All language subtitles for NOVA.S50E08.Hidden.Volcano.Abyss.1080p.WEB.h264-BAE_track3_[eng]

♪ ♪

(thunder crashing)

NARRATOR:
In January 2022,

the volcano Hunga Tonga-
Hunga Ha'apai

produces the most explosive
eruption ever recorded.

(volcano erupting,
people exclaiming)

MOANA PAEA:
It was so massive!

Threw all of us on the ground!

MAN:
Look, look!

BRANKO SUGAR:
Suddenly, I can see a wall

of white water coming fast.

MAN: Here!
PAEA:
And I just screamed,

"It's a tsunami!"

SUGAR:
Everyone, life jackets!

Get your life jackets!

SUGAR:
I accepted the fact

that we had three minutes
left to live.

(waves crashing,
people crying)

(people exclaiming)

NARRATOR:
Waves as high as 60 feet

devastate the Pacific nation
of Tonga.

Now...

Running away!

NARRATOR:
...a team of scientists
tries to solve

the mysteries of this disaster.

TAANIELA KULA:
This is a turning point

to how we understand the world.

NARRATOR:
Can they reconstruct
the key events...

The wave came from behind
us

and took out these columns.

NARRATOR:
...and answer the critical
question,

could it happen again?

SHANE CRONIN:
Everything that
we've discovered today

is absolutely new,

and I think
will be a quite a shock.

NARRATOR:
"Hidden Volcano Abyss,"
right now, on "NOVA."

♪ ♪

(man speaking on radio)

SUGAR:
We were going spearfishing,
just like we do now.

Me, my son, and the boys.

(man speaking on radio)

The volcano's been erupting
forever.

Every five minutes, for months.

But no big eruption, just...

Just nice ones,
beautiful to see.

We could see it from here.

It was nothing
out of the ordinary.

And then we see the mushroom
was kind of getting bigger.

Look, look!

It just happened in a
couple of minutes, that is...

MAN 2:
How quick it's spreading.
MAN 1: Wow.

So the boys want to stop
and take some photos.

I said, "Ah, yeah, okay."

So I stopped
the boat right here.

♪ ♪

MAN:
Whoo!

(all laughing)

(eruption echoes, men exclaim)

SUGAR:
And suddenly
the explosions came.

(eruptions exploding)

One, two,
boom, bang, bing, bong.

Four, five of them.

I realized
this one is different.

MAN:
Wow!

SUGAR:
And suddenly,

I can see white water from one
end to the next,

as far as you can see.

♪ ♪

A wall of white water.

Nobody think much about it,
but then it hit Fafa Island.

The wave was higher
than the coconut trees.

You couldn't see the island--
nothing.

I knew what was coming.

Tsunami.

I accepted the fact

that we had three
minutes left to live.

I just felt sorry for the boys,

my son and the other boys.

They were busy taking
pictures and laughing.

(men laughing)

SUGAR:
But I knew,

you get hit by tsunami,
you go to deep water.

Just go.

♪ ♪

But the wave is chasing us
and coming fast.

(in video):
Everyone, life jackets!
Get your life jackets!

(present day):
And the sky was gray and murky.

But now we're in the deep water.

We can see the wave come
to the other side

and hit the main island.

It must have gone underneath
us-- we didn't even feel it.

We thought we were now okay,
just go home and that's it.

But the worst was to come.

(rocks, debris splashing)

It start to rain rocks on us.

(in video):
It's getting worse!

(present day):
And then...

(in video):
No!

(present day):
Everything went pitch black.

(debris falling,
water splashing)

You couldn't see
your hand in front of you.

Everything was dark,
no electricity on the island.

No electricity, no lights.

I look at the boys.

Everybody is silent.

Three hours, fighting the sea.

NARRATOR:
Branko and his family had
survived

the most explosive
event ever recorded on Earth.

(eruption explodes)

At 5:15 p.m.
on January 15, 2022,

satellites witnessed the
volcano

Hunga Tonga-Hunga Ha'apai

blast a cloud of ash and
rocks up into the atmosphere.

(eruption echoes,
people shouting)

(water rushing)

NARRATOR:
Within minutes,
tsunami waves crashed

into the South Pacific
nation of Tonga.

(baby crying)

(translated):
I ran with my son.

I could see that the wave
was higher than this house.

(people shouting)

SALOTE KAFOA (translated):
We saw a huge wave.

It came splashing over the top
of the church

and school roofs.

(people exclaiming)

(translated):
A boy came and
reached out to grab me.

I said, "What are you doing?"

He said, "I am going to carry
you, so we can escape."

(woman speaking non-English
language)

(eruption echoes, woman yelps)

NARRATOR:
Rock and debris rained
down on Tonga

for over ten hours...

(debris falling, clanging)
WOMAN:
Jesus Christ.

(child exclaiming in background)

NARRATOR:
...covering the country
in a layer of volcanic dust.

♪ ♪

MARIAN KUPU:
It was a disaster.

It was like driving
through a movie set

where a bomb just exploded.

It was left with dust
and nothing but-- no color.

NARRATOR:
Journalist Marian Kupu

recorded the impact on her
country.

KUPU:
This is my route towards work.

And I would drive here
and I would take pictures.

♪ ♪

There was hopelessness
in the faces of people.

(siren blaring in distance)
People in shock,

calling and looking
for loved ones.

(talking in background)

KUPU:
We didn't know--
are we gonna all die?

Is this the end of the world?

♪ ♪

NARRATOR:
Whole villages were destroyed.

But, remarkably,

across the country, there were
just three deaths.

(explosion echoes)

Scientists around
the world struggled

to explain the enormity
of what had happened.

(rumbling)

CRONIN:
From satellites,
we saw this huge eruption.

We could not believe it.

(rumbling)

And we still don't know what
actually generated that tsunami.

NARRATOR:
Discovering how
Hunga Tonga-Hunga Ha'apai

caused this disaster

could transform our
understanding

of the threats from volcanoes.

(thunder rumbling)

The Kingdom of Tonga.

Home to over 100,000 people.

It is one of the most
isolated countries on Earth.

Separated from
Australia and New Zealand

by hundreds
of miles of open ocean,

it is an archipelago
of over 170 separate islands

in the South Pacific.

♪ ♪

Less than 40 miles from
the main island of Tongatapu

(eruption echoes)

WOMAN:
Oh, my God!

NARRATOR:
When it erupts in January 2022,

the world is in the grip

of the COVID-19 pandemic.

Tonga's borders are closed,

making the nation
even more isolated than usual.

Local scientist Taaniela Kula

is one of the first to respond.

KULA:
As a geologist, I will never
forget this event.

It is the turning point

of how we understand the world.

NARRATOR:
An immediate concern is the
volcanic ash.

Over six million tons
fell on Tongatapu alone...

...transforming
a once-green environment.

(radios running,
sirens blaring in distance)

Tongans mobilize
to begin the cleanup.

But Taaniela fears
the ash poses a danger

to human health.

KULA:
Rainwater is our source of
drinking water,

and volcanic ash,
when it interacts with water,

makes the water more acidic,
so it causes health problems.

So we started
collecting the ash,

so that we know
the true contamination level.

(radio running)

NARRATOR:
Samples reveal the ash
isn't toxic.

And Tongans can start
rebuilding their lives.

For Taaniela, mysteries remain.

Why did the volcano
suddenly erupt so violently?

And is it still
a danger to his country?

To find out, he needs equipment
and resources from overseas.

Nine months after the eruption,
he gets his opportunity.

(metal clanging)

The COVID restrictions
have been relaxed.

Tonga's borders have
reopened.

And an international team
of scientists

can join Taaniela on an
expedition

to the Hunga volcano.

KULA:
People are still anxious to know
what's the status at this point.

It's our responsibility to make
sure we know our environment

and what's the risk.

NARRATOR:
On the ship are marine
geologist Marta Ribó

and a volcanologist
who has spent decades studying

the volcanoes
of the South Pacific...

That one just needs to be
parallel with this one.

NARRATOR:
...Shane Cronin.

CRONIN:
That's it.

CRONIN:
I've been working with Taaniela
for the last 20 years or so...

All right!

...to understand just
how these volcanoes work.

Let's rock!

(calls out)

Ooh, I feel we're moving.

Hunga is one of these typical
volcanoes that sort of

puffed away for a long time--
so in this case, decades--

just producing these small
eruptions,

and then there was
this incredibly big eruption.

This was generated by something
at the volcano,

we just don't know what.

NARRATOR:
Ahead of them
lies a five-hour voyage

to one of the most geologically
active places on Earth.

♪ ♪

To the east of Tonga,

two of the planet's vast
tectonic plates

are crashing into each other.

The Pacific Plate is
being forced downwards,

in a process called subduction.

As it descends towards
the hot center of the Earth,

it gets warmer.

The rocks begin to melt,
turning into liquid magma,

which rises towards the surface,

collecting in magma chambers
under the sea floor.

Occasionally,
this magma surges upwards...

...and erupts out of the
volcano.

But the constant subduction
refills the magma chamber.

Which can trigger more
eruptions.

♪ ♪

40 miles from Tongatapu,

the ship reaches
an area of open ocean.

This is the site of the
volcano.

All that is visible
are two small islands,

Hunga Tonga

and Hunga Ha'apai.

Looking behind me, you'll see,

seeing the island of Hunga
Ha'apai.

So that's right on
the edge of the volcano.

The main volcano is
actually over to the east.

So in this great
big expanse of what looks

just like
completely clear ocean,

we're actually sitting right
on top of the Hunga caldera.

So below us
is actually the volcano.

NARRATOR:
Hunga Tonga-Hunga Ha'apai
is a submarine volcano.

Its two-and-a-half-mile-wide
crater

sits at the top of a mountain
nearly 6,000 feet tall,

which is almost
completely hidden underwater.

Only in two places is
the crater wall high enough

to break the surface,

forming the two islands.

Before the January 15 eruption,

the volcano
looked very different.

The center of the crater was
2,300 feet shallower.

The islands were far bigger,

and between them was the
volcanic cone.

(eruptions rumbling)

On December 20, 2021, this
cone suddenly sprang to life.

Usually, eruptions in Tonga
are monitored by satellite,

but space is too far
away to pick up all the detail.

(man speaking
non-English language)

NARRATOR:
So, for almost four weeks,

Taaniela regularly came
to the volcano

to check for increasing
activity with a drone.

(eruption echoes)

KULA:
We came here on

the evening of the 14th
of January.

I saw a column of ash and gas...

...almost two miles wide

just rising into the heavens.

(thunder rumbling)

There were
lightning bolts everywhere.

It happened
all around the island.

(thunder rumbling)

It's like shooting several
thousands of crack, firecrackers

all at the same time.

(eruption exploding)

It felt like I'm
witnessing Mother Earth's might

and power being released.

(thunder crashing)

NARRATOR:
Eight hours later,
the volcano stopped erupting.

Then, at 5:15 p.m.
on January 15...

...it produced an eruption over
70 times larger...

...exploding with the power of
over 60 million tons of TNT

and triggering
a series of tsunami waves

that hit Tonga, Australia,

Japan, and the Americas.

Why had this volcano suddenly
produced

such an immense explosion?

Why was it so much more powerful

than the previous day's
eruption?

And is the volcano active enough

to erupt again in the near
future?

First, the team needs to know
the volcano's current activity.

CRONIN (chuckling):
The weather's not ideal.

I mean, the big problem
for us is,

is the sea condition,

and a strong wind is on its way.

So we're really hoping

that we can get all the survey
done

before that, that starts coming
on.

(radio running)

NARRATOR:
Marta is trying to gauge the
volcano's activity using sonar.

(pinging faintly)

The echo sounder
is sending a ping down,

and the reflection of
that ping noise,

of the sea floor.

NARRATOR:
The scanning will reveal
if magma is dangerously close

to the surface.

♪ ♪

(people talking and laughing
in background)

Wow, these are, it's stronger
than the one before.

CRONIN:
So these are
the shallow ones...

NARRATOR:
Escaping from the sea floor
are plumes of volcanic gases

released by the magma.

1,340 meters.

NARRATOR:
The closer the magma
is to the surface,

the hotter the plumes

and the more likely an eruption.

(talking in background)

CRONIN:
This is a sensor,
which actually measures,

2,000 times a second,
the temperature of the water.

Is the volcano
heating the water, for example?

Is the volcano changing
the water temperature?

It's all the question of whether
the volcano is alive or not.

That's it, that's it, that's it!

RIBÓ:
Careful.

CRONIN:
Down, down, down, quick.

Keep going, yup.

NARRATOR:
Measuring multiple plumes will
reveal how close

the volcano is to erupting.

Running away!

KULA:
It's a big one!

NARRATOR:
They see a consistent trend.

RIBÓ:
All of the plumes,
they're very weak.

NARRATOR:
The plumes aren't hot.

RIBÓ:
It's still active,

but the strength of the volcano
has decreased.

So for the people of Tonga,
there is still some risk,

but it's less dangerous.

NARRATOR:
The team's findings
suggest the Hunga volcano

won't produce another massive
eruption--

for the time being.

But the events of January 15

show this is
an unpredictable volcano.

Why did it suddenly
produce an eruption

70 times bigger
than the previous day?

It's a question
with global implications.

There could be as many
as 50,000 submarine volcanoes

lurking under
our planet's waves.

In recent years, Kolumbo,

near the Greek island of
Santorini,

and Oomurodashi, less than 40
miles from the center of Tokyo,

have been identified
as active threats.

Knowing exactly how the Hunga
volcano generated

such a powerful eruption

could change our understanding

of the dangers from
submarine volcanoes.

(debris falling,
people shouting)

And the clues

could lie in the ash
Hunga Tonga-Hunga Ha'apai

rained down on the islands.

♪ ♪

The debris contains
time capsules from the eruption,

which volcanologist
Joali Paredes-Mariño analyzes.

The first thing that highlights,
to, to me, is this very dark

and, like, glossy,

blocky particles--
so, that's glass.

NARRATOR:
Volcanic glass
is solidified magma,

created at the very moment
the volcano exploded.

A powerful electron microscope

allows Joali to compare
different samples of glass.

This one's
from a different eruption.

We got this kind of, like,
massive glass,

covered with bubbles.
MAN:
Right.

NARRATOR:
Explosions happen when a
material expands very rapidly.

In most eruptions, this material

is gas in the magma.

Normally, this gas is dissolved
in the liquid magma,

just like in a soda.

If some reason, the pressure
that is on that magma change,

like when you open
a bottle of soda,

you will have all these bubbles.

They will create this inner
force that, at the moment

that it cannot
hold it any longer,

it will fragment the magma.

And that's what creates
an eruption from within.

NARRATOR:
The growing bubbles of gas
inside the magma

cause it to expand rapidly
and explode,

and are clearly visible in
glass from a typical eruption.

But the team sees
something very different

in this sample
from the Hunga volcano.

If we see the one in the center,
you don't see those bubbles.

They have kind of blocky
particles.

NARRATOR:
No bubbles means the
eruption wasn't generated

by the sudden expansion of gas
in the magma.

The shapes of the fragments
point to the explosion

of a completely different
material.

You have this
kind of, like, step fractures.

And also, you can see

the big particle
in the bottom corner.

This is concave fractures.

NARRATOR:
This pattern
of fractures is consistent

with a very
specific explosive event.

That means that is telling
us this is interaction

with magma and water.

NARRATOR:
Water can be extremely
explosive.

If it hits
something as hot as magma,

water instantly turns to gas,

expanding as much as 4,000
times.

(thunder crashing)

It would seem
the most intense eruption

ever witnessed by science

was detonated by the explosion
of water.

♪ ♪

But there is a mystery.

The volcano's magma is usually
locked away from the ocean,

in a chamber over
three miles below the surface.

Why did water and
magma suddenly come into contact

on January 15?

In the global seismic records,

the team spots signals
the satellites didn't detect.

Okay.
That's it?

Uh-huh!
Yes.

NARRATOR:
28 minutes before the big
eruption,

there was a series of smaller,
precursory eruptions.

CRONIN:
We think the precursory
eruptions

led to the rapid fracturing
of the upper volcano.

and we start a very,
very violent explosion.

NARRATOR:
The magma and water

were separated by thousands
of feet of solid rock.

The team thinks,
on January 15,

the first of the precursory
eruptions cracked open faults.

As this series of eruptions
continued,

these cracks grew bigger.

And bigger.

Until finally, they allowed
cold seawater to flood in,

hitting incredibly hot magma
in the chamber

and generating
the immense explosion.

(booming)

The investigators have made
a major breakthrough:

an explanation for
how the Hunga volcano

could have produced
such a powerful explosion.

But they
face another problem.

(eruption explodes,
thunder crashes)

Most tsunamis are
caused by earthquakes.

Volcanic tsunamis are so rare,

scientists don't know
how the Hunga volcano

generated a series
of enormous waves.

Discovering what happened here
could give new insights

into the global threat
from submarine volcanoes.

The answers could lie
on Tonga's Hihifo peninsula.

Once, this area was dotted
with thriving resorts.

One of the busiest
was owned by Moana Paea.

PAEA:
The whole place

was just full of beautiful
big trees

and coconut trees
and palm trees.

That used to be the tree
with all surfboards on it.

It was a massive tree.

As a kid,
we would climb around it.

But after that tree,
there was a house there,

and then from there
would be the beach area.

NARRATOR:
The Hihifo peninsula lies

on the northwest coast of
Tongatapu.

Less than 40 miles due north

is the volcano
Hunga Tonga-Hunga Ha'apai.

(volcano rumbling,
thunder crashing)

PAEA:
The volcano was going crazy,
striking lightning and stuff.

Because it'd been happening
for weeks and weeks,

we kind of took it for granted
that it must be all right.

♪ ♪

We had a full hotel,

and maybe quarter past five,
I heard screaming.

MAN:
Here!

PAEA:
One of my staff said,

"Hey, look at the water."

It looked like
a washing machine.

(man exclaims)

And I just screamed,
"It's a tsunami!"

(people yelling in background)

PAEA:
And people were going to
pack their clothes,

and I said,
"No, you need to get out!"

One family literally
just got out of the pool

and got in their car
and took off.

(men speaking indistinctly)

PAEA:
That's when I saw...

MAN:
Oh, my God.

PAEA:
...the water is moving fast,
but growing.

So we ran through here.

(people exclaiming)
WOMAN: Oh! Oh, (bleep)!

PAEA:
We were yelling,
"Tsunami! Tsunami!"

MAN:
Holy (bleep)!

(people exclaiming)

PAEA:
And my son was, like,

"Mom, let's climb a tree."

And then, suddenly...

(explosion pounds)

MAN:
Oh, (bleep)!

WOMAN:
Whoa!

MAN:
Holy (bleep)!

PAEA:
Another massive explosion.

MAN:
Tsunami's heading in.

(people exclaiming)
(bleep)

The pressure of it
threw all of us on the ground.

My daughter
was crying, "My ears!"

But my sons are, like,
"Mom, get up, get up!"

Because we could still hear
waves rumbling.

(men shouting indistinctly)

MAN:
Okay, okay!

(baby crying)

(man panting)

MAN:
Here!

(waves crashing, water rushing)

PAEA:
And when we got down
to the road,

there's this
two-story house there,

and there were all
these village people

up on top of there,
and it started to

rain down with dust.

(baby crying,
people murmuring and exclaiming)

(water rushing)

PAEA:
When we got to the roof,

we saw the big swell
coming across.

(people whimpering and shouting)

PAEA:
We were praying and singing.

And then my brother came,
so we all came down.

(water rushing)

We got in the car,
and it being so dark,

and the dust was massive,
and rocks coming...

(debris pelting)
CHILD:
Mommy...

PAEA: And they weren't
just little rocks.
(debris pelting)

(people whimpering, murmuring)

♪ ♪

(people speaking in background)

NARRATOR:
Like many Tongans,

Moana headed for
the safety of high ground.

♪ ♪

The next day revealed
the scale of the destruction.

♪ ♪

PAEA:
I remember one of my staff
ringing up the next morning.

(voice breaking):
And he's saying, "Sorry, Moana,

everything is gone."

And I said to him,
"Praise God,

"we are all still alive.

That's the main thing."
(sniffs)

(breath trembles)

♪ ♪

We loved it here.

Such a beautiful space.

(gasps)

It was very hard to see,

because this is our livelihood,

and this is something
that has looked after...

(sniffles):
...our community for many years.

(sniffles, breathes deeply)

♪ ♪

NARRATOR:
Ahead of Moana lies months
of rebuilding.

This is the stark reality
of the tsunami that hit Tonga.

But this event
is also a mystery.

How did the volcano generate
such destructive waves?

Tsunami scientist Jose Borrero
has flown in to investigate.

(wind blowing)

(shutter clicking)

BORRERO:
As tsunami waves
propagate through the ocean,

their speed is governed
by the depth of the water.

So, the deeper the water,
the faster they can go.

Now, where we are,
on the west coast of Tongatapu,

there was a very narrow
fringing reef,

and you can see the reef here.

It was where
the waves are breaking.

the water drops off to
about a depth of

just over 1,000 meters.

It's deep water from here
out to the Hunga volcano.

♪ ♪

The tsunami came
directly in here, unimpeded.

There was no reefs
or features

or anything in the way
to slow it down, redirect it.

♪ ♪

And the tsunami
takes only eight minutes

to get from the volcano
to here.

♪ ♪

NARRATOR:
A wave with immense power
arrived at the peninsula

and caused widespread damage

because of what happens when
a tsunami enters shallow water.

♪ ♪

The energy of a tsunami
is spread throughout

the depth of the ocean.

In deep water,

this makes the height
of the wave barely noticeable.

But as the wave reaches
shallow water,

it is slowed dramatically,

and the water begins
to pile up,

making the wave
higher and higher.

BORRERO:
When a tsunami comes ashore,

it's not just the water
that causes the damage.

It starts to pick things up.

It starts with boulders
and sand.

And then it knocks down trees,

and the trees become
entrained in the flow.

Then it'll take out a house,

and the material from the house
will become part of the flow.

And all of this material
gradually builds up

until it's, it's not even water
anymore.

It's a dense debris flow

of everything that the wave
has picked up along the way.

♪ ♪

NARRATOR:
Jose's first task is working out
the height and power

of the incoming wave.

And the trail of destruction
offers him the vital clues.

This is weird.

very difficult
to bend with your hand,

but the way we see it here,

just wrapped around
a concrete pillar

like tissue paper,
but with roofing steel.

NARRATOR:
First, Jose needs to find
the wave's direction.

Over here,

we see these
concrete columns

are knocked down in the
direction the wave was going.

So the wave came from
behind us,

from the north,
swept down the beach,

and took out these columns,
laying them down that way.

NARRATOR:
Following the trail of debris
inland,

Jose can find
the evidence he needs.

♪ ♪

BORRERO:
Up here is one of the most
crucial bits of information

from the whole tsunami event.

This was a cell phone tower.

And on the cell phone tower
was a weather station,

and, as you can see,
was completely obliterated

by the tsunami surge.

This is a very
strong piece of equipment.

It's a big, strong thing.

This was
a 20-meter-tall tower.

But yet the force was able
to bend the entire thing over.

And 200 meters inland,
on one of the trees

is pieces of this tower
still hanging from a branch

five to six meters
above the ground.

NARRATOR:
Bringing all of this
information together,

Jose can compute
the scale of the tsunami.

♪ ♪

BORRERO:
So the ground level
that we're standing at

is about 13 meters
above sea level.

And then with the flow marks
around this area,

we know that the tsunami
flow depth through here was

somewhere to
five to six meters.

So we're talking,
you know, 18, 19 meters

of, of total tsunami height
passing through this area.

NARRATOR:
19 meters is over 60 feet--

about the height
of a six-story building.

(water rushing)

NARRATOR:
In 2011, a massive earthquake
unleashed a tsunami on Japan.

(people screaming)

NARRATOR:
Despite being protected by
a breakwater

costing some $1.6 billion,

Kamaishi City
was hit by a wave

that measured 26 feet tall.

(water rushing)

All of this damage
was caused by a wave

less than half the height
of the Hihifo tsunami.

♪ ♪

How did the Hunga volcano
generate such an immense wave?

(men exclaiming)

BORRERO:
So, yeah, this is you guys

parked up here.
Yes.

NARRATOR:
To find out,

Jose gathers eyewitness
testimony and video.

MAN 2:
I was the driver of that car.

BORRERO: Were you waiting for
someone to come?
No.

We were waiting
because the...

The road! Over the road.
The road was busy.

(laughs):
And the waves
began banging on the car.

(all exclaiming in video)

(video rewinding)

NARRATOR:
Jose is combining
this firsthand evidence

with images and videos
he has found on social media.

BORRERO:
It's astounding,

the amount of material
that's available online.

People just post things up,

and all of this
is completely useful

in a scientific sense.

We have a set of videos

that show a series
of tsunami waves,

and we know what time
the video was taken.

And by knowing the timing
of when it's hitting the coast,

it gives us clues as to

how that wave was generated
at the volcano.

NARRATOR:
Jose has built
a timeline of the day.

(eruption explodes in distance)
MAN 1: Oh! MAN 2: Whoo!

MAN 1:
Holy (bleep)!

NARRATOR:
He's identified not one,
but two tsunamis--

one at 5:23
and one at 5:34.

(mouse clicking)

Tracking back
eight minutes from each,

he finds the same thing.

An eruption at the volcano.

♪ ♪

This fits with one theory

of how submarine volcanoes
produce tsunamis.

As material erupts upwards,
it pushes water out of the way,

creating immense waves that
radiate out from the volcano.

But Jose doesn't think
these eruptions

can explain the destructive
60-foot-high tsunami.

♪ ♪

BORRERO:
We know the weather station

transmitted its last packet
of data at 6:00 p.m.

So we know a tsunami

could not have destroyed
the weather station

and the cell phone tower
that it was attached to

until sometime after 6:00 p.m.

This means that
there was a later wave.

But this doesn't fit

with the idea that
the wave was generated

during these two
volcanic eruptions.

♪ ♪

NARRATOR:
If it wasn't an eruption,

what other event
at the Hunga volcano

would have enough power
to unleash

a 60-foot-high tsunami?

(eruption thundering)

(roaring)

One possibility lies with
the speed it threw out material.

CRONIN:
During the first
one-and-a-half hours,

it was ejecting material
at a rate twice as much as

the next-biggest eruption
that we know of.

It threw out
seven cubic kilometers of

dense rock material.

NARRATOR:
That's enough to cover
the entire island of Manhattan

in nearly
400 feet of debris.

CRONIN:
When a large amount of magma
erupts from a volcano,

large amounts of magma
come out at once.

And so that means that
the top part of the volcano

actually then
sinks in on itself.

NARRATOR:
Shane's idea is that

as material erupted out
of the magma chamber,

it created a larger and larger
void underground.

When it could no longer support
the weight of material above,

the entire caldera dropped
over 2,300 feet.

Seawater flooded in,

kickstarting tsunamis
that radiated

out from the volcano,

an explanation
of how the volcano

could generate
a 60-foot wave.

♪ ♪

The team has found
that a caldera

where the water can
get into the magma chamber

can erupt explosively

and generate
life-threatening tsunamis,

heightening the need to monitor
these types of volcanoes.

And only 55 miles from
Hunga Tonga-Hunga Ha'apai

is its volcanic twin:

the island of Tofua.

Just like the Hunga volcano,

Tofua has a two-and-a-half-
mile-wide caldera.

But its magma chamber
is far closer to the surface,

and far closer to
the surrounding seawater.

♪ ♪

KULA:
Captain,

we're keeping
a straight line.

We're about here.

CRONIN:
It's a very remote part
of the world,

and so no one's been able
to get here.

It's 14 hours on the boat,

and out here,
the ocean can be

extremely treacherous.

♪ ♪

All previous measurements

have been made
from satellite observations,

so it's critical that we try
to land on the island.

NARRATOR:
The satellites suggest

there is virtually no activity
at Tofua.

But this has never been verified
with field measurements.

NARRATOR:
Taaniela and Shane
enlist the help of boatmen

from the neighboring island
of Kotu.

(motor humming)

They report having seen

a red glow
above Tofua at night.

♪ ♪

KULA:
I feel excited to go up
for the first time.

We hope to get some real data
on the ground.

And then, uh,
we can share it with the world.

♪ ♪

NARRATOR:
First, they need to ascend

over 1,500 feet
through tropical forests.

♪ ♪

CRONIN:
It's quite humid.

So...

I think my sweat is
on top of my sweat,

building up
a third layer of sweat.

(grunts)

♪ ♪

NARRATOR:
Their first objective:

the rim of Tofua's
two-and-a-half-mile-wide crater.

CRONIN:
Look, look, this is
a big caldera.

Yeah,
so there's the active cone.

That's our destination,
should we decide to accept it.

NARRATOR:
Shane suspects the satellites
are wrong

and Tofua could be due an
eruption.

CRONIN:
We had a big eruption around
1,200 years ago,

another big one
around 800 years ago,

and the most recent one
around 400 years ago.

NARRATOR:
This pattern suggests
Tofua should erupt again,

and soon.

(camera shutter clicks)

CRONIN:
Okay, it's fantastic.

We've got a bit of a break
in the weather.

You can see how blue that gas is
coming off that volcano.

When the color of the gas
is blue, it's sulfur dioxide.

NARRATOR:
This gas is released by
the magma.

The blue color
is only visible

if the levels of sulfur dioxide
are high.

CRONIN:
So I think the magma

must be very close to the...
(shutter clicks)

...close to the surface,
actually.

(shutter clicks)

And this corresponds to

what the locals
have been reporting

over the last
couple of months,

is that there is
a glow in the sky above Tofua

when there's a cloudy evening.

NARRATOR:
The signs point to Tofua being
far more active

than the satellite readings
suggest.

But to know the level
of the threat,

the team needs more evidence.

Taaniela will use a drone
to investigate the active cone.

While the rest of the team
will collect vital readings,

which need to be taken
from inside the caldera itself.

♪ ♪

CRONIN:
I'm going to try and get
a position close to the plume.

I don't want to go
underneath it,

because sulfur dioxide is
actually quite lethal.

We can then try to measure
some of the output.

This is what I've been
lugging up the hill.

NARRATOR:
Volcanologists monitor
the sulfur dioxide

to gauge the activity
of volcanoes.

CRONIN:
This is the telescope.

And it's a rotating one.

NARRATOR:
The more sulfur dioxide

Shane detects,
the more active

the volcano.

Now...

It's going to be scanning
over there,

and I want it to scan
above the level

of the
opposite caldera rim.

We're capturing it
beautifully with this angle.

♪ ♪

NARRATOR:
Shane's readings indicate
the satellites have been

dangerously underestimating
the levels of sulfur dioxide.

Tofua is releasing far more
than previously thought.

♪ ♪

Taaniela's expert flying
reveals that

the magma has
welled up in the crater,

creating a lava lake,

one of fewer than ten
on the entire planet.

And there's a sign Tofua has
been actively throwing out lava,

incredibly recently.

CRONIN:
This erupted in the last
few days.

It's a fresh volcanic bomb.

So this really contrasts to

all of the rest of
the older material around here.

So there's been some quite
big explosions to produce these.

It's really interesting,
because it looks as if

Tofua is entering
a new phase of activity,

one that we haven't
seen here before.

♪ ♪

Everything that we've
discovered today

is absolutely new,
and I think will be

quite a shock
around the globe.

NARRATOR:
Tonga is still recovering

from the eruption of
the Hunga volcano.

Now
scientists have discovered

that its volcanic twin,
Tofua,

is far more active

than satellites have
led them to believe,

a finding that has implications
far beyond Tonga.

♪ ♪

KULA:
Our latest expedition
really showed us

there are limitations
of the satellite system.

You always need to be on-site
to actually know

the full level of
the volcanic activity.

NARRATOR:
With as many as 50,000 submarine
volcanoes around the planet,

the world needs
to find better ways of

keeping an eye on these
destructive forces of nature.

♪ ♪

And be ready

for the next
Hunga Tonga-Hunga Ha'apai.

(people exclaiming)

(speaking Tongan):

NARRATOR:
Taaniela and his colleagues

have long reached out to
people of Tonga.

ANA MAEA
(speaking Tongan):

PUPILS:

KULA:
We feel that it's our
responsibility

to build awareness about
geological hazards and risks

that we are exposed to.

NARRATOR:
It's a strategy that

the rest of the world
could learn from.

MAEA:

NARRATOR:
Awareness is a major reason

just three people died in Tonga

during
the Hunga volcano disaster.

BORRERO:
The death toll was so low

because of the knowledge
of tsunami.

Everybody moved to high ground,

they alerted their neighbors,

they alerted their friends,
and everybody evacuated.

It's miraculous,

but it's doing the right thing
at the right time.

♪ ♪

KULA:
Our existence today is

a demonstration of
our resilience.

♪ ♪

And I think knowledge
will increase the resilience

of the people in the world.

(crowd cheering)

NARRATOR:
Being ready

is Tonga's lesson
for the rest of the planet.

(cheering)

♪ ♪

♪ ♪

♪ ♪

♪ ♪

♪ ♪