Nova (1974–…): Season 46, Episode 6 - The Next Pompeii - full transcript

In Southern Italy,
a city under threat:

Naples, flanked by two
dangerous volcanoes.

On one side, Vesuvius,

destroyer of ancient Pompeii.

None of them met
with a peaceful death.

They were afraid,
they were panicked,

and it was terrifying.

And on the other, Campi Flegrei,

an invisible monster

that threatens
three million people.

This is the most dangerous
volcano in the world.



Now scientists are seeing
increases in volcanic activity

and are scrambling to unlock
the inner secrets

of these volcanoes,
before it's too late.

There's no choice.

You just have to go to a place

which is relatively difficult
to get to.

Can they find ways to predict
the next eruption?

This is evidence of how fast
things change in this area.

Can they save
this jewel of Italy

from another disaster?

This volcano can erupt
at any time...

Even tomorrow.

Could Naples become
the next Pompeii?

Right now, on "NOVA."



Major funding for "NOVA"
is provided by the following:

More than 1,000 volcanoes
around the world are active.

Driven by Earth's
fiery interior,

they can erupt at any time,

blasting molten rock and ash
into the sky

with frightening power
and speed.

And unleashing
deadly destruction

on those who live
in their shadow.

Volcanoes have the power
to kill thousands

in the blink of an eye.

A stark warning
for the people who live here,

in the beautiful port city
of Naples in Southern Italy.

This ancient
and vibrant metropolis

of over three million people

might seem an ideal place
to call home.

But looks can be deceiving.

It is built right next
to not one,

but two active volcanoes.

Each has a history
of catastrophic eruptions.

To the east is
the well-known Vesuvius,

a classic, cone-shaped volcano

that has claimed
thousands of lives,

erupting as recently as 1944.

And to the west is
an almost unknown volcano,

Campi Flegrei,
hidden below ground

in an area where
hundreds of thousands live.

It doesn't even look
like a volcano.

And yet, it has the potential
to be far more destructive

than its more famous neighbor.

Today, there are ominous signs

that both volcanoes
are still active:

swirling clouds of gas
and bubbling pools of mud.

What do these mean
about the likelihood

of a major eruption?

It's hard to imagine the impact

on such
a densely populated city.

And yet, it's happened before.

Just 15 miles
from central Naples

is the site of one
of history's most infamous

volcanic disasters.

The Roman city of Pompeii.

In year 79 of the Common Era...

Vesuvius exploded
and buried the entire city

in over a dozen feet of ash.

Over the last 150 years,

archaeologists
have been carefully

uncovering the remains...

Revealing a scene
of carnage and death.

A city and its people,
frozen in time

at the exact moment
an eruption struck.

Among these ruins
are crucial lessons

about how a volcanic disaster
can unfold

and evidence of just how
suddenly an eruption can strike.

For archaeologist Kevin Dicus,

this human tragedy is
a stark warning from history.

Walking around the ruins today,
it's really easy to forget

that this was actually
a functioning Roman town

2,000 years ago.

Within the city walls,
perhaps 15,000 people

of different classes,
different ethnic makeup,

all trying to survive
in this city.

Remarkably, everyday items,
like food,

survived the eruption.

Walnuts.

Walnut kernels, already peeled.

One of these food items shows
how the people of Pompeii

were caught completely off-guard
when Vesuvius erupted.

This one is one of the 81 breads

found inside an oven
that was fully operational

- at the moment of the eruption.
- Wow.

With one peculiarity.

There is still the fingerprint
from the baker,

the baker's thumb.

Oh, my gosh.

This really brings
a human element to this, right?

Bread being baked
at the time of the eruption,

and the baker...
hopefully the baker escaped,

hopefully he lived
the rest of his days

baking bread somewhere else,
but we have no idea.

But it really it tells us
something about the eruption,

how unexpected it was.

In the face
of this sudden cataclysm,

many of Pompeii's residents fled
in blind panic.

But some chose to stay behind
and shelter in the city.

They paid the ultimate price.

Their last desperate moments
preserved for eternity,

as Pompeii's
most evocative remains.

These are but a few

of the approximately
2,000 victims

that decided to wait out
the eruption

and, of course, didn't make it.

Now, what we have here are not
the bodies themselves,

but these are the exact poses
of the victims

at the very last moments
of their lives.

After their death,
they were covered with ash.

Over time, the soft tissue
decayed, liquefied,

and leaked through the ash,
leaving behind these voids.

Archaeologists pour in
plaster of Paris,

leave them to dry,
and we get these exact poses.

This is a really macabre
reminder

of what can happen
in the blink of an eye

to an entire city.

Could Vesuvius erupt today
with such violence?

Do millions of people risk
the same fate

as their ancestors?

Centuries have passed,
but one thing hasn't changed.

Vesuvius is still active.

Driven by a geological collision

that has been shaping this part
of Italy for millions of years.

To the east of Naples,

two of the planet's
vast tectonic plates

are crashing into each other.

The African plate is being
forced downwards

in a process called subduction.

As it descends toward
the hot center of the Earth,

it gets warmer.

This causes rocks to melt
and turn into liquid magma,

which rises towards the surface.

To the east of Naples,

there are weaknesses
in the rock.

Here
the magma can break through.

And if it has enough power,

it can even trigger an eruption.

It's this constant subduction
which keeps Vesuvius active

and fuels its eruptions.

Due to this ever-present danger,

the volcano is kept
under 24-hour surveillance.

At the Osservatorio Vesuviano,

scientists are watching
for the warning signs

of an imminent eruption.

We have one millions
and five hundred people

that are at high risk
in case of eruption.

From a high-tech control center,

Francesca and her colleagues
pick up seismic activity...

Movements in the Earth's crust.

In these screens,
we see all the signals

that came from the sensors

that we have installed
on Vesuvius.

In all, there are 150 sensors
on the volcano,

all listening for earthquakes.

These can indicate
if an eruption is on the way.

Each eruption begins when
magma starts to rise upwards

from deep in the Earth.

It pushes through weaknesses
in the rocks

towards the surface.

If its way is blocked,

it builds up
more and more pressure

until it fractures
the rocks apart.

This is so violent,

it generates earthquakes
which the scientists can detect

at the surface.

Every time the magma
breaks through the rock,

it generates a new quake

until the magma erupts
out of the volcano.

Francesca and her colleagues
detect minor earthquakes

nearly every week.

And this constant monitoring
is vital.

Vesuvius can change
very quickly.

We have active volcano,
and of course,

if a volcano is active,
for sure,

it will erupt again.

We don't know when.

Mindful of Vesuvius's
lethal past,

the observatory's scientists
don't rely solely

on earthquake monitoring.

They have another,
more hands-on way

to monitor the magma.

At the summit of Mount Vesuvius
is a vast crater,

nearly 1,000 feet deep.

Every month,

a monitoring team carefully
descends into this gaping hole

to gather data.

Today, geologist Chris Jackson
is joining them.

Some of the critical bits
of data

about the volcano's behavior and
the kind of threat it can pose,

they can only be gotten
from one particular location.

So there's no choice

about trying to collect it
somewhere easy,

you just have to go to a place

which is relatively difficult
to get to.

Their mission is to collect
vital gas samples.

These could hold clues

about how close the magma is
to the surface.

To get them,
they need to climb down

into the heart
of Vesuvius's massive crater.

Their target is a fumarole,
a gap in the rock

where gases
from the magma escape.

The team takes samples

to measure
the levels of one these gases...

Carbon dioxide.

What we are really interested in
here

are spikes in carbon dioxide
coming out of the volcano,

because that spike
in carbon dioxide

might mean that there's new
magma coming into the volcano,

which could occur
immediately before it erupts.

Rising magma experiences
less and less pressure,

causing it to release
more and more carbon dioxide.

The magma within a volcano

is a little like the soda
within this soda bottle.

Both of them contain
carbon dioxide,

so CO2 dissolved within them.

As the pressure drops...

the gas comes out of solution,

forming bubbles,
which can escape to the surface.

The reasons the bubbles
came out of the soda

is because we released
the pressure.

And the same happens when magma
rises up within a volcano.

It is that decreasing pressure
that allows the gas bubbles

to expand and to eventually come
out the top of the volcano.

Constant monitoring of
carbon dioxide and earthquakes

is vital to predicting
when Vesuvius might erupt again.

But this isn't enough to keep
the people of Naples safe.

For that, scientists also need
to understand

the consequences of an eruption.

Who would be most at risk?

And what dangers
would they face?

Clues can be uncovered
by analyzing past eruptions.

Even if they happened
2,000 years ago,

such as the annihilation
of Pompeii.

Remarkably,
there was a witness...

The Roman author
Pliny the Younger.

This is the very first
eyewitness account

of a major volcanic eruption.

"On August 24,
in the early afternoon,

"my mother drew
my uncle's attention

"to a cloud of unusual size
and appearance.

"Its general appearance
can be best expressed

as being like a pine tree."

We don't think of a pine tree

as an analogy for the cloud
of a volcanic eruption.

But, if you come to Italy,
if you come to Campania

and see the type of pine tree
that grows here,

you realize
that what Pliny was describing

is a perfect analogy.

In modern times,
scientists have seen

this same distinctive,
pine-tree-shaped cloud

again and again.

Called Plinian eruptions,

these are the most explosive
and the most lethal.

But how exactly

did a Plinian eruption kill
around 2,000 people in Pompeii?

Volcanologist Claudio Scarpati
looks to the ash left behind

for clues.

In this deposit,
we see different layers:

coarse layers, fine layers.

These different layers
are different phases

of the eruption.

The bottom layer was deposited

in the first phase
of the eruption.

It consists of pumice,

small pieces
of white volcanic rock.

Amazingly, their size
can be used to calculate

how high the eruption reached,

an indication of its power.

The size of the particles
is proportional

to the height of the column.

Taking these fragments
all around the volcano,

volcanologists were able
to define the height

of the 79 A.D. eruption column

as 32 kilometers high.

The Roman people saw a column

that was 32 times
the height of Vesuvius.

This was a massive eruption.

Gas and pumice exploded out

at a rate of over one-and-a-half
million tons every second,

forming the distinctive
pine-tree-shaped cloud

of a Plinian eruption.

This reached 21 miles high

and was so vast,
it blocked out the sun.

Then it rained pumice down
on Pompeii and its inhabitants

for 18 hours solid.

Surprisingly,
this sustained bombardment

actually gave people
an opportunity to escape.

Pumice is such a light rock,

it didn't present
much of a threat

to those who decided to flee.

This fragment could hit you,
but without any problem.

We know from Pliny,

that if you just put a pillow
on your head,

you can survive this
first phase of the eruption.

But strangely,

hundreds of bodies
have been excavated

from this layer
of pumice fallout,

meaning they died during this
first phase of the eruption.

What killed them?

One clue is
the location of the bodies.

Most were found
inside buildings.

They had probably decided
to shelter in their homes

rather than flee.

Many seem to have died

from traumatic fractures
to their skulls.

Claudio thinks
these deadly blows to the head

are explained by the long
duration of sustained fallout...

18 agonizing hours.

These roofs were quite flat,

and so pumice accumulated,

and the overload was too high,

and so the roof just collapses.

If you stay inside the house

and the roof collapse
on your head,

you are probably killed.

Killed and then buried.

A warning for today.

2,000 years later,

Neapolitans still live
in flat-roofed houses.

We see that the roof
of the buildings of the towns

around Vesuvius are still flat.

So you could have
the same effect,

an overloading
of the modern roof,

and so in two, three hours,
this roof could collapse.

The tragedy of Pompeii warns
of the dangers

of pumice fallout.

But out of the 2,000 dead,
only about a third died

during this phase
of the eruption.

So what killed
the rest of the victims?

Once again,

the answers are in the layers
of volcanic ash

Vesuvius left behind.

There is a sudden change
from a coarse layer of pumice

to a band of fine material
just over one-inch thick.

This smooth layer is
characteristic

of the dramatic next phase
of a Plinian eruption...

A ground-hugging volcanic surge
called a pyroclastic flow.

This is the deadliest outpouring
a volcano can unleash.

It is an avalanche
of gas and rock

moving at up to 300 miles
per hour.

So why did Vesuvius

suddenly start to produce
a pyroclastic flow?

In a Plinian eruption,

the mass of material
in the column

grows and grows.

But there comes a point

where there is so much rock
and debris

that the eruption can
no longer support

all this weight.

The column collapses back
towards Earth,

creating an avalanche
of debris...

The pyroclastic flow.

The column collapsed,

and the gases and the solids
and everything moved down

like an avalanche.

In Pompeii,

the pyroclastic flow crashed
through the buildings

and inundated
people sheltering inside

in a dense blanket
of gas and fine ash.

This is what claimed
most victims in Pompeii.

Can you imagine the
air being replaced

by an impossibly large cloud
of ash and gas,

and trying so hard to fight
from breathing this in?

Here we have, for example,
this individual,

and how clearly you can see
his right hand

pressed against his mouth.

He no doubt had a cloth
of some sort,

trying to keep the ash
from going into his lungs,

and of course, it did not work.

That ash meets
your moist lung walls

and clings to it like plaster
on this wall here,

and that's the last breath.

But the shape
of some of the casts

suggests the pyroclastic flow

killed in
an even more gruesome way.

This cast in particular
is fascinating to me,

and what is so interesting
about it is the pose.

You can see this individual died
on his or her back,

but the arms are up,
the legs are up.

Why is this?

This is known
as the cadaveric spasm,

and it usually occurs
in atmospheres of intense heat.

Pyroclastic flows
can reach temperatures

of hundreds
of degrees Fahrenheit.

This is what caused
the victims to contort

into these strange shapes.

So when this pyroclastic flow
surged over the city,

it caused the muscles
to contract

and turn inwards.

You can see it
in many, many of these casts.

A lot of these individuals
display this cadaveric spasm.

These people died instantly.

The intense heat froze them

at the exact moment
the pyroclastic flow hit.

What happened to Pompeii
and its people

is a stark reminder of the
destructive power of volcanoes.

And it could happen again.

This is the reason

that scientists have to keep
monitoring Vesuvius's activity.

But there is
a far greater threat to Naples.

Vesuvius isn't the biggest
or most powerful volcano

in town.

On the other side of the city,

scientists have seen
an alarming increase

in volcanic activity.

Pisciarelli... a vast fumarole,
a vent of bubbling gas and mud.

In recent years,
it has grown larger

and turned into a destroyer.

A few hundred feet away,

expert in volcanic risk
Antonio Costa

is visiting a deserted building.

Inside, the walls and floors
are covered

in a thick layer
of solidified ooze,

and the air is filled
with the acrid smell of sulfur.

This building,
up to ten, 15 years ago,

was, like, a sort of a club

with a swimming pool there,
there was a bar.

People were pushed to abandon
this place,

because it's not anymore
inhabitable.

The volcanic vent has
claimed the entire building.

This hostile takeover began

when gas from the vent
punched holes

through the floor and walls.

Here you can even feel,
if you put the hand here...

It's terribly hot.

As the gas cools,
it releases dissolved minerals.

These stick together to form
the thick volcanic scum

which is now consuming
the entire house.

This is clearly evidence

of how fast change things
in this area.

So where is the volcano

that is driving
all this activity?

The vent is in an area
called Campi Flegrei,

which is home to hundreds
of thousands of people.

At first glance,
it's hard to spot the volcano.

Unless you have a trained eye.

So when we think of volcanoes,
we think of that.

Vesuvius,
the perfect conical shape,

with that beautiful crater
on top.

But at Campi Flegrei here,

there's also some evidence
that this is a volcano,

but it's, it's just
far more subtle.

Good?

Yeah.
Okay.

To take a better look
at the lay of the land,

Chris needs to take to the air.

A monitor connected to a drone
provides him

with a bird's-eye view
of Campi Flegrei.

So the first thing
you notice from up in the air

is, as we come round
to the shoreline,

towards the Bay of Naples,

we start to pick up
a prominent ridgeline

that comes all the way around
towards the main city center.

It's clearly curved.

And then within there,

it's a very densely populated
flat area here.

This ridgeline could
be telling us something

about a feature that is actually
forming this landscape,

an ancient, very large volcano.

And in particular, we are
actually looking at a caldera.

A caldera is
a collapsed volcano.

In the past,
Campi Flegrei was a flat plain.

Deep beneath
was a huge reservoir

of bubbling magma.

Then the magma started
moving upwards,

smashing through weaknesses
in the rock

and erupting powerfully.

But this left an empty void
beneath the surface.

With nothing left to support
the weight of the plain,

it collapsed downwards...

forming a crater
known as a caldera.

Radioactive dating of rocks
reveals

that Campi Flegrei's caldera
formed 15,000 years ago.

And at nearly eight miles wide,
it must have been created

by an incredibly large
and powerful eruption.

Volcanologist
Giuseppe Mastrolorenzo

thinks this sounds a warning
for modern-day Naples.

It is important to study
the past eruption

in order to imagine scenarios
for the next eruption,

because in geology,
what happened in the past

will happen also in the future.

The remains of the eruption

that formed
Campi Flegrei's caldera

can be found beneath the streets
of downtown Naples.

Here, there is a labyrinth
of narrow passageways.

These were hand-cut
thousands of years ago

to provide building materials
for Naples.

Today they are a treasure trove
of information

about the eruption.

This is the Neapolitan
Yellow Tuff formation.

Here, underground Naples,

we have several tens of meters
of this formation.

This rock has
a powdery consistency,

which points
to the most deadly event

in an eruption.

Here you can see the fine matrix
of fine particles of ash.

This is typical
of pyroclastic flows.

In Pompeii,
the pyroclastic flow,

which killed
more than 1,000 people

left behind a layer of ash
just over one inch thick.

But here, beneath
the very center of Naples,

the thickness
of the pyroclastic flow

reaches over 300 feet.

This eruption is
about ten times bigger

than the Pompeii
79 A.D. eruption.

If another eruption like this
will occur in the future,

all the people and buildings
of Naples will be buried

under hundreds of meters
of, of ash.

So nothing can resist
this eruption.

In Campi Flegrei, there are
hundreds of thousands of people

living directly on top
of an active volcano.

If it erupts,

deadly ash fallout
and pyroclastic flows

could even hit downtown Naples.

With so many lives at stake,
the pressure is on

to determine when this volcano
may erupt next.

So scientists are keeping an eye
on Pozzuoli,

the biggest town
inside Campi Flegrei's caldera.

This is the site
of an ancient Roman marketplace.

Remarkably,
these ruins could point to a way

of predicting the next eruption.

Within the remains is evidence
of dramatic ground movements.

The clues we're looking for
we can see here,

on the three marble columns.

And you'll notice

that after about ten to 20 feet
above their bases,

all three columns are full
of small holes.

These were holes produced
by clams.

They liked to burrow
into the marble

to form colonies.

The clams that made these holes
can't survive on dry land.

They live solely under the sea.

So at some point, these columns
must have been underwater.

Now, we know from studies
across the Mediterranean

that the sea level
has only changed

at most by a few feet
since Roman times.

If the sea level hasn't changed,

there is only
one other possibility.

It must be the land
that has risen and fallen.

This whole area must have sunk
into the sea

and then come back up again
at least once since Roman times.

In fact, the ground in
the caldera has a history

of rising and falling.

And eruptions are known

to follow periods
of intense uplift.

Eyewitness accounts describe
that in 1538,

the ground rose rapidly.

Two days later, a minor eruption
created this crater,

called Monte Nuovo,
on the outskirts of Pozzuoli.

In 1982,
the ground around the town

began to rise again
very quickly.

This prompted fears
of an imminent eruption.

Tiziana Vanorio lived
on the outskirts of Pozzuoli

during this period,

and remembers the chaos
it caused.

The first thing that became
unusable was the harbor,

because of the uplift.

The ocean floor
became so shallow,

so that the ferry
could not dock.

Over the next two years,

the ground lifted up
nearly six feet.

Then the earthquakes started.

On April 1, 1984,

more than 500 shocks overnight
struck the town of Pozzuoli.

Fearing the worst,
the authorities stepped in.

As the seismic activity
kept increasing in the area,

the town of Pozzuoli
was evacuated.

People had to flee
their own town,

because of the fear
of an impending eruption.

Pozzuoli overnight became
a ghost town.

But strangely,
the eruption never came.

Two years later,

people were allowed to return
to their homes,

but a big question remained:

Why hadn't Campi Flegrei
erupted?

Today,
Tiziana is a rock physicist,

and she is trying to answer
this very question.

This is a good one.
Hi, guys!

VANORIO: One thing piqued
always my curiosity:

why a place can withstand such
large and sustained deformation.

So we had to understand

why the rocks of the caldera
behaved this way.

One mile below the surface
of Campi Flegrei's caldera

is a layer of hard stone
known as caprock.

Could this rock contain
an explanation

for why the ground rose and fell
so much

without an eruption happening?

We want to understand
how this rock

would behave in the caldera

under the conditions
of temperature and pressure

they experience in the caldera.

A specialized chamber mimics
these conditions

and also subjects the samples
to extreme stress.

What she finds is that the rock
doesn't snap or fail instantly.

It actually bends.

What we can see
is that the caprock

is capable of withstanding
high level of stresses,

but also, it shows
from this bell shape

a ductile behavior,

which means
this rock is not brittle.

This finding may explain
what happened in Pozzuoli

in the 1980s.

Magma started moving
towards the surface,

where it heated fluids trapped
in the ground above.

These expanded,
pushing up the caprock.

As it was ductile,
it was flexible,

and bent upwards.

This put stress on the caprock,

which began to fracture,
generating the earthquakes.

But it didn't crack completely.

It could still resist the uplift
and prevent an eruption.

Tiziana wondered why the caprock
had such unusual strength.

Looking under
a high-powered microscope,

she was surprised
to find something

you don't normally see in stone.

The rock had formed a network
of fibers

that were knitted together.

The presence of fibers was
really an intriguing discovery,

because the fibers are
intertwined or braided together,

like the strands in a rope.

Tiziana thinks
these rope-like fibers

are the secret
of the caprock's strength

because she also sees them
in a man-made material

famous for its durability
and toughness.

The same fibers
that you can see here

come from Roman concrete.

The strength of Roman concrete
is one reason

so many of their structures
survive to this day.

Tougher and more durable
than modern-day concrete,

it was the Romans'
go-to construction material.

And the secret ingredient
in Roman concrete?

Volcanic ash,
called "pozzolana,"

mined in Campi Flegrei.

The Romans combined this
with other ingredients

to form their concrete.

Remarkably, it seems
a similar chemical process

takes place a mile below
in the volcano, under Pozzuoli.

The caprock is a natural version
of Roman concrete.

Its strength may have prevented
Campi Flegrei from erupting

in the 1980s.

But this strength
is also a liability.

To fracture the caprock
completely

would require colossal force.

And that would result

in an incredibly powerful
eruption.

Having a caprock that has
high strength and ductility

can be a blessing and a curse
in a caldera.

Today, Campi Flegrei's caprock
is once more under stress.

Since 2005, the ground has been
rising out of the sea.

And scientists think
that the protective caprock

is being weakened.

At Pisciarelli,
there is a shift in the gases

bubbling up
from Campi Flegrei's magma.

The first gas that is released
is carbon dioxide.

When most of the carbon dioxide
is escaped,

the magma start to release

increasing amount of water,
of steam.

Steam is the Achilles' heel
of the all-important caprock.

Because when steam condenses
to water,

it releases large amounts
of heat,

which starts to fracture
the rocks.

The rocks that cover the magma
become weaker,

so could favor an eruption.

A catastrophe in the making
for Naples

and the three million residents
threatened

by an eruption of Campi Flegrei.

Faced with this prospect,

the observatory has enhanced
its early-warning system,

installing additional sensors
across the caldera.

We have sensor to measure
ground deformations,

to measure anomalies in gravity,

to measure
the geochemical activity,

the temperature of the
fumaroles, and so on.

If there are big anomalies,

you have more probability
that an eruption is approaching.

And the scientists
are about to add

an ingenious new detector

to their early-warning system.

This will offer Naples
a unique form of protection.

It's the brainchild
of Luca de Siena.

To see how the volcano is
changing, deep underground,

he uses sound waves.

You could use dynamite
or any sort of explosion

to produce the wave,

but that's obviously impossible

in a metropolitan area
of 1.5 million people.

Instead, Luca found a surprising
and less disruptive source

of sound waves...

One that's already in place
and operating 24/7.

It was quite astonishing
when we discovered

that we could use just the noise

that the sea is producing
at all time

to see inside a volcano.

As the sea crashes
into the shore,

it produces a sound wave.

That in turn propagates
through the ground.

By measuring the velocity
of the wave,

Luca can tell the kind
of material it is encountering.

If it is traveling quickly,
it's passing through solid rock.

But if it slows down,

it's likely to be passing
through fluids, like magma.

Measuring the velocity

of different waves
crossing the caldera,

Luca has built up a 3D picture

of what lurks
beneath Campi Flegrei.

We gathered three years of data,

and what we got is this map,

where we have found
a sort of circular area,

which is low velocity.

Low velocity means that likely

there are hot fluids
inside this area.

This could be magma.

For the first time,

scientists can see
where the hot fluids are

across the entire caldera.

We know that
most of the fluid come

just under our feet, actually,

here, under the port,
in Pozzuoli.

But to know
if an eruption is on the way,

Luca needs to be able to see

if magma and hot fluids are
rising towards the surface.

For that level of detail,

he will have to expand
the network.

When it's up and running,

Naples will be the first city
in the world

able to track these movements
in real time.

If we measure this parameter
all across the caldera,

and we see that this parameter
is changing over here,

that's a marker

that a possible eruption
may happen.

This cutting-edge
early-warning system

could be the best way
of protecting Naples.

It could buy people vital time
to escape.

An unexpected Plinian eruption
of Campi Flegrei

would put millions of lives
at risk.

In this nightmare scenario,

the eruption could generate
a huge cloud

reaching tens of miles
into the sky,

pelting the Bay of Naples
with pumice.

Then, when the column collapses,

a massive pyroclastic flow,

heated to hundreds of degrees
Fahrenheit,

would tear across the caldera
at hundreds of miles an hour...

killing everyone in its path

and burying Naples
in an avalanche of ash.

All this area
will be devastating,

and three million of people
will be killed

by the pyroclastic flows.

The people of the Bay of Naples

could suffer the same fate
as the people of Pompeii,

unless they remember
one of the key lessons

of this ancient tragedy:

Those who hunker down
during an eruption

are the ones most likely to die.

If you have a strong eruption,

the only way to save the people
is evacuation.

We need to evacuate,

because it's the only way
we can prevent a disaster,

because there is no way
you can save people

for, from pyroclastic flows.

If evacuation
is the only option,

this will take time
and planning.

In Naples,
millions of people are crammed

into a city of narrow
and crowded streets,

making advanced warning
essential.

One day, there will be
another volcanic eruption,

perhaps even more powerful

than the one
that wiped out Pompeii.

But as scientists improve

their prediction
and early-warning systems,

the next time, there will be
a crucial difference:

They'll know an eruption
is on the way ahead of time,

allowing millions of people
to escape with their lives.

Major funding for "NOVA"
is provided by the following:

To order this "NOVA" program
on DVD,

visit ShopPBS
or call 1-800-PLAY-PBS.

This program is also available
on Amazon Prime Video.