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♪ ♪

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(thunder crashing)

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NARRATOR:
In January 2022,

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the volcano Hunga Tonga-
Hunga Ha'apai

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produces the most explosive
eruption ever recorded.

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(volcano erupting,
people exclaiming)

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MOANA PAEA:
It was so massive!

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Threw all of us on the ground!

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MAN:
Look, look!

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BRANKO SUGAR:
Suddenly, I can see a wall

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of white water coming fast.

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MAN: Here!
PAEA:
And I just screamed,

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"It's a tsunami!"

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SUGAR:
Everyone, life jackets!

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Get your life jackets!

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SUGAR:
I accepted the fact

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that we had three minutes
left to live.

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(waves crashing,
people crying)

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(people exclaiming)

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NARRATOR:
Waves as high as 60 feet

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devastate the Pacific nation
of Tonga.

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Now...

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Running away!

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

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the mysteries of this disaster.

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TAANIELA KULA:
This is a turning point

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to how we understand the world.

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NARRATOR:
Can they reconstruct
the key events...

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The wave came from behind
us

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and took out these columns.

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NARRATOR:
...and answer the critical
question,

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could it happen again?

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SHANE CRONIN:
Everything that
we've discovered today

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is absolutely new,

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and I think
will be a quite a shock.

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

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♪ ♪

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(man speaking on radio)

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

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Me, my son, and the boys.

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(man speaking on radio)

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The volcano's been erupting
forever.

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Every five minutes, for months.

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But no big eruption, just...

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Just nice ones,
beautiful to see.

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We could see it from here.

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It was nothing
out of the ordinary.

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

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Look, look!

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

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

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So the boys want to stop
and take some photos.

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I said, "Ah, yeah, okay."

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So I stopped
the boat right here.

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♪ ♪

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MAN:
Whoo!

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(all laughing)

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(eruption echoes, men exclaim)

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SUGAR:
And suddenly
the explosions came.

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(eruptions exploding)

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

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Four, five of them.

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I realized
this one is different.

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MAN:
Wow!

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SUGAR:
And suddenly,

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

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as far as you can see.

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♪ ♪

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A wall of white water.

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

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The wave was higher
than the coconut trees.

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You couldn't see the island--
nothing.

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I knew what was coming.

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Tsunami.

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I accepted the fact

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that we had three
minutes left to live.

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I just felt sorry for the boys,

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my son and the other boys.

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They were busy taking
pictures and laughing.

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(men laughing)

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SUGAR:
But I knew,

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

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Just go.

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♪ ♪

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But the wave is chasing us
and coming fast.

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

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

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But now we're in the deep water.

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We can see the wave come
to the other side

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and hit the main island.

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

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

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But the worst was to come.

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(rocks, debris splashing)

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It start to rain rocks on us.

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(in video):
It's getting worse!

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(present day):
And then...

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(in video):
No!

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(present day):
Everything went pitch black.

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(debris falling,
water splashing)

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

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Everything was dark,
no electricity on the island.

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No electricity, no lights.

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I look at the boys.

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Everybody is silent.

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Three hours, fighting the sea.

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NARRATOR:
Branko and his family had
survived

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the most explosive
event ever recorded on Earth.

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(eruption explodes)

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

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satellites witnessed the
volcano

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Hunga Tonga-Hunga Ha'apai

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

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(eruption echoes,
people shouting)

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(water rushing)

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NARRATOR:
Within minutes,
tsunami waves crashed

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into the South Pacific
nation of Tonga.

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(baby crying)

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(translated):
I ran with my son.

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

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(people shouting)

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

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It came splashing over the top
of the church

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and school roofs.

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(people exclaiming)

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

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I said, "What are you doing?"

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

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(woman speaking non-English
language)

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(eruption echoes, woman yelps)

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NARRATOR:
Rock and debris rained
down on Tonga

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for over ten hours...

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(debris falling, clanging)
WOMAN:
Jesus Christ.

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(child exclaiming in background)

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

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♪ ♪

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MARIAN KUPU:
It was a disaster.

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It was like driving
through a movie set

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where a bomb just exploded.

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

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It was just like
a black-and-white movie.

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NARRATOR:
Journalist Marian Kupu

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recorded the impact on her
country.

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KUPU:
This is my route towards work.

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And I would drive here
and I would take pictures.

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♪ ♪

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There was hopelessness
in the faces of people.

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(siren blaring in distance)
People in shock,

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calling and looking
for loved ones.

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(talking in background)

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

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Is this the end of the world?

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♪ ♪

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NARRATOR:
Whole villages were destroyed.

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But, remarkably,

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across the country, there were
just three deaths.

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(explosion echoes)

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Scientists around
the world struggled

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to explain the enormity
of what had happened.

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(rumbling)

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CRONIN:
From satellites,
we saw this huge eruption.

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We could not believe it.

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(rumbling)

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

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NARRATOR:
Discovering how
Hunga Tonga-Hunga Ha'apai

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caused this disaster

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could transform our
understanding

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of the threats from volcanoes.

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(thunder rumbling)

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The Kingdom of Tonga.

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Home to over 100,000 people.

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It is one of the most
isolated countries on Earth.

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Separated from
Australia and New Zealand

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by hundreds
of miles of open ocean,

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it is an archipelago
of over 170 separate islands

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in the South Pacific.

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♪ ♪

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Less than 40 miles from
the main island of Tongatapu

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is the volcano
Hunga Tonga-Hunga Ha'apai.

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(eruption echoes)

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WOMAN:
Oh, my God!

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NARRATOR:
When it erupts in January 2022,

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the world is in the grip

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of the COVID-19 pandemic.

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Tonga's borders are closed,

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making the nation
even more isolated than usual.

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Local scientist Taaniela Kula

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is one of the first to respond.

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

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It is the turning point

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of how we understand the world.

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NARRATOR:
An immediate concern is the
volcanic ash.

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Over six million tons
fell on Tongatapu alone...

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...transforming
a once-green environment.

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(radios running,
sirens blaring in distance)

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Tongans mobilize
to begin the cleanup.

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But Taaniela fears
the ash poses a danger

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to human health.

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KULA:
Rainwater is our source of
drinking water,

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and volcanic ash,
when it interacts with water,

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

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So we started
collecting the ash,

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so that we know
the true contamination level.

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(radio running)

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00:11:05,600 --> 00:11:10,000
NARRATOR:
Samples reveal the ash
isn't toxic.

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And Tongans can start
rebuilding their lives.

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For Taaniela, mysteries remain.

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Why did the volcano
suddenly erupt so violently?

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And is it still
a danger to his country?

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

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Nine months after the eruption,
he gets his opportunity.

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(metal clanging)

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The COVID restrictions
have been relaxed.

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Tonga's borders have
reopened.

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And an international team
of scientists

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can join Taaniela on an
expedition

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00:12:01,700 --> 00:12:04,033
to the Hunga volcano.

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

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00:12:07,933 --> 00:12:12,933
It's our responsibility to make
sure we know our environment

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00:12:12,933 --> 00:12:16,566
and what's the risk.

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NARRATOR:
On the ship are marine
geologist Marta Ribó

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00:12:21,566 --> 00:12:24,833
and a volcanologist
who has spent decades studying

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00:12:24,833 --> 00:12:26,500
the volcanoes
of the South Pacific...

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That one just needs to be
parallel with this one.

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NARRATOR:
...Shane Cronin.

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CRONIN:
That's it.

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00:12:32,933 --> 00:12:35,600
CRONIN:
I've been working with Taaniela
for the last 20 years or so...

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All right!

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...to understand just
how these volcanoes work.

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Let's rock!

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00:12:41,933 --> 00:12:44,133
(calls out)

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00:12:45,566 --> 00:12:47,966
Ooh, I feel we're moving.

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Hunga is one of these typical
volcanoes that sort of

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

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just producing these small
eruptions,

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and then there was
this incredibly big eruption.

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This was generated by something
at the volcano,

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00:13:02,966 --> 00:13:05,066
we just don't know what.

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00:13:06,300 --> 00:13:09,533
NARRATOR:
Ahead of them
lies a five-hour voyage

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00:13:09,533 --> 00:13:13,833
to one of the most geologically
active places on Earth.

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♪ ♪

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00:13:19,733 --> 00:13:21,633
To the east of Tonga,

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two of the planet's vast
tectonic plates

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are crashing into each other.

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00:13:26,766 --> 00:13:29,833
The Pacific Plate is
being forced downwards,

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00:13:29,833 --> 00:13:32,700
in a process called subduction.

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00:13:34,266 --> 00:13:37,300
As it descends towards
the hot center of the Earth,

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00:13:37,300 --> 00:13:39,733
it gets warmer.

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The rocks begin to melt,
turning into liquid magma,

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00:13:44,566 --> 00:13:47,200
which rises towards the surface,

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00:13:47,200 --> 00:13:52,000
collecting in magma chambers
under the sea floor.

252
00:13:52,000 --> 00:13:55,566
Occasionally,
this magma surges upwards...

253
00:13:57,300 --> 00:14:00,366
...and erupts out of the
volcano.

254
00:14:00,366 --> 00:14:04,933
But the constant subduction
refills the magma chamber.

255
00:14:04,933 --> 00:14:09,466
Which can trigger more
eruptions.

256
00:14:09,466 --> 00:14:11,666
♪ ♪

257
00:14:11,666 --> 00:14:14,333
40 miles from Tongatapu,

258
00:14:14,333 --> 00:14:18,600
the ship reaches
an area of open ocean.

259
00:14:18,600 --> 00:14:23,066
This is the site of the
volcano.

260
00:14:23,066 --> 00:14:26,433
All that is visible
are two small islands,

261
00:14:26,433 --> 00:14:28,300
Hunga Tonga

262
00:14:28,300 --> 00:14:31,600
and Hunga Ha'apai.

263
00:14:31,600 --> 00:14:33,800
Looking behind me, you'll see,

264
00:14:33,800 --> 00:14:36,000
seeing the island of Hunga
Ha'apai.

265
00:14:36,000 --> 00:14:38,933
So that's right on
the edge of the volcano.

266
00:14:38,933 --> 00:14:42,033
The main volcano is
actually over to the east.

267
00:14:42,033 --> 00:14:44,533
So in this great
big expanse of what looks

268
00:14:44,533 --> 00:14:46,966
just like
completely clear ocean,

269
00:14:46,966 --> 00:14:51,100
we're actually sitting right
on top of the Hunga caldera.

270
00:14:51,100 --> 00:14:54,600
So below us
is actually the volcano.

271
00:14:56,833 --> 00:15:01,300
NARRATOR:
Hunga Tonga-Hunga Ha'apai
is a submarine volcano.

272
00:15:03,000 --> 00:15:05,100
Its two-and-a-half-mile-wide
crater

273
00:15:05,100 --> 00:15:10,533
sits at the top of a mountain
nearly 6,000 feet tall,

274
00:15:10,533 --> 00:15:13,766
which is almost
completely hidden underwater.

275
00:15:15,800 --> 00:15:18,666
Only in two places is
the crater wall high enough

276
00:15:18,666 --> 00:15:20,600
to break the surface,

277
00:15:20,600 --> 00:15:24,966
forming the two islands.

278
00:15:24,966 --> 00:15:28,000
Before the January 15 eruption,

279
00:15:28,000 --> 00:15:30,866
the volcano
looked very different.

280
00:15:32,733 --> 00:15:37,733
The center of the crater was
2,300 feet shallower.

281
00:15:39,133 --> 00:15:42,266
The islands were far bigger,

282
00:15:42,266 --> 00:15:45,766
and between them was the
volcanic cone.

283
00:15:45,766 --> 00:15:49,066
(eruptions rumbling)

284
00:15:49,066 --> 00:15:54,066
On December 20, 2021, this
cone suddenly sprang to life.

285
00:15:56,866 --> 00:16:01,833
Usually, eruptions in Tonga
are monitored by satellite,

286
00:16:01,833 --> 00:16:06,333
but space is too far
away to pick up all the detail.

287
00:16:07,500 --> 00:16:08,533
(man speaking
non-English language)

288
00:16:09,833 --> 00:16:11,666
NARRATOR:
So, for almost four weeks,

289
00:16:11,666 --> 00:16:13,933
Taaniela regularly came
to the volcano

290
00:16:13,933 --> 00:16:18,833
to check for increasing
activity with a drone.

291
00:16:18,833 --> 00:16:21,466
(eruption echoes)

292
00:16:28,600 --> 00:16:31,600
KULA:
We came here on

293
00:16:31,600 --> 00:16:34,366
the evening of the 14th
of January.

294
00:16:37,000 --> 00:16:41,700
I saw a column of ash and gas...

295
00:16:43,333 --> 00:16:47,233
...almost two miles wide

296
00:16:47,233 --> 00:16:50,833
just rising into the heavens.

297
00:16:50,833 --> 00:16:54,266
(thunder rumbling)

298
00:16:54,266 --> 00:16:56,733
There were
lightning bolts everywhere.

299
00:16:56,733 --> 00:16:59,500
It happened
all around the island.

300
00:16:59,500 --> 00:17:03,366
(thunder rumbling)

301
00:17:03,366 --> 00:17:07,100
It's like shooting several
thousands of crack, firecrackers

302
00:17:07,100 --> 00:17:08,533
all at the same time.

303
00:17:08,533 --> 00:17:11,066
(eruption exploding)

304
00:17:11,066 --> 00:17:15,200
It felt like I'm
witnessing Mother Earth's might

305
00:17:15,200 --> 00:17:18,366
and power being released.

306
00:17:23,666 --> 00:17:27,466
(thunder crashing)

307
00:17:27,466 --> 00:17:32,466
NARRATOR:
Eight hours later,
the volcano stopped erupting.

308
00:17:34,766 --> 00:17:38,833
Then, at 5:15 p.m.
on January 15...

309
00:17:40,600 --> 00:17:44,600
...it produced an eruption over
70 times larger...

310
00:17:46,933 --> 00:17:53,400
...exploding with the power of
over 60 million tons of TNT

311
00:17:53,400 --> 00:17:57,633
and triggering
a series of tsunami waves

312
00:17:57,633 --> 00:18:01,133
that hit Tonga, Australia,

313
00:18:01,133 --> 00:18:05,200
Japan, and the Americas.

314
00:18:05,200 --> 00:18:07,666
Why had this volcano suddenly
produced

315
00:18:07,666 --> 00:18:10,366
such an immense explosion?

316
00:18:11,366 --> 00:18:13,200
Why was it so much more powerful

317
00:18:13,200 --> 00:18:15,866
than the previous day's
eruption?

318
00:18:17,200 --> 00:18:19,400
And is the volcano active enough

319
00:18:19,400 --> 00:18:22,766
to erupt again in the near
future?

320
00:18:26,633 --> 00:18:31,733
First, the team needs to know
the volcano's current activity.

321
00:18:31,733 --> 00:18:34,700
CRONIN (chuckling):
The weather's not ideal.

322
00:18:34,700 --> 00:18:36,633
I mean, the big problem
for us is,

323
00:18:36,633 --> 00:18:38,100
is the sea condition,

324
00:18:38,100 --> 00:18:40,700
and a strong wind is on its way.

325
00:18:40,700 --> 00:18:42,300
So we're really hoping

326
00:18:42,300 --> 00:18:44,100
that we can get all the survey
done

327
00:18:44,100 --> 00:18:47,766
before that, that starts coming
on.

328
00:18:47,766 --> 00:18:50,900
(radio running)

329
00:18:50,900 --> 00:18:54,633
NARRATOR:
Marta is trying to gauge the
volcano's activity using sonar.

330
00:18:54,633 --> 00:18:58,066
(pinging faintly)

331
00:18:58,066 --> 00:19:00,466
The echo sounder
is sending a ping down,

332
00:19:00,466 --> 00:19:03,433
and the reflection of
that ping noise,

333
00:19:03,433 --> 00:19:06,366
 
it's coming back and
it's building up this 3D model

334
00:19:06,366 --> 00:19:09,900
of the sea floor.

335
00:19:09,900 --> 00:19:12,466
NARRATOR:
The scanning will reveal
if magma is dangerously close

336
00:19:12,466 --> 00:19:14,766
to the surface.

337
00:19:14,766 --> 00:19:16,800
♪ ♪

338
00:19:16,800 --> 00:19:20,633
(people talking and laughing
in background)

339
00:19:20,633 --> 00:19:23,633
Wow, these are, it's stronger
than the one before.

340
00:19:23,633 --> 00:19:26,000
CRONIN:
So these are
the shallow ones...

341
00:19:26,000 --> 00:19:28,900
NARRATOR:
Escaping from the sea floor
are plumes of volcanic gases

342
00:19:28,900 --> 00:19:31,200
released by the magma.

343
00:19:31,200 --> 00:19:32,633
1,340 meters.

344
00:19:32,633 --> 00:19:35,033
NARRATOR:
The closer the magma
is to the surface,

345
00:19:35,033 --> 00:19:37,766
the hotter the plumes

346
00:19:37,766 --> 00:19:41,266
and the more likely an eruption.

347
00:19:41,266 --> 00:19:42,833
(talking in background)

348
00:19:45,933 --> 00:19:48,266
CRONIN:
This is a sensor,
which actually measures,

349
00:19:48,266 --> 00:19:51,800
2,000 times a second,
the temperature of the water.

350
00:19:51,800 --> 00:19:54,966
Is the volcano
heating the water, for example?

351
00:19:54,966 --> 00:19:57,333
Is the volcano changing
the water temperature?

352
00:19:57,333 --> 00:20:00,800
It's all the question of whether
the volcano is alive or not.

353
00:20:00,800 --> 00:20:02,633
That's it, that's it, that's it!

354
00:20:02,633 --> 00:20:05,233
RIBÓ:
Careful.

355
00:20:05,233 --> 00:20:06,566
CRONIN:
Down, down, down, quick.

356
00:20:07,900 --> 00:20:10,500
Keep going, yup.

357
00:20:10,500 --> 00:20:12,866
NARRATOR:
Measuring multiple plumes will
reveal how close

358
00:20:12,866 --> 00:20:14,066
the volcano is to erupting.

359
00:20:14,066 --> 00:20:15,233
Running away!

360
00:20:15,233 --> 00:20:17,933
 
(waves crashing, man exclaims)

361
00:20:17,933 --> 00:20:20,633
KULA:
It's a big one!

362
00:20:23,266 --> 00:20:26,933
NARRATOR:
They see a consistent trend.

363
00:20:26,933 --> 00:20:30,033
RIBÓ:
All of the plumes,
they're very weak.

364
00:20:30,033 --> 00:20:33,600
NARRATOR:
The plumes aren't hot.

365
00:20:33,600 --> 00:20:34,933
RIBÓ:
It's still active,

366
00:20:34,933 --> 00:20:38,566
but the strength of the volcano
has decreased.

367
00:20:38,566 --> 00:20:41,466
So for the people of Tonga,
there is still some risk,

368
00:20:41,466 --> 00:20:44,466
but it's less dangerous.

369
00:20:44,466 --> 00:20:48,800
NARRATOR:
The team's findings
suggest the Hunga volcano

370
00:20:48,800 --> 00:20:51,466
won't produce another massive
eruption--

371
00:20:51,466 --> 00:20:53,733
for the time being.

372
00:20:55,466 --> 00:20:57,100
But the events of January 15

373
00:20:57,100 --> 00:21:01,233
show this is
an unpredictable volcano.

374
00:21:03,366 --> 00:21:05,566
Why did it suddenly
produce an eruption

375
00:21:05,566 --> 00:21:08,733
70 times bigger
than the previous day?

376
00:21:12,500 --> 00:21:17,133
It's a question
with global implications.

377
00:21:17,133 --> 00:21:21,166
There could be as many
as 50,000 submarine volcanoes

378
00:21:21,166 --> 00:21:24,266
lurking under
our planet's waves.

379
00:21:24,266 --> 00:21:26,966
In recent years, Kolumbo,

380
00:21:26,966 --> 00:21:29,133
near the Greek island of
Santorini,

381
00:21:29,133 --> 00:21:34,000
and Oomurodashi, less than 40
miles from the center of Tokyo,

382
00:21:34,000 --> 00:21:37,333
have been identified
as active threats.

383
00:21:40,866 --> 00:21:43,633
Knowing exactly how the Hunga
volcano generated

384
00:21:43,633 --> 00:21:45,633
such a powerful eruption

385
00:21:45,633 --> 00:21:47,333
could change our understanding

386
00:21:47,333 --> 00:21:50,100
of the dangers from
submarine volcanoes.

387
00:21:50,100 --> 00:21:52,800
(debris falling,
people shouting)

388
00:21:52,800 --> 00:21:54,133
And the clues

389
00:21:54,133 --> 00:21:56,600
could lie in the ash
Hunga Tonga-Hunga Ha'apai

390
00:21:56,600 --> 00:22:00,400
rained down on the islands.

391
00:22:00,400 --> 00:22:04,333
♪ ♪

392
00:22:04,333 --> 00:22:08,966
The debris contains
time capsules from the eruption,

393
00:22:08,966 --> 00:22:12,066
which volcanologist
Joali Paredes-Mariño analyzes.

394
00:22:14,766 --> 00:22:19,133
The first thing that highlights,
to, to me, is this very dark

395
00:22:19,133 --> 00:22:23,033
and, like, glossy,

396
00:22:23,033 --> 00:22:25,900
blocky particles--
so, that's glass.

397
00:22:27,433 --> 00:22:30,333
NARRATOR:
Volcanic glass
is solidified magma,

398
00:22:30,333 --> 00:22:35,733
created at the very moment
the volcano exploded.

399
00:22:40,366 --> 00:22:42,400
A powerful electron microscope

400
00:22:42,400 --> 00:22:46,666
allows Joali to compare
different samples of glass.

401
00:22:48,533 --> 00:22:51,000
This one's
from a different eruption.

402
00:22:51,000 --> 00:22:53,233
We got this kind of, like,
massive glass,

403
00:22:53,233 --> 00:22:56,600
covered with bubbles.
MAN:
Right.

404
00:22:56,600 --> 00:23:01,600
NARRATOR:
Explosions happen when a
material expands very rapidly.

405
00:23:01,600 --> 00:23:04,333
In most eruptions, this material

406
00:23:04,333 --> 00:23:08,133
is gas in the magma.

407
00:23:09,200 --> 00:23:13,033
Normally, this gas is dissolved
in the liquid magma,

408
00:23:13,033 --> 00:23:16,566
just like in a soda.

409
00:23:16,566 --> 00:23:20,833
If some reason, the pressure
that is on that magma change,

410
00:23:20,833 --> 00:23:23,966
like when you open
a bottle of soda,

411
00:23:23,966 --> 00:23:26,266
you will have all these bubbles.

412
00:23:26,266 --> 00:23:29,666
They will create this inner
force that, at the moment

413
00:23:29,666 --> 00:23:31,166
that it cannot
hold it any longer,

414
00:23:31,166 --> 00:23:32,600
it will fragment the magma.

415
00:23:32,600 --> 00:23:35,766
And that's what creates
an eruption from within.

416
00:23:37,400 --> 00:23:39,800
NARRATOR:
The growing bubbles of gas
inside the magma

417
00:23:39,800 --> 00:23:43,966
cause it to expand rapidly
and explode,

418
00:23:43,966 --> 00:23:48,400
and are clearly visible in
glass from a typical eruption.

419
00:23:50,100 --> 00:23:52,366
But the team sees
something very different

420
00:23:52,366 --> 00:23:56,833
in this sample
from the Hunga volcano.

421
00:23:56,833 --> 00:23:59,833
If we see the one in the center,
you don't see those bubbles.

422
00:23:59,833 --> 00:24:04,233
They have kind of blocky
particles.

423
00:24:04,233 --> 00:24:07,533
NARRATOR:
No bubbles means the
eruption wasn't generated

424
00:24:07,533 --> 00:24:12,266
by the sudden expansion of gas
in the magma.

425
00:24:12,266 --> 00:24:14,900
The shapes of the fragments
point to the explosion

426
00:24:14,900 --> 00:24:19,566
of a completely different
material.

427
00:24:19,566 --> 00:24:22,500
You have this
kind of, like, step fractures.

428
00:24:22,500 --> 00:24:24,900
And also, you can see

429
00:24:24,900 --> 00:24:27,366
the big particle
in the bottom corner.

430
00:24:27,366 --> 00:24:30,133
This is concave fractures.

431
00:24:30,133 --> 00:24:32,533
NARRATOR:
This pattern
of fractures is consistent

432
00:24:32,533 --> 00:24:36,200
with a very
specific explosive event.

433
00:24:36,200 --> 00:24:39,200
That means that is telling
us this is interaction

434
00:24:39,200 --> 00:24:42,066
with magma and water.

435
00:24:42,066 --> 00:24:45,433
NARRATOR:
Water can be extremely
explosive.

436
00:24:45,433 --> 00:24:49,133
If it hits
something as hot as magma,

437
00:24:49,133 --> 00:24:53,266
water instantly turns to gas,

438
00:24:53,266 --> 00:24:56,133
expanding as much as 4,000
times.

439
00:24:56,133 --> 00:24:57,733
(thunder crashing)

440
00:24:57,733 --> 00:24:59,900
It would seem
the most intense eruption

441
00:24:59,900 --> 00:25:01,800
ever witnessed by science

442
00:25:01,800 --> 00:25:05,600
was detonated by the explosion
of water.

443
00:25:08,500 --> 00:25:11,133
♪ ♪

444
00:25:11,133 --> 00:25:14,633
But there is a mystery.

445
00:25:14,633 --> 00:25:19,100
The volcano's magma is usually
locked away from the ocean,

446
00:25:19,100 --> 00:25:23,733
in a chamber over
three miles below the surface.

447
00:25:23,733 --> 00:25:27,066
Why did water and
magma suddenly come into contact

448
00:25:27,066 --> 00:25:30,233
on January 15?

449
00:25:30,233 --> 00:25:32,833
In the global seismic records,

450
00:25:32,833 --> 00:25:37,633
the team spots signals
the satellites didn't detect.

451
00:25:37,633 --> 00:25:39,233
Okay.
That's it?

452
00:25:39,233 --> 00:25:41,766
Uh-huh!
Yes.

453
00:25:41,766 --> 00:25:44,233
NARRATOR:
28 minutes before the big
eruption,

454
00:25:44,233 --> 00:25:49,700
there was a series of smaller,
precursory eruptions.

455
00:25:49,700 --> 00:25:52,433
CRONIN:
We think the precursory
eruptions

456
00:25:52,433 --> 00:25:56,033
led to the rapid fracturing
of the upper volcano.

457
00:25:56,033 --> 00:25:59,633
 
And then seawater gets down
into the magma, and away we go,

458
00:25:59,633 --> 00:26:04,033
and we start a very,
very violent explosion.

459
00:26:05,833 --> 00:26:07,400
NARRATOR:
The magma and water

460
00:26:07,400 --> 00:26:12,233
were separated by thousands
of feet of solid rock.

461
00:26:12,233 --> 00:26:15,533
The team thinks,
on January 15,

462
00:26:15,533 --> 00:26:20,166
the first of the precursory
eruptions cracked open faults.

463
00:26:23,833 --> 00:26:26,500
As this series of eruptions
continued,

464
00:26:26,500 --> 00:26:29,566
these cracks grew bigger.

465
00:26:29,566 --> 00:26:32,433
And bigger.

466
00:26:32,433 --> 00:26:36,933
Until finally, they allowed
cold seawater to flood in,

467
00:26:36,933 --> 00:26:40,500
hitting incredibly hot magma
in the chamber

468
00:26:40,500 --> 00:26:43,400
and generating
the immense explosion.

469
00:26:43,400 --> 00:26:46,200
(booming)

470
00:26:48,866 --> 00:26:52,900
The investigators have made
a major breakthrough:

471
00:26:52,900 --> 00:26:55,433
an explanation for
how the Hunga volcano

472
00:26:55,433 --> 00:27:00,033
could have produced
such a powerful explosion.

473
00:27:00,033 --> 00:27:04,000
But they
face another problem.

474
00:27:04,000 --> 00:27:06,333
(eruption explodes,
thunder crashes)

475
00:27:06,333 --> 00:27:09,766
Most tsunamis are
caused by earthquakes.

476
00:27:09,766 --> 00:27:13,000
Volcanic tsunamis are so rare,

477
00:27:13,000 --> 00:27:15,500
scientists don't know
how the Hunga volcano

478
00:27:15,500 --> 00:27:20,500
generated a series
of enormous waves.

479
00:27:20,500 --> 00:27:24,433
Discovering what happened here
could give new insights

480
00:27:24,433 --> 00:27:29,966
into the global threat
from submarine volcanoes.

481
00:27:29,966 --> 00:27:35,566
The answers could lie
on Tonga's Hihifo peninsula.

482
00:27:38,633 --> 00:27:42,766
Once, this area was dotted
with thriving resorts.

483
00:27:44,833 --> 00:27:49,500
One of the busiest
was owned by Moana Paea.

484
00:27:49,500 --> 00:27:51,666
PAEA:
The whole place

485
00:27:51,666 --> 00:27:55,433
was just full of beautiful
big trees

486
00:27:55,433 --> 00:27:57,833
and coconut trees
and palm trees.

487
00:27:57,833 --> 00:28:00,900
 
You wouldn't
have seen the ocean.

488
00:28:00,900 --> 00:28:04,200
That used to be the tree
with all surfboards on it.

489
00:28:04,200 --> 00:28:08,400
It was a massive tree.

490
00:28:08,400 --> 00:28:10,733
As a kid,
we would climb around it.

491
00:28:10,733 --> 00:28:13,533
But after that tree,
there was a house there,

492
00:28:13,533 --> 00:28:18,733
and then from there
would be the beach area.

493
00:28:20,166 --> 00:28:22,533
NARRATOR:
The Hihifo peninsula lies

494
00:28:22,533 --> 00:28:27,066
on the northwest coast of
Tongatapu.

495
00:28:27,066 --> 00:28:29,466
Less than 40 miles due north

496
00:28:29,466 --> 00:28:33,333
is the volcano
Hunga Tonga-Hunga Ha'apai.

497
00:28:33,333 --> 00:28:36,566
(volcano rumbling,
thunder crashing)

498
00:28:36,566 --> 00:28:41,300
PAEA:
The volcano was going crazy,
striking lightning and stuff.

499
00:28:41,300 --> 00:28:43,866
Because it'd been happening
for weeks and weeks,

500
00:28:43,866 --> 00:28:46,666
we kind of took it for granted
that it must be all right.

501
00:28:46,666 --> 00:28:48,900
♪ ♪

502
00:28:48,900 --> 00:28:50,500
We had a full hotel,

503
00:28:50,500 --> 00:28:53,900
and maybe quarter past five,
I heard screaming.

504
00:28:53,900 --> 00:28:55,400
MAN:
Here!

505
00:28:55,400 --> 00:28:56,800
PAEA:
One of my staff said,

506
00:28:56,800 --> 00:28:58,866
"Hey, look at the water."

507
00:28:58,866 --> 00:29:00,866
It looked like
a washing machine.

508
00:29:00,866 --> 00:29:02,433
(man exclaims)

509
00:29:02,433 --> 00:29:05,366
And I just screamed,
"It's a tsunami!"

510
00:29:05,366 --> 00:29:07,466
(people yelling in background)

511
00:29:07,466 --> 00:29:09,400
PAEA:
And people were going to
pack their clothes,

512
00:29:09,400 --> 00:29:11,366
and I said,
"No, you need to get out!"

513
00:29:11,366 --> 00:29:13,766
One family literally
just got out of the pool

514
00:29:13,766 --> 00:29:15,233
and got in their car
and took off.

515
00:29:15,233 --> 00:29:17,266
(men speaking indistinctly)

516
00:29:17,266 --> 00:29:18,533
PAEA:
That's when I saw...

517
00:29:18,533 --> 00:29:20,166
MAN:
Oh, my God.

518
00:29:20,166 --> 00:29:24,000
PAEA:
...the water is moving fast,
but growing.

519
00:29:24,000 --> 00:29:25,566
So we ran through here.

520
00:29:25,566 --> 00:29:29,366
(people exclaiming)
WOMAN: Oh! Oh, (bleep)!

521
00:29:29,366 --> 00:29:31,266
PAEA:
We were yelling,
"Tsunami! Tsunami!"

522
00:29:31,266 --> 00:29:32,600
MAN:
Holy (bleep)!

523
00:29:32,600 --> 00:29:34,533
(people exclaiming)

524
00:29:34,533 --> 00:29:35,600
PAEA:
And my son was, like,

525
00:29:35,600 --> 00:29:37,433
"Mom, let's climb a tree."

526
00:29:37,433 --> 00:29:38,900
And then, suddenly...

527
00:29:38,900 --> 00:29:40,066
(explosion pounds)

528
00:29:40,066 --> 00:29:41,200
MAN:
Oh, (bleep)!

529
00:29:41,200 --> 00:29:42,200
WOMAN:
Whoa!

530
00:29:42,200 --> 00:29:43,700
MAN:
Holy (bleep)!

531
00:29:43,700 --> 00:29:46,133
PAEA:
Another massive explosion.

532
00:29:46,133 --> 00:29:47,166
MAN:
Tsunami's heading in.

533
00:29:47,166 --> 00:29:48,933
(people exclaiming)
(bleep)

534
00:29:48,933 --> 00:29:51,200
The pressure of it
threw all of us on the ground.

535
00:29:51,200 --> 00:29:53,566
My daughter
was crying, "My ears!"

536
00:29:53,566 --> 00:29:56,133
But my sons are, like,
"Mom, get up, get up!"

537
00:29:56,133 --> 00:30:00,033
Because we could still hear
waves rumbling.

538
00:30:00,033 --> 00:30:02,766
(men shouting indistinctly)

539
00:30:02,766 --> 00:30:03,966
MAN:
Okay, okay!

540
00:30:03,966 --> 00:30:06,266
(baby crying)

541
00:30:06,266 --> 00:30:07,833
(man panting)

542
00:30:07,833 --> 00:30:09,566
MAN:
Here!

543
00:30:09,566 --> 00:30:12,066
(waves crashing, water rushing)

544
00:30:12,066 --> 00:30:13,833
PAEA:
And when we got down
to the road,

545
00:30:13,833 --> 00:30:16,300
there's this
two-story house there,

546
00:30:16,300 --> 00:30:18,633
and there were all
these village people

547
00:30:18,633 --> 00:30:20,600
up on top of there,
and it started to

548
00:30:20,600 --> 00:30:22,333
rain down with dust.

549
00:30:22,333 --> 00:30:25,100
(baby crying,
people murmuring and exclaiming)

550
00:30:25,100 --> 00:30:26,733
(water rushing)

551
00:30:26,733 --> 00:30:29,300
PAEA:
When we got to the roof,

552
00:30:29,300 --> 00:30:34,166
we saw the big swell
coming across.

553
00:30:34,166 --> 00:30:37,300
(people whimpering and shouting)

554
00:30:37,300 --> 00:30:38,566
PAEA:
We were praying and singing.

555
00:30:38,566 --> 00:30:42,266
And then my brother came,
so we all came down.

556
00:30:42,266 --> 00:30:43,566
(water rushing)

557
00:30:43,566 --> 00:30:45,966
We got in the car,
and it being so dark,

558
00:30:45,966 --> 00:30:49,400
and the dust was massive,
and rocks coming...

559
00:30:49,400 --> 00:30:50,966
(debris pelting)
CHILD:
Mommy...

560
00:30:50,966 --> 00:30:54,833
PAEA: And they weren't
just little rocks.
(debris pelting)

561
00:30:54,833 --> 00:30:57,866
(people whimpering, murmuring)

562
00:30:57,866 --> 00:31:01,266
♪ ♪

563
00:31:01,266 --> 00:31:04,133
(people speaking in background)

564
00:31:04,133 --> 00:31:05,500
NARRATOR:
Like many Tongans,

565
00:31:05,500 --> 00:31:07,933
Moana headed for
the safety of high ground.

566
00:31:10,133 --> 00:31:13,333
♪ ♪

567
00:31:13,333 --> 00:31:17,333
The next day revealed
the scale of the destruction.

568
00:31:17,333 --> 00:31:22,366
♪ ♪

569
00:31:26,366 --> 00:31:30,366
PAEA:
I remember one of my staff
ringing up the next morning.

570
00:31:31,966 --> 00:31:34,700
(voice breaking):
And he's saying, "Sorry, Moana,

571
00:31:34,700 --> 00:31:37,266
everything is gone."

572
00:31:37,266 --> 00:31:39,233
And I said to him,
"Praise God,

573
00:31:39,233 --> 00:31:41,233
"we are all still alive.

574
00:31:41,233 --> 00:31:43,333
That's the main thing."
(sniffs)

575
00:31:43,333 --> 00:31:46,833
(breath trembles)

576
00:31:46,833 --> 00:31:52,133
♪ ♪

577
00:31:52,133 --> 00:31:54,100
We loved it here.

578
00:31:54,100 --> 00:31:56,066
Such a beautiful space.

579
00:31:56,066 --> 00:31:58,100
(gasps)

580
00:31:58,100 --> 00:32:00,933
It was very hard to see,

581
00:32:00,933 --> 00:32:03,833
because this is our livelihood,

582
00:32:03,833 --> 00:32:06,633
and this is something
that has looked after...

583
00:32:06,633 --> 00:32:08,633
(sniffles):
...our community for many years.

584
00:32:08,633 --> 00:32:12,566
(sniffles, breathes deeply)

585
00:32:12,566 --> 00:32:14,333
♪ ♪

586
00:32:14,333 --> 00:32:19,700
NARRATOR:
Ahead of Moana lies months
of rebuilding.

587
00:32:19,700 --> 00:32:26,833
This is the stark reality
of the tsunami that hit Tonga.

588
00:32:26,833 --> 00:32:29,933
But this event
is also a mystery.

589
00:32:29,933 --> 00:32:35,266
How did the volcano generate
such destructive waves?

590
00:32:39,600 --> 00:32:43,533
Tsunami scientist Jose Borrero
has flown in to investigate.

591
00:32:43,533 --> 00:32:45,533
(wind blowing)

592
00:32:45,533 --> 00:32:47,066
(shutter clicking)

593
00:32:47,066 --> 00:32:50,133
BORRERO:
As tsunami waves
propagate through the ocean,

594
00:32:50,133 --> 00:32:53,400
their speed is governed
by the depth of the water.

595
00:32:53,400 --> 00:32:55,966
So, the deeper the water,
the faster they can go.

596
00:32:55,966 --> 00:32:59,166
Now, where we are,
on the west coast of Tongatapu,

597
00:32:59,166 --> 00:33:01,100
there was a very narrow
fringing reef,

598
00:33:01,100 --> 00:33:02,300
and you can see the reef here.

599
00:33:02,300 --> 00:33:05,166
It was where
the waves are breaking.

600
00:33:05,166 --> 00:33:07,966
 
Just on the other side
of that reef,

601
00:33:07,966 --> 00:33:11,233
the water drops off to
about a depth of

602
00:33:11,233 --> 00:33:14,433
just over 1,000 meters.

603
00:33:14,433 --> 00:33:18,600
It's deep water from here
out to the Hunga volcano.

604
00:33:18,600 --> 00:33:22,133
♪ ♪

605
00:33:22,133 --> 00:33:24,800
The tsunami came
directly in here, unimpeded.

606
00:33:24,800 --> 00:33:27,200
There was no reefs
or features

607
00:33:27,200 --> 00:33:30,033
or anything in the way
to slow it down, redirect it.

608
00:33:30,033 --> 00:33:31,933
♪ ♪

609
00:33:31,933 --> 00:33:34,966
And the tsunami
takes only eight minutes

610
00:33:34,966 --> 00:33:37,733
to get from the volcano
to here.

611
00:33:37,733 --> 00:33:40,066
♪ ♪

612
00:33:40,066 --> 00:33:43,933
NARRATOR:
A wave with immense power
arrived at the peninsula

613
00:33:43,933 --> 00:33:47,000
and caused widespread damage

614
00:33:47,000 --> 00:33:50,666
because of what happens when
a tsunami enters shallow water.

615
00:33:50,666 --> 00:33:53,400
♪ ♪

616
00:33:55,066 --> 00:33:57,900
The energy of a tsunami
is spread throughout

617
00:33:57,900 --> 00:34:00,333
the depth of the ocean.

618
00:34:00,333 --> 00:34:01,866
In deep water,

619
00:34:01,866 --> 00:34:06,566
this makes the height
of the wave barely noticeable.

620
00:34:06,566 --> 00:34:08,966
But as the wave reaches
shallow water,

621
00:34:08,966 --> 00:34:12,533
it is slowed dramatically,

622
00:34:12,533 --> 00:34:16,266
and the water begins
to pile up,

623
00:34:16,266 --> 00:34:21,166
making the wave
higher and higher.

624
00:34:21,166 --> 00:34:25,166
BORRERO:
When a tsunami comes ashore,

625
00:34:25,166 --> 00:34:27,600
it's not just the water
that causes the damage.

626
00:34:27,600 --> 00:34:30,100
It starts to pick things up.

627
00:34:30,100 --> 00:34:32,433
It starts with boulders
and sand.

628
00:34:32,433 --> 00:34:35,433
And then it knocks down trees,

629
00:34:35,433 --> 00:34:37,533
and the trees become
entrained in the flow.

630
00:34:37,533 --> 00:34:39,466
Then it'll take out a house,

631
00:34:39,466 --> 00:34:43,033
and the material from the house
will become part of the flow.

632
00:34:43,033 --> 00:34:45,966
And all of this material
gradually builds up

633
00:34:45,966 --> 00:34:47,633
until it's, it's not even water
anymore.

634
00:34:47,633 --> 00:34:51,833
It's a dense debris flow

635
00:34:51,833 --> 00:34:55,400
of everything that the wave
has picked up along the way.

636
00:34:55,400 --> 00:35:01,366
♪ ♪

637
00:35:02,933 --> 00:35:06,000
NARRATOR:
Jose's first task is working out
the height and power

638
00:35:06,000 --> 00:35:09,033
of the incoming wave.

639
00:35:09,033 --> 00:35:12,766
And the trail of destruction
offers him the vital clues.

640
00:35:12,766 --> 00:35:13,966
This is weird.

641
00:35:15,700 --> 00:35:17,200
 
This stuff is

642
00:35:17,200 --> 00:35:19,766
very difficult
to bend with your hand,

643
00:35:19,766 --> 00:35:21,033
but the way we see it here,

644
00:35:21,033 --> 00:35:22,966
just wrapped around
a concrete pillar

645
00:35:22,966 --> 00:35:27,533
like tissue paper,
but with roofing steel.

646
00:35:27,533 --> 00:35:32,433
NARRATOR:
First, Jose needs to find
the wave's direction.

647
00:35:32,433 --> 00:35:34,766
Over here,

648
00:35:34,766 --> 00:35:38,233
we see these
concrete columns

649
00:35:38,233 --> 00:35:42,900
are knocked down in the
direction the wave was going.

650
00:35:42,900 --> 00:35:44,866
So the wave came from
behind us,

651
00:35:44,866 --> 00:35:47,500
from the north,
swept down the beach,

652
00:35:47,500 --> 00:35:50,700
and took out these columns,
laying them down that way.

653
00:35:52,300 --> 00:35:54,966
NARRATOR:
Following the trail of debris
inland,

654
00:35:54,966 --> 00:35:58,933
Jose can find
the evidence he needs.

655
00:35:58,933 --> 00:36:00,666
♪ ♪

656
00:36:00,666 --> 00:36:03,933
BORRERO:
Up here is one of the most
crucial bits of information

657
00:36:03,933 --> 00:36:06,200
from the whole tsunami event.

658
00:36:06,200 --> 00:36:09,233
This was a cell phone tower.

659
00:36:09,233 --> 00:36:11,766
And on the cell phone tower
was a weather station,

660
00:36:11,766 --> 00:36:14,500
and, as you can see,
was completely obliterated

661
00:36:14,500 --> 00:36:17,700
by the tsunami surge.

662
00:36:17,700 --> 00:36:20,433
This is a very
strong piece of equipment.

663
00:36:20,433 --> 00:36:23,133
It's a big, strong thing.

664
00:36:23,133 --> 00:36:25,233
This was
a 20-meter-tall tower.

665
00:36:25,233 --> 00:36:29,900
But yet the force was able
to bend the entire thing over.

666
00:36:32,066 --> 00:36:34,866
And 200 meters inland,
on one of the trees

667
00:36:34,866 --> 00:36:38,400
is pieces of this tower
still hanging from a branch

668
00:36:38,400 --> 00:36:42,200
five to six meters
above the ground.

669
00:36:42,200 --> 00:36:45,566
NARRATOR:
Bringing all of this
information together,

670
00:36:45,566 --> 00:36:48,166
Jose can compute
the scale of the tsunami.

671
00:36:48,166 --> 00:36:50,466
♪ ♪

672
00:36:50,466 --> 00:36:52,966
BORRERO:
So the ground level
that we're standing at

673
00:36:52,966 --> 00:36:55,000
is about 13 meters
above sea level.

674
00:36:55,000 --> 00:36:57,400
And then with the flow marks
around this area,

675
00:36:57,400 --> 00:37:00,466
we know that the tsunami
flow depth through here was

676
00:37:00,466 --> 00:37:02,233
somewhere to
five to six meters.

677
00:37:02,233 --> 00:37:05,633
So we're talking,
you know, 18, 19 meters

678
00:37:05,633 --> 00:37:08,900
of, of total tsunami height
passing through this area.

679
00:37:11,700 --> 00:37:16,833
NARRATOR:
19 meters is over 60 feet--

680
00:37:16,833 --> 00:37:20,900
about the height
of a six-story building.

681
00:37:22,700 --> 00:37:25,133
(water rushing)

682
00:37:25,133 --> 00:37:29,500
NARRATOR:
In 2011, a massive earthquake
unleashed a tsunami on Japan.

683
00:37:29,500 --> 00:37:31,833
(people screaming)

684
00:37:31,833 --> 00:37:33,666
NARRATOR:
Despite being protected by
a breakwater

685
00:37:33,666 --> 00:37:37,000
costing some $1.6 billion,

686
00:37:37,000 --> 00:37:39,400
Kamaishi City
was hit by a wave

687
00:37:39,400 --> 00:37:42,900
that measured 26 feet tall.

688
00:37:42,900 --> 00:37:45,466
(water rushing)

689
00:37:45,466 --> 00:37:49,400
All of this damage
was caused by a wave

690
00:37:49,400 --> 00:37:54,066
less than half the height
of the Hihifo tsunami.

691
00:37:54,066 --> 00:37:57,733
♪ ♪

692
00:37:57,733 --> 00:38:01,966
How did the Hunga volcano
generate such an immense wave?

693
00:38:01,966 --> 00:38:05,400
(men exclaiming)

694
00:38:05,400 --> 00:38:06,600
BORRERO:
So, yeah, this is you guys

695
00:38:06,600 --> 00:38:08,300
parked up here.
Yes.

696
00:38:08,300 --> 00:38:09,666
NARRATOR:
To find out,

697
00:38:09,666 --> 00:38:14,166
Jose gathers eyewitness
testimony and video.

698
00:38:14,166 --> 00:38:16,633
MAN 2:
I was the driver of that car.

699
00:38:16,633 --> 00:38:19,133
BORRERO: Were you waiting for
someone to come?
No.

700
00:38:19,133 --> 00:38:20,533
We were waiting
because the...

701
00:38:20,533 --> 00:38:22,733
The road! Over the road.
The road was busy.

702
00:38:22,733 --> 00:38:27,100
(laughs):
And the waves
began banging on the car.

703
00:38:27,100 --> 00:38:30,933
(all exclaiming in video)

704
00:38:30,933 --> 00:38:32,533
(video rewinding)

705
00:38:32,533 --> 00:38:35,133
NARRATOR:
Jose is combining
this firsthand evidence

706
00:38:35,133 --> 00:38:39,033
with images and videos
he has found on social media.

707
00:38:41,133 --> 00:38:42,400
BORRERO:
It's astounding,

708
00:38:42,400 --> 00:38:44,266
the amount of material
that's available online.

709
00:38:44,266 --> 00:38:45,766
People just post things up,

710
00:38:45,766 --> 00:38:48,333
and all of this
is completely useful

711
00:38:48,333 --> 00:38:49,333
in a scientific sense.

712
00:38:49,333 --> 00:38:51,566
We have a set of videos

713
00:38:51,566 --> 00:38:53,333
that show a series
of tsunami waves,

714
00:38:53,333 --> 00:38:56,566
and we know what time
the video was taken.

715
00:38:56,566 --> 00:38:59,000
And by knowing the timing
of when it's hitting the coast,

716
00:38:59,000 --> 00:39:00,366
it gives us clues as to

717
00:39:00,366 --> 00:39:04,300
how that wave was generated
at the volcano.

718
00:39:04,300 --> 00:39:06,800
NARRATOR:
Jose has built
a timeline of the day.

719
00:39:06,800 --> 00:39:08,266
(eruption explodes in distance)
MAN 1: Oh! MAN 2: Whoo!

720
00:39:08,266 --> 00:39:10,033
MAN 1:
Holy (bleep)!

721
00:39:10,033 --> 00:39:14,133
NARRATOR:
He's identified not one,
but two tsunamis--

722
00:39:14,133 --> 00:39:17,966
one at 5:23
and one at 5:34.

723
00:39:17,966 --> 00:39:19,100
(mouse clicking)

724
00:39:19,100 --> 00:39:21,300
Tracking back
eight minutes from each,

725
00:39:21,300 --> 00:39:23,300
he finds the same thing.

726
00:39:24,966 --> 00:39:27,266
An eruption at the volcano.

727
00:39:27,266 --> 00:39:30,266
♪ ♪

728
00:39:30,266 --> 00:39:32,500
This fits with one theory

729
00:39:32,500 --> 00:39:37,066
of how submarine volcanoes
produce tsunamis.

730
00:39:37,066 --> 00:39:41,633
As material erupts upwards,
it pushes water out of the way,

731
00:39:41,633 --> 00:39:45,566
creating immense waves that
radiate out from the volcano.

732
00:39:49,766 --> 00:39:52,966
But Jose doesn't think
these eruptions

733
00:39:52,966 --> 00:39:56,466
can explain the destructive
60-foot-high tsunami.

734
00:39:56,466 --> 00:39:58,400
♪ ♪

735
00:39:58,400 --> 00:39:59,933
BORRERO:
We know the weather station

736
00:39:59,933 --> 00:40:02,866
transmitted its last packet
of data at 6:00 p.m.

737
00:40:02,866 --> 00:40:05,066
So we know a tsunami

738
00:40:05,066 --> 00:40:06,800
could not have destroyed
the weather station

739
00:40:06,800 --> 00:40:08,900
and the cell phone tower
that it was attached to

740
00:40:08,900 --> 00:40:12,100
until sometime after 6:00 p.m.

741
00:40:12,100 --> 00:40:16,800
This means that
there was a later wave.

742
00:40:16,800 --> 00:40:18,666
But this doesn't fit

743
00:40:18,666 --> 00:40:20,733
with the idea that
the wave was generated

744
00:40:20,733 --> 00:40:22,766
during these two
volcanic eruptions.

745
00:40:22,766 --> 00:40:27,233
♪ ♪

746
00:40:27,233 --> 00:40:28,800
NARRATOR:
If it wasn't an eruption,

747
00:40:28,800 --> 00:40:31,566
what other event
at the Hunga volcano

748
00:40:31,566 --> 00:40:33,566
would have enough power
to unleash

749
00:40:33,566 --> 00:40:35,833
a 60-foot-high tsunami?

750
00:40:35,833 --> 00:40:38,733
(eruption thundering)

751
00:40:38,733 --> 00:40:41,233
(roaring)

752
00:40:41,233 --> 00:40:45,666
One possibility lies with
the speed it threw out material.

753
00:40:47,400 --> 00:40:49,866
CRONIN:
During the first
one-and-a-half hours,

754
00:40:49,866 --> 00:40:54,600
it was ejecting material
at a rate twice as much as

755
00:40:54,600 --> 00:40:56,733
the next-biggest eruption
that we know of.

756
00:40:56,733 --> 00:41:01,333
It threw out
seven cubic kilometers of

757
00:41:01,333 --> 00:41:03,400
dense rock material.

758
00:41:03,400 --> 00:41:07,700
NARRATOR:
That's enough to cover
the entire island of Manhattan

759
00:41:07,700 --> 00:41:11,633
in nearly
400 feet of debris.

760
00:41:11,633 --> 00:41:15,200
CRONIN:
When a large amount of magma
erupts from a volcano,

761
00:41:15,200 --> 00:41:17,666
large amounts of magma
come out at once.

762
00:41:17,666 --> 00:41:20,133
And so that means that
the top part of the volcano

763
00:41:20,133 --> 00:41:23,300
actually then
sinks in on itself.

764
00:41:23,300 --> 00:41:26,433
NARRATOR:
Shane's idea is that

765
00:41:26,433 --> 00:41:29,300
as material erupted out
of the magma chamber,

766
00:41:29,300 --> 00:41:34,433
it created a larger and larger
void underground.

767
00:41:34,433 --> 00:41:38,500
When it could no longer support
the weight of material above,

768
00:41:38,500 --> 00:41:43,633
the entire caldera dropped
over 2,300 feet.

769
00:41:43,633 --> 00:41:46,666
Seawater flooded in,

770
00:41:46,666 --> 00:41:48,766
kickstarting tsunamis
that radiated

771
00:41:48,766 --> 00:41:53,000
out from the volcano,

772
00:41:53,000 --> 00:41:55,400
an explanation
of how the volcano

773
00:41:55,400 --> 00:41:59,566
could generate
a 60-foot wave.

774
00:41:59,566 --> 00:42:04,533
♪ ♪

775
00:42:04,533 --> 00:42:06,800
The team has found
that a caldera

776
00:42:06,800 --> 00:42:09,333
where the water can
get into the magma chamber

777
00:42:09,333 --> 00:42:12,333
can erupt explosively

778
00:42:12,333 --> 00:42:14,866
and generate
life-threatening tsunamis,

779
00:42:14,866 --> 00:42:19,166
heightening the need to monitor
these types of volcanoes.

780
00:42:22,300 --> 00:42:26,566
And only 55 miles from
Hunga Tonga-Hunga Ha'apai

781
00:42:26,566 --> 00:42:29,433
is its volcanic twin:

782
00:42:29,433 --> 00:42:32,566
the island of Tofua.

783
00:42:32,566 --> 00:42:34,733
Just like the Hunga volcano,

784
00:42:34,733 --> 00:42:39,500
Tofua has a two-and-a-half-
mile-wide caldera.

785
00:42:41,866 --> 00:42:47,166
But its magma chamber
is far closer to the surface,

786
00:42:47,166 --> 00:42:52,600
and far closer to
the surrounding seawater.

787
00:42:52,600 --> 00:42:55,900
♪ ♪

788
00:42:55,900 --> 00:42:57,166
KULA:
Captain,

789
00:42:57,166 --> 00:43:00,433
we're keeping
a straight line.

790
00:43:00,433 --> 00:43:01,966
We're about here.

791
00:43:01,966 --> 00:43:04,533
CRONIN:
It's a very remote part
of the world,

792
00:43:04,533 --> 00:43:06,033
and so no one's been able
to get here.

793
00:43:06,033 --> 00:43:09,566
It's 14 hours on the boat,

794
00:43:09,566 --> 00:43:11,700
and out here,
the ocean can be

795
00:43:11,700 --> 00:43:14,066
extremely treacherous.

796
00:43:14,066 --> 00:43:17,133
♪ ♪

797
00:43:17,133 --> 00:43:19,200
All previous measurements

798
00:43:19,200 --> 00:43:22,366
have been made
from satellite observations,

799
00:43:22,366 --> 00:43:26,466
so it's critical that we try
to land on the island.

800
00:43:26,466 --> 00:43:28,333
NARRATOR:
The satellites suggest

801
00:43:28,333 --> 00:43:31,166
there is virtually no activity
at Tofua.

802
00:43:31,166 --> 00:43:36,300
But this has never been verified
with field measurements.

803
00:43:40,366 --> 00:43:44,633
NARRATOR:
Taaniela and Shane
enlist the help of boatmen

804
00:43:44,633 --> 00:43:46,833
from the neighboring island
of Kotu.

805
00:43:46,833 --> 00:43:49,133
(motor humming)

806
00:43:49,133 --> 00:43:51,700
They report having seen

807
00:43:51,700 --> 00:43:54,800
a red glow
above Tofua at night.

808
00:43:57,566 --> 00:44:02,066
♪ ♪

809
00:44:05,500 --> 00:44:09,800
KULA:
I feel excited to go up
for the first time.

810
00:44:09,800 --> 00:44:13,500
We hope to get some real data
on the ground.

811
00:44:13,500 --> 00:44:16,800
And then, uh,
we can share it with the world.

812
00:44:16,800 --> 00:44:19,433
♪ ♪

813
00:44:19,433 --> 00:44:21,666
NARRATOR:
First, they need to ascend

814
00:44:21,666 --> 00:44:27,566
over 1,500 feet
through tropical forests.

815
00:44:27,566 --> 00:44:31,766
♪ ♪

816
00:44:31,766 --> 00:44:33,933
CRONIN:
It's quite humid.

817
00:44:33,933 --> 00:44:35,466
So...

818
00:44:35,466 --> 00:44:38,366
I think my sweat is
on top of my sweat,

819
00:44:38,366 --> 00:44:41,466
building up
a third layer of sweat.

820
00:44:41,466 --> 00:44:43,900
(grunts)

821
00:44:43,900 --> 00:44:47,700
♪ ♪

822
00:44:50,000 --> 00:44:52,966
NARRATOR:
Their first objective:

823
00:44:52,966 --> 00:44:56,500
the rim of Tofua's
two-and-a-half-mile-wide crater.

824
00:44:58,200 --> 00:45:03,633
CRONIN:
Look, look, this is
a big caldera.

825
00:45:03,633 --> 00:45:06,700
Yeah,
so there's the active cone.

826
00:45:06,700 --> 00:45:09,466
That's our destination,
should we decide to accept it.

827
00:45:12,033 --> 00:45:14,666
NARRATOR:
Shane suspects the satellites
are wrong

828
00:45:14,666 --> 00:45:17,733
and Tofua could be due an
eruption.

829
00:45:20,233 --> 00:45:23,666
CRONIN:
We had a big eruption around
1,200 years ago,

830
00:45:23,666 --> 00:45:27,366
another big one
around 800 years ago,

831
00:45:27,366 --> 00:45:32,400
and the most recent one
around 400 years ago.

832
00:45:32,400 --> 00:45:36,333
NARRATOR:
This pattern suggests
Tofua should erupt again,

833
00:45:36,333 --> 00:45:38,200
and soon.

834
00:45:40,766 --> 00:45:41,933
(camera shutter clicks)

835
00:45:41,933 --> 00:45:43,233
CRONIN:
Okay, it's fantastic.

836
00:45:43,233 --> 00:45:44,700
We've got a bit of a break
in the weather.

837
00:45:44,700 --> 00:45:47,866
You can see how blue that gas is
coming off that volcano.

838
00:45:50,700 --> 00:45:54,866
When the color of the gas
is blue, it's sulfur dioxide.

839
00:45:54,866 --> 00:45:58,600
NARRATOR:
This gas is released by
the magma.

840
00:46:01,066 --> 00:46:03,066
The blue color
is only visible

841
00:46:03,066 --> 00:46:08,166
if the levels of sulfur dioxide
are high.

842
00:46:08,166 --> 00:46:09,400
CRONIN:
So I think the magma

843
00:46:09,400 --> 00:46:10,933
must be very close to the...
(shutter clicks)

844
00:46:10,933 --> 00:46:13,766
...close to the surface,
actually.

845
00:46:13,766 --> 00:46:16,200
(shutter clicks)

846
00:46:16,200 --> 00:46:18,200
And this corresponds to

847
00:46:18,200 --> 00:46:19,833
what the locals
have been reporting

848
00:46:19,833 --> 00:46:22,300
over the last
couple of months,

849
00:46:22,300 --> 00:46:25,866
is that there is
a glow in the sky above Tofua

850
00:46:25,866 --> 00:46:29,233
when there's a cloudy evening.

851
00:46:32,100 --> 00:46:35,300
NARRATOR:
The signs point to Tofua being
far more active

852
00:46:35,300 --> 00:46:39,366
than the satellite readings
suggest.

853
00:46:40,766 --> 00:46:43,133
But to know the level
of the threat,

854
00:46:43,133 --> 00:46:46,000
the team needs more evidence.

855
00:46:50,200 --> 00:46:55,900
Taaniela will use a drone
to investigate the active cone.

856
00:46:57,366 --> 00:47:00,633
While the rest of the team
will collect vital readings,

857
00:47:00,633 --> 00:47:04,566
which need to be taken
from inside the caldera itself.

858
00:47:05,966 --> 00:47:09,800
♪ ♪

859
00:47:15,833 --> 00:47:21,133
CRONIN:
I'm going to try and get
a position close to the plume.

860
00:47:21,133 --> 00:47:23,333
I don't want to go
underneath it,

861
00:47:23,333 --> 00:47:26,700
because sulfur dioxide is
actually quite lethal.

862
00:47:26,700 --> 00:47:29,866
We can then try to measure
some of the output.

863
00:47:34,000 --> 00:47:36,833
This is what I've been
lugging up the hill.

864
00:47:38,566 --> 00:47:41,500
NARRATOR:
Volcanologists monitor
the sulfur dioxide

865
00:47:41,500 --> 00:47:45,400
to gauge the activity
of volcanoes.

866
00:47:45,400 --> 00:47:48,366
CRONIN:
This is the telescope.

867
00:47:48,366 --> 00:47:49,966
And it's a rotating one.

868
00:47:49,966 --> 00:47:52,266
NARRATOR:
The more sulfur dioxide

869
00:47:52,266 --> 00:47:54,000
Shane detects,
the more active

870
00:47:54,000 --> 00:47:55,633
the volcano.

871
00:47:55,633 --> 00:47:56,833
Now...

872
00:47:58,633 --> 00:48:00,633
It's going to be scanning
over there,

873
00:48:00,633 --> 00:48:02,033
and I want it to scan
above the level

874
00:48:02,033 --> 00:48:04,166
of the
opposite caldera rim.

875
00:48:06,533 --> 00:48:09,366
We're capturing it
beautifully with this angle.

876
00:48:09,366 --> 00:48:15,400
♪ ♪

877
00:48:15,400 --> 00:48:17,633
NARRATOR:
Shane's readings indicate
the satellites have been

878
00:48:17,633 --> 00:48:20,933
dangerously underestimating
the levels of sulfur dioxide.

879
00:48:23,066 --> 00:48:27,100
Tofua is releasing far more
than previously thought.

880
00:48:27,100 --> 00:48:33,100
♪ ♪

881
00:48:33,100 --> 00:48:35,933
Taaniela's expert flying
reveals that

882
00:48:35,933 --> 00:48:39,933
the magma has
welled up in the crater,

883
00:48:39,933 --> 00:48:42,833
creating a lava lake,

884
00:48:42,833 --> 00:48:47,400
one of fewer than ten
on the entire planet.

885
00:48:52,033 --> 00:48:56,200
And there's a sign Tofua has
been actively throwing out lava,

886
00:48:56,200 --> 00:48:58,433
incredibly recently.

887
00:48:58,433 --> 00:49:02,033
CRONIN:
This erupted in the last
few days.

888
00:49:02,033 --> 00:49:03,566
It's a fresh volcanic bomb.

889
00:49:03,566 --> 00:49:05,866
So this really contrasts to

890
00:49:05,866 --> 00:49:07,866
all of the rest of
the older material around here.

891
00:49:07,866 --> 00:49:13,066
So there's been some quite
big explosions to produce these.

892
00:49:13,066 --> 00:49:15,666
It's really interesting,
because it looks as if

893
00:49:15,666 --> 00:49:17,300
Tofua is entering
a new phase of activity,

894
00:49:17,300 --> 00:49:20,300
one that we haven't
seen here before.

895
00:49:20,300 --> 00:49:23,033
♪ ♪

896
00:49:23,033 --> 00:49:24,933
Everything that we've
discovered today

897
00:49:24,933 --> 00:49:27,333
is absolutely new,
and I think will be

898
00:49:27,333 --> 00:49:30,733
quite a shock
around the globe.

899
00:49:32,233 --> 00:49:34,433
NARRATOR:
Tonga is still recovering

900
00:49:34,433 --> 00:49:38,633
from the eruption of
the Hunga volcano.

901
00:49:38,633 --> 00:49:40,966
Now
scientists have discovered

902
00:49:40,966 --> 00:49:43,233
that its volcanic twin,
Tofua,

903
00:49:43,233 --> 00:49:44,800
is far more active

904
00:49:44,800 --> 00:49:48,266
than satellites have
led them to believe,

905
00:49:48,266 --> 00:49:52,900
a finding that has implications
far beyond Tonga.

906
00:49:52,900 --> 00:49:55,166
♪ ♪

907
00:49:58,133 --> 00:50:02,300
KULA:
Our latest expedition
really showed us

908
00:50:02,300 --> 00:50:06,533
there are limitations
of the satellite system.

909
00:50:06,533 --> 00:50:10,566
You always need to be on-site
to actually know

910
00:50:10,566 --> 00:50:15,133
the full level of
the volcanic activity.

911
00:50:16,533 --> 00:50:21,266
NARRATOR:
With as many as 50,000 submarine
volcanoes around the planet,

912
00:50:21,266 --> 00:50:23,400
the world needs
to find better ways of

913
00:50:23,400 --> 00:50:26,933
keeping an eye on these
destructive forces of nature.

914
00:50:26,933 --> 00:50:31,300
♪ ♪

915
00:50:31,300 --> 00:50:34,100
And be ready

916
00:50:34,100 --> 00:50:36,800
for the next
Hunga Tonga-Hunga Ha'apai.

917
00:50:36,800 --> 00:50:40,466
(people exclaiming)

918
00:50:40,466 --> 00:50:42,700
(speaking Tongan):

919
00:50:42,700 --> 00:50:44,966
NARRATOR:
Taaniela and his colleagues

920
00:50:44,966 --> 00:50:47,933
have long reached out to
people of Tonga.

921
00:50:47,933 --> 00:50:51,033
ANA MAEA
(speaking Tongan):

922
00:50:51,033 --> 00:50:52,666
PUPILS:

923
00:50:52,666 --> 00:50:55,500
KULA:
We feel that it's our
responsibility

924
00:50:55,500 --> 00:50:59,400
to build awareness about
geological hazards and risks

925
00:50:59,400 --> 00:51:03,000
that we are exposed to.

926
00:51:03,000 --> 00:51:04,700
NARRATOR:
It's a strategy that

927
00:51:04,700 --> 00:51:07,166
the rest of the world
could learn from.

928
00:51:07,166 --> 00:51:08,900
MAEA:

929
00:51:13,300 --> 00:51:15,633
NARRATOR:
Awareness is a major reason

930
00:51:15,633 --> 00:51:17,533
just three people died in Tonga

931
00:51:17,533 --> 00:51:20,266
during
the Hunga volcano disaster.

932
00:51:20,266 --> 00:51:23,300
BORRERO:
The death toll was so low

933
00:51:23,300 --> 00:51:26,266
because of the knowledge
of tsunami.

934
00:51:26,266 --> 00:51:27,633
Everybody moved to high ground,

935
00:51:27,633 --> 00:51:29,033
they alerted their neighbors,

936
00:51:29,033 --> 00:51:31,033
they alerted their friends,
and everybody evacuated.

937
00:51:31,033 --> 00:51:33,433
It's miraculous,

938
00:51:33,433 --> 00:51:35,566
but it's doing the right thing
at the right time.

939
00:51:35,566 --> 00:51:41,200
♪ ♪

940
00:51:41,200 --> 00:51:42,733
KULA:
Our existence today is

941
00:51:42,733 --> 00:51:44,933
a demonstration of
our resilience.

942
00:51:44,933 --> 00:51:47,800
♪ ♪

943
00:51:47,800 --> 00:51:51,800
And I think knowledge
will increase the resilience

944
00:51:51,800 --> 00:51:54,100
of the people in the world.

945
00:51:54,100 --> 00:51:55,833
(crowd cheering)

946
00:51:55,833 --> 00:51:57,833
NARRATOR:
Being ready

947
00:51:57,833 --> 00:52:01,766
is Tonga's lesson
for the rest of the planet.

948
00:52:01,766 --> 00:52:03,666
(cheering)

949
00:52:20,800 --> 00:52:28,333
♪ ♪

950
00:52:32,166 --> 00:52:39,700
♪ ♪

951
00:52:41,333 --> 00:52:48,866
♪ ♪

952
00:52:50,500 --> 00:52:58,033
♪ ♪

953
00:53:03,833 --> 00:53:11,000
♪ ♪