose everything.

Mathieu and
Dario drop an open sample bottle

down to a depth of 55 meters,
about 180 feet.

50 meters...

and here we have 55 meters.

If you want to see it...
I'll stand it.

There it goes.
Yep.

We'll leave it.

A heavy weight
is then sent down the rope

to trigger the mechanism
that closes the bottle.

You can feel the weight of that,

you can feel
as I'm dragging it up,

pushing the water out of the way
as I bring this thing up.

I think at five.

Yes, here is it.

And look...
wait, wait wait.

Look at the...
the gas coming out.

Come, come here.
Oh, my gosh.

Yes, you see?

Like a carbonated drink,

the bubbles consist
of gas suddenly released

from the water sample.

This is the danger lurking
in the lake.

When you open...

You can hear it.

It's like
opening a bottle of pop.

Yeah, exactly.

You see see the...
It looks like a soda,

it's all completely carbonated.

It's 99% is carbon dioxide.

99%?
Yeah.

The bottom of the lake

contains the potentially lethal
suffocating gas,

carbon dioxide.

It's given off

by the constant
volcanic activity

beneath the Goma region,

seeping into the lake
from the underlying bedrock.

Its presence is
a serious threat.

Lake Nyos in Cameroon

also has volcanic carbon dioxide
trapped in its depths.

On the night of August 21, 1986,

a giant lethal pulse of the gas

escaped from the depths
of Lake Nyos,

flowing over the shoreline

and into surrounding fields
and villages.

Almost 2,000 people suffocated
as they slept,

and Lake Kivu
is far bigger than Lake Nyos.

All the lake has
a huge amount of CO2,

about, uh...

256 cubic kilometers.

That's
enough gas to cover an area

more than 50 times
the size of New York City

in a suffocating layer
20 feet deep.

The risk is that a
volcanic eruption or earthquake

could destabilize Lake Kivu,

releasing
its carbon dioxide gas,

threatening the lives
of thousands of people.

But there are efforts underway
to prevent that,

and the group is going to see
an experimental project.

This is one of the most
amazing things I have ever seen.

We're in this glass flat bay,

and all of a sudden,
you come to this platform,

and it's just...
all hell has broken loose.

It's a massive
amount of pressure that...

it's almost like a geyser

- just spewing stuff.
- It is a geyser.

It is a geyser?
It is a geyser,

and we don't see
the geyser itself,

just because
there is something on top.

The core that is just 50 meters

in order not to let
the geyser blow.

Salty water,
another product of volcanic activity,

seeps into the deeper sections
of the lake,

forming a dense layer
that acts like a lid,

trapping the carbon dioxide
below.

The aim is to find a way of
slowly releasing the trapped gas

at concentrations
that don't endanger people.

A pipe runs down
from the platform

into
the carbon dioxide-rich layers.

The water saturated with gas
flows up the pipe

in a controlled release,

allowing the carbon dioxide
to mix with the air,

making it harmless.

This is a pilot

to see if there is a way to
de-gas this part of the lake.

If it succeeds,
we make a very big one

to put the... a very big amount
of CO2 in the air.

The controlled release

of the carbon dioxide reservoir
at the bottom of the lake

could prevent a future disaster;

but it's a massive project
and very expensive,

although efforts
to commercialize methane,

or natural gas, also found
at the bottom of the lake,

could help defray the cost.

Meanwhile, the dangerous
carbon dioxide in Lake Kivu

provides a valuable clue

to what's driving the area's
many volcanoes.

Where is the carbon
dioxide actually coming from?

Most of the carbon dioxide

that we collect
all over the lake

comes straight
from the mountain.

This is probably
the best findings we have.

The carbon
dioxide they collect here

bears a distinctive
chemical signature,

revealing its origins were deep
in the mantle,

the thick layer

between the earth's crust
and its core.

Here in the Goma region,

the earth's mantle is
at least 20 miles

beneath the surface.

Only a giant mantle plume,
a huge upwelling of magma,

could bring gas up
from such a depth.

The idea that there's
a mantle plume underneath here,

there's some evidence
at the bottom of the lake,

I just never thought

that would be something
we'd find out.

It's really the last,
the last piece of the puzzle

in this landscape, I think.

The existence of a mantle plume

bringing up extreme heat
from the depths

means the East African Rift
will likely continue.

Africa may eventually
tear apart.

Fortunately,
not for many millions of years.

But the scientists believe

the energy unleashed
by the plume

explains the extraordinary
volcanic activity

witnessed
during their expedition.

The CO2 that's
sitting in the bottom of this lake,

all of the gases,

the sulfur that you can smell,

it's all coming straight
out of the mantle.

It's just streaming off,
this upwelling plume of material

that's delivering heat,
energy, chemistry

to the whole landscape.

To the volcanoes we've been on,

the bottom of this lake,

it's all connected
to the same huge process.

After three weeks

the expedition has come
to an end.

It's been grueling,

but the team has gained
unprecedented insights

into the volcanoes

that dominate this region.

On Nyamuragira,

their aerial survey is
an important step

toward predicting
future eruptions.

And in the depths of Lake Kivu,

they found evidence
that a vast mantle plume

drives the region's
intense volcanism,

which may ultimately
split Africa in two.

The people here
live side by side

with geological forces

that are reshaping
the face of our planet.

If you live in this
amazing, amazing place,

you can live with the hazards,

but the hazards cannot be

at the front of your mind
all the time.

It would just stop you
from doing anything, I'd guess.

The knowledge
gained on the expedition,

working with local scientists,

is vital to better prepare
the people of Goma

for future eruptions...

which are bound to occur.

We have
two active volcanoes now.

The city became very big,

many people in Goma.

The gas in Lake Kivu,
it will make problem.

Maybe we have to monitor
and continue to monitor,

to make warning in time.

These forces can be
understood but never completely controlled.

This will always be

one of the world's most
extraordinary places to live...

a landscape
of both deadly hazards

and incredible wonders.

We have this absolutely vast
volcanic landscape here,

and the people living
right on top of it.

It's my hope
that people can learn

to understand that landscape
better,

in order
to not only protect themselves

but also to reap the benefits
from it.

Hey!