NOVA

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, but no one knows the answer,

because these are among the least studied volcanoes

in the world.

Now an international team of scientists

is investigating these giants.

Their goal?

To predict future eruptions and save lives.

Everything we do to understand this volcano

is very important to avoid another disaster.

They're heading to the volcano known as Nyiragongo,

which towers over a rapidly growing city

of a million people.

An eruption in 2002 caused death and destruction.

I could see the lava flowing and wrecking all houses.

You could hear the noise.

To penetrate the volcano's secrets,

the scientific team descends into the crater itself.

It's treacherous.

Rock!

Everything's moving.

Nothing is stable.

But with lives in the balance...

Rock!

...the stakes could not be higher.

Oh, man, look at these rocks.

Just precariously balanced.

"Volcano on Fire," right now on "NOVA."

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Deep in central Africa

is one of the most spectacular, active,

and dangerous volcanoes on Earth.

That's terrifying.

There's literally nothing like this in the world.

This volcano, named Nyiragongo,

threatens almost a million people in this region.

Twice in recent memory

it has devastated the city of Goma.

The red river keeps flowing,

pouring out of the volcano and down towards Goma.

Violent conflict in this region

has often made it too dangerous

to mount any large scientific expeditions.

But a temporary peace opens the door

for a groundbreaking investigation.

Because this giant

is one of the least understood volcanoes in the world,

both threatening and life-giving.

A team of scientists will spend a week on Nyiragongo,

the volcano that towers over Goma.

Their goal is to find ways to predict

when this volcano will next erupt.

A huge spike in the amount of sulfur dioxide,

that could be something that happens before an eruption.

Their search for answers

will take them deep inside the crater...

I've just come over the edge.

...and into great danger.

If any of this rock goes here, that's it for both of us.

Now the team is on its way to the 11,400-foot-high Nyiragongo.

It lies on the Democratic Republic of Congo's

eastern border with Rwanda.

Its steep cone,

created by successive eruptions over centuries,

rises over a mile above Goma and the surrounding landscape.

Forecasting eruptions is difficult and uncertain

even for well-studied volcanoes,

but it can save lives

by giving people time to get out of harm's way.

23, 24, 25...

To achieve that,

the scientists have brought an array of equipment

to investigate this volcano in many different ways.

Just take care that the men take the heavy bags...

Yes.

Leading the science team

is Belgian volcanologist Benoît Smets.

Studying Nyiragongo is very important for me,

because this volcano is very dangerous.

It, uh, threaten a lot of people.

Everything we do to understand this volcano

is very important to avoid another disaster like in 2002.

Joining him are scientists from the local volcano observatory,

who want to install instruments on the crater rim.

Joshua Subira has studied this volcano for several years

and knows firsthand how difficult the climb will be.

Pourquoi?

Actually that's the one I'm worried about,

because I don't want someone to drop it.

American geologists Jeff Johnson and Kayla lacovino

are worried about damage to the instruments they brought

to help identify warnings of an eruption.

No, the sun's out down here.

Did you have a good night last night?

Ab solutely hammered it down.

Former Royal Marine Aldo Kane is in charge

of getting everyone and everything

to the top of the volcano.

We've got science kit, expedition kit, rigging kit,

food, water,

nearly four tons of kit that's going up the hill today.

Nyiragongo's crater rim is 6,500 feet above the jungle

and only accessible on foot.

It takes six hours

for the team to reach its steep upper slopes.

The weather's closed in.

It's cold.

But their reward

is a view of one of Earth's great natural wonders.

Oh, my God, that is so incredible.

There's literally nothing like this in the world.

There are six permanent lava lakes on Earth.

You are standing looking into one of those six.

Of those six lava lakes,

they are all babies compared to this size of...

Yeah, they are.

All other global lava lakes

could fit into this lava lake,

with tons of room left over.

This lava lake is enormous.

The sheer size of it, I think, is just hard to fathom.

The crater is almost a mile in diameter.

Inside is a permanent cauldron of molten rock.

And it constantly churns

at almost 2,000 degrees Fahrenheit.

It's ferocious... It feels very alive.

I mean, even when we're silent,

there's that constant roar.

It's just, doesn't let up at all.

British geologist Chris Jackson

has studied volcanic landscapes across the world.

For him, volcano prediction

is a scientific and humanitarian challenge.

Yesterday, he traveled in through the city

that lies at the foot of the volcano.

It's amazing to think

that there's such a threat posed by that volcano,

yet because of that volcano, you can build houses

and some sort of infrastructure.

Goma, a city of almost a million people,

is growing and modernizing rapidly.

Houses are going up everywhere,

with foundations made from volcanic lava.

This is incredibly exciting

to be joining an expedition like this,

to do cutting-edge, critical science

for the people living in the shadow

of this giant volcano.

In the outskirts of the city,

the volcano is virtually a next-door neighbor.

This place may look like a building site,

but it's a building site sitting directly on top

of this, this lava, which was erupted only 15 years ago

from the volcano of Nyiragongo.

For the people who live in the city of Goma,

this is just a disaster waiting to happen.

A disaster that has happened many times before.

Daylight, and some of the first pictures

reveal a black blanket of lava covering entire neighborhoods.

When Nyiragongo erupted in 2002,

lava flows split the city in three,

destroying many homes

and causing about a hundred deaths

as people fled for their lives.

The red river keeps flowing,

pouring out of the volcano and down towards Goma.

I could see people walking on this main road

fleeing the volcano.

Caleb Kabanda, a local journalist,

witnessed the whole eruption

from the center of Goma.

You know, it was a lake of lava destroying everything.

I could see lot of smoke,

and the lava flowing and wrecking all houses.

You could hear the noise.

I was very scared.

The lava has been flowing for two days now.

It shows no sign of stopping.

Some places you could see the fire burning.

Many people panicked,

because it was a disaster to the whole city.

You see all the houses you knew were destroyed.

It was really, uh, terrible

and I thought that this is the end of Goma.

As if the people of Goma had not suffered enough,

this was a day that brought them more death,

more tragedy.

Fireballs filled the sky

after a petrol station here exploded.

Fuel cans leapt into the air.

Eruptions like this are no surprise,

because Nyiragongo is part of one

of the largest volcanically active zones on Earth,

the East African Rift,

a vast scar created by the pulling apart of the land.