All language subtitles for Volcanic.Odysseys.Series.2.4of5.Restless.Giants.1080p.HDTV.x264.AAC.MVGroup.org.eng

NARRATOR:
Japan's volcanoes have produced
some of the largest eruptions

our Earth has ever seen.

Those volcanoes remain
active today.

TOM:
It is right now in a very
violent phase of activity.

It has been building up,
and it continues to build up.

So we don't know
what's happening next.

NARRATOR:
Could a series of
earthquakes be setting off

the country's volcanoes?

TOM:
There's an explosion!

Another one, yeah!

NARRATOR:
And could lead to
a massive eruption.

[Explosion]

Nature's power is our planet's
most spectacular show.

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NARRATOR:
Its beauty makes it
an iconic Japanese landmark...

but its near-perfect symmetry
belies its destructive nature.

Mt. Fuji is a
stratovolcano.

Its last major eruption
was 300 years ago,

but it is still active,
and one day will erupt again.

It's a very appropriate symbol
for this island nation.

Japan is prone to
violent earthquakes,

and it has more than
100 active volcanoes.

The country is spread
over three major islands.

Kyushu in the south
is currently the most active.

It has several
massive volcanoes,

including two that are
considered to be among

the world's top five
most dangerous:

Aso and Sakurajima.

Both are serious threats
to the island's population

of 13 million.

This is Sakurajima.

It's located on the
southern tip of Kyushu.

Scientists pay close
attention to this volcano,

and for good reason.

Sakurajima has produced a number
of cataclysmic eruptions

in the past few centuries.

The last was in 1914.

What's especially concerning
is that it sits across

a narrow strait from
the city of Kagoshima

and its 600,000
inhabitants.

A major eruption would put
the city and its people

in serious danger.

Volcanologist and photographer
Dr. Tom Pfeiffer

has come to Sakurajima
just as it's entering

a new phase of
larger eruptions.

His timing is excellent.

Just as he's driving
into Kagoshima,

Sakurajima erupts.

[Explosion]

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TOM:
We're east of Sakurajima,

which had some massive eruptions
earlier today.

The whole northern
and western sector is hazy.

That's actually
the ash plumes.

Reports say the ash
went up to 17,000 feet.

That is more than
5 kilometers altitude

and it's a record number,
I think, for this year.

NARRATOR:
Tom pulls over to get a better
look at this eruption

which is sending a big
ash cloud into the sky.

TOM:
And it's continuing
to spew ash.

And you see all this haze,
that's all ash

which is still dissipating
from the large plumes

emitted earlier.

Apparently it has been--
it is right now

in a very violent phase
of activity.

If you look over
the past months

it has been building up
gradually.

It continues to build up,
apparently.

So we don't know what's
happening next.

[Explosion]

NARRATOR:
Sakurajima has been
in a phase of

nearly continuous eruption
since 1955.

It normally erupts
once or twice a day.

But in the past few weeks,

the frequency of the eruptions
has increased exponentially:

as many as 10-15
times a day,

with ash plumes up to
five times larger than usual.

Scientists still can't predict
the timing of a major eruption.

But they are afraid that
this volcano is building up

to something major.

An eruption similar in magnitude
to 1914 could be devastating.

It could potentially destroy
the city of Kagoshima.

TOM:
From here you get the sense of
how close Kagoshima City

is actually to the volcano.

Volcanologists know that the
volcano has been inflating

gradually ever since
the 1914 eruption,

and it has reached
the same level as it had

before the last
big eruption.

NARRATOR:
What that means
is that the volcano

has replenished itself enough
that its magma reservoirs

can produce a major eruption,

something it has done
several times

over the past 600 years.

TOM:
So, it is thought that
it might be actually due

at some point, not necessarily
tomorrow or the next month,

but in the not too distant
future it could be due

for another
larger eruption.

That would clearly
put the city at risk--

particularly of
pyroclastic flows,

if you have an eruption
column that rises,

imagine 15-20 kilometers.

NARRATOR:
That could be catastrophic
for the city.

Large eruption plumes can
collapse under their own weight,

causing a burning hot avalanche
of ash and gas

called a pyroclastic flow.

They are capable of
generating tsunamis

or even traveling
over the water

on a super-heated
layer of steam,

burning everything
in their path.

TOM:
Those pyroclastic flows could
sweep and engulf the whole city.

To evacuate a large city
like Kagoshima

is not an easy task,
clearly.

If you look at the lower slopes
you see this dust floating.

This is ash from
the recent eruptions

that has been blown around
the island.

And people who live there
have that constantly.

Anything you wash, after a day,
is coated with ash.

NARRATOR:
Sakurajima means
'cherry blossom island.'

It was given that fanciful name
because its explosions cover

the volcano in glowing rocks
that resemble a tree in blossom.

Even though Sakurajima
is very active,

travel to the island on which
it sits is still possible.

After Tom takes the ferry over,
he'll be able to drive

to the active Showa crater,
which is on the far side.

But there are hazards.

Getting there means he'll
have to pass right through

the ash cloud.

TOM:
This is clearly where
the plume had passed

that was produced by these big
explosions earlier today.

And in fact you can see a lot of
ash covering the leaves.

Look at the car in front of us
and, you know,

this ash is everywhere.

This can be very heavy if
you have to live here

and this is something
you have every few days.

But people go on living here
and they stick to their place.

They don't want
to give this up.

NARRATOR:
This tourist shop
is as close to the volcano

as Tom can get
and still be safe.

The area beyond it
is off-limits.

TOM:
What we're seeing is
that the eruption is continuing.

With every few seconds
you see jets of material

and lightning now
in the ash plume rising.

And they contribute to this
sustained plume

that reaches 1-2 kilometers
above the vent, and spreads,

and all that Northeastern
sector is under ash fall.

It's quite spectacular,
actually.

NARRATOR:
This is not typical behavior
from Sakurajima,

and it's likely attributed
to a new pulse of magma

coming up from depth
that has lead

to a more sustained
ash eruption.

TOM:
Let's hope the wind stays
as it is,

because we are outside
the ash plume

and we have a clear view
to the crater.

This is great.

Let's pray it
stays like this.

On the other side,
it's miserable now.

You have dust in the air
and ash falling,

and you have to be inside,
lock the windows.

If you're outside,
you'd better wear a face mask.

NARRATOR:
Sakurajima's usual eruptions
are a single blast

that only lasts
a few minutes.

This one has gone on
for several hours.

TOM:
The question is,
could this be a precursor

to a much bigger
eruptive phase?

I don't dare to say.

On the long term, maybe.

NARRATOR:
Although volcanoes can and do
erupt without warning,

most large-scale eruptions
have a build up phase

as more magma is pushed
into the system.

As this is happening, there
are many localized effects,

like earthquakes,
that can be detected

by high-tech instruments,
or sometimes even felt

by the people living
around the volcano.

TOM:
Before the 1918 eruptions,

there has been a
very marked increase

in earthquake activity.

Visible deformation of the--
inflation of the ground.

The coastline
visibly changed,

and things like this
are expected to happen

as a precursor of another
big eruption,

which would imply
a much greater volume to erupt.

By greater, I mean orders of
magnitude greater:

a hundred times more than
what has happened today.

NARRATOR:
Before the 1914 eruption,

the city of Kagoshima
was rocked by three weeks

of very strong volcanic
earthquakes

that caused a number
of fatalities.

The quakes are triggered when
new magma breaks the ground rock

as it pushes up to
the surface.

TOM:
What interests volcanologists
to study is actually

to have a picture of what is
actually happening underneath.

And understanding what
is happening underneath

might eventually help
to have an idea

about what is
going to happen.

Unfortunately, it is not
very well understood,

and it is extremely difficult
to be sure and certain

what is happening.

NARRATOR:
Scientists don't
fully understand

what triggers
big eruptions.

The current belief is that
once a magma chamber is filled,

as Sakurajima's,
any new large injection

of fresh hot magma
can reinvigorate

the older semi-cooled magma
in the volcano's reservoir.

The heat and pressure
of the new material

can trigger a
large eruption.

Eruptions are limited to the
amount of eruptable magma

within the underground
reservoir.

A big event can virtually
empty that chamber.

Right now, scientists believe
Sakurjima's chamber

has refilled to 90%,

which makes a larger,
1914-size eruption possible.

Or it can erupt moderately
like we are seeing here,

gradually reducing
the pressure within.

That scenario could mean that
a major eruption is less likely

since the volcano can't
build up enough pressure.

NARRATOR:
The other concern is that
these smaller eruptions

can also open the conduit that
connects to the magma chamber.

If that happens, the result
is like popping the cork

on a champagne bottle.

The eruption can
then sustain itself

until the magma chamber
is virtually empty.

That scenario could
happen quickly

with little very little
advance warning.

TOM:
Sounds like a thunderstorm
in the distance.

NARRATOR:
The activity is spectacular,
but today, at least,

is not the precursor
to a larger eruption.

Things wind down
as the night goes on.

But after dark, Tom can see
a glow within the crater.

That confirms that the magma
is able to push

all the way to the opening
of the crater vent.

By morning the ash emission
has nearly stopped.

It's not over--
the volcano is recharging

before it begins
another eruptive phase.

The cycle that Sakurajima
is going through

is considered high, but still
in the realm of normal.

In Japan, the news of
Sakurajima's increasing activity

is watched closely
by an anxious population.

What has touched off public fear
is that several volcanoes

have become active
at the same time--

volcanoes that have been quiet
for decades or centuries.

They're the latest reminders
of just how geologically active

the country is.

In 2011, Japan was rocked by
a major earthquake and tsunami

and the subsequent meltdown
at the Fukushima nuclear plant.

More than 19,000
people died,

and the entire area
was evacuated.

The Tahoku quake was
a national trauma

that has increased awareness
and raised alarm

about the potential of
more natural disasters.

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NARRATOR:
And in 2014,
50 people were killed

when Mount Ontake erupted
suddenly and without warning.

The eruption sent a
pyroclastic flow

down the mountain,
killing unsuspecting hikers.

On top of that, Hakone,
the volcano closest to Tokyo,

has been raised to
alert level 3 out of 5

after thousands of
small earthquakes

and a sharp increase in heat
was recorded at the summit.

There are fears that
it too may soon erupt.

The Japanese media gives these
stories prominent coverage.

The population wants
to know the government

and its civil defense force
have plans in place

in case of another disaster.

While Tom is
exploring Sakurajima,

a major eruption happens
several hours south.

Mount Shindake, on the
Island of Kuchinoarbujima,

erupts violently, sending a
huge ash cloud into the sky

and triggering a potentially
dangerous pyroclastic flow.

The eruption was caught
on a government web camera

and it shows the sudden
horrifying nature

of the explosion.

This powerful eruption could
have had dire consequences,

but luckily the island
had few inhabitants.

There were only
two injuries.

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NARRATOR:
Eruptions of this
magnitude are infrequent,

so Tom has left Sakurajima

and is traveling by ferry
to Yakashima,

the island directly across
from the eruption.

If conditions are right,

it will give him
an excellent place

to see the aftermath
of the eruption

and to see how Japan responds
to a volcanic crisis.

Japanese media has descended
on the local police station

that has become the command
center for the disaster.

[Reporter speaking Japanese]

TOM:
Yesterday about this time,
a very large explosion occurred

on the neighboring island
of Kuchinoarbujima.

It was an incredible, large,
unexpected explosion

that forced the evacuation
of the whole island.

We see lots of TV crews.

They're all covering
this story,

which is the headline
all over Japan.

I bet nobody expected
it to be that large.

It produced an eruption
column 9 kilometers high,

which spread out,
and the base of the column

part of the ejected material
immediately collapsed

and caused a violent
pyroclastic flow

which fortunately didn't
go through exactly

the populated area,
it seems.

But it was very close.

It illustrates
a bit the problem,

if you live on an active
volcanic island,

in case of a large eruption
like the one yesterday,

there are not many places
you can go and hide.

NARRATOR:
Tom heads to the lighthouse
at Nagata Cape.

It's the closest point to
Kuchinoarbujima Island

and is the best vantage point
to see the volcano.

But bad weather and the
heavy concentration

of airborne ash
from the eruption

have reduced visibility
considerably.

Tom can't see the volcano.

TOM:
Unfortunately, the
island is, of course,

and it makes sense,
off-limits.

And the weather
is not cooperating.

We can't even see it.

But we gave it a try.

In case there would be
another eruption

you should be able
to see the plume,

and maybe in clear weather
you can even see the island.

It's already quite
a bit of luck

to be in the vicinity
of this event.

NARRATOR:
The media is focusing on
questioning if these volcanoes

are becoming more active
because the of the Tahoku quake.

TOM:
It has always
been questioned,

and many people
tend to think

that there must be
a correlation between

earthquake activity
and volcanic activity.

And in fact, there is
probably some relation

but it's currently not
even well understood.

NARRATOR:
To a volcanologist,
this eruption is another chance

to study the phenomena
up close.

But for a nation still
shaken by the earthquake

and tsunami at Tohuko,
this large eruption

once again raises
collective fears.

Japan is a very
geologically active country.

On a relatively
small landmass,

it has more than
100 active volcanoes.

Japan's abundant earthquakes
and volcanoes

can be explained by the science
of plate tectonics.

The Earth's surface
is broken up into

just over a dozen
large sections or plates.

They are constantly moving,

at about the rate
a fingernail grows.

When two plates collide,
the denser of the two

is forced under the other
and back into the earth.

The place where they meet
is called a subduction zone.

As the denser plate descends,
friction causes stress to build

to the breaking point.

It slips suddenly,
causing an earthquake,

and sometimes a tsunami.

As the denser subducting
plate is forced downwards

into the hot mantle
the water and sediments

that are pulled down with it
begin to boil off.

This lowers the melting point,

and the rock around begins
to melt, creating magma.

The more buoyant magma
rises towards the surface.

Japan is the result of
a major subduction zone.

TOM:
You have to consider that
it is only roughly 50 years

that the whole concept
of plate tectonics

has been accepted,

and it is still a science
really in evolution.

NARRATOR:
For now, it's a theory that
scientists can test against.

TOM:
Right now, of course,
each major earthquake,

each volcanic eruption
provides a new opportunity.

You can test your
previous models.

You have a fresh case.

As science advances
and monitoring techniques--

instruments become more refined,
you have the ability

to measure and
detect more subtle changes

that you would not be able
to see maybe five years ago,

as technology constantly
improves.

But it's not very easy to
establish a rule to say

"We have a big earthquake,

so for sure we will have
volcanic eruptions."

NARRATOR:
At this point it is unlikely
Mt. Shindake will erupt again.

So Tom spends time observing
how the emergency response team

is handling the situation.

Japan has been
sharpening its skills

when it comes to
disaster response.

Within hours
of the eruption,

the island was
completely evacuated.

By the end of the day mobile
command centers had been set up

around the island
to relay information

back to their operation
headquarters.

Tom is with a just
a few members of the

Kagashima Civil Protection
Communications division.

This is the same team
that would be responsible

for an eruption
of Sakurajima.

TOM:
This island is approximately
150 kilometers away,

and it's in a
quite remote area,

so they're doing
an amazing job.

They're showing us the
camera that they had

on the helicopter
who arrived on the scene

just 40 minutes
after the eruption.

Then the main team followed
right afterwards

and is now based here.

And yeah, they are here,
and it shows--

it's quite impressive to see
the level of alertness

of the Japanese authorities

in response to a
volcanic crisis.

NARRATOR:
The teams are equipped
to relay video and data

in real-time back to the
command center in Kagoshima.

All of this can be packed
and loaded on a helicopter

and be on site
within an hour.

Their vehicles are equipped
with generators

capable of powering
a small village.

TOM:
In this case, it was
a small island

with approximately
150 inhabitants.

Now you have to of course
try to imagine what you would do

in the case of an eruption
at Sakurajima of that scale,

where you have 700,000 people
living in the city.

NARRATOR:
The eruption was powerful.

It will likely
be rated a VEI-3

on the Volcanic
Explosivity Index.

The Civil Protection Force
will remain in place

for several weeks in case
there is a secondary eruption.

The response to this explosion
was swift and effective.

No lives were lost.

It's another chance for this
unit to hone its technique,

because in Japan
the question isn't

will there be another
eruption, but when.

TOM:
I think if any country
is really preparing

for worst-case scenarios,
a large explosion of Sakurajima,

Japan is probably the best
prepared on a global scale.

NARRATOR:
Tom heads back to Kagoshima
to explore a sleeping giant

so massive that its
potential threat

is almost impossible
to comprehend.

This is the explosive center
of an ancient volcano,

so massive that
this entire area,

including part of the city
of Kagoshima and Sakurajima,

are sitting above
a giant magma chamber.

Deep beneath the waters
of Kagoshima Bay

is a much bigger menace...

the giant Aira Caldera.

TOM:
The entire city literally
sits inside a volcano.

You can see the cliffs
over there.

It goes all around,

from about 24 kilometers
by 18 kilometers,

a rectangular area,
that is the caldera.

It's probably the worst
place for a city to be.

NARRATOR:
A caldera is a feature
that happens

after an eruption empties
the magma chamber

and the ground above
collapses into it.

The eruption of Aira Caldera
took place 22,000 years ago,

and in the years since,

there hasn't been a
bigger eruption on Earth.

Its effects can be found
all around the bay.

TOM:
This hill, "Shiroyama," means
"white mountain," literally.

Shiro, white;
yama, mountain.

White, you can see why;
it's full of pumice.

The white pieces
of pumice and fine ash.

It's the same material
as pumice,

and darker fragments.

Geologists call this
a non-welded ignimbrite.

It's the result of a massive--
a giant volcanic eruption.

This is just a tiny part
of the deposit.

The whole cliff is probably
100-200 meters high.

It's composed of
this material.

And in fact, this eruption
was so large

it deposited pumice and ash
all over Japan.

NARRATOR:
The eruption was so massive
it was believed to be

200 times the scale of
the 1980 eruption

of Mt. St. Helens
in the United States.

Mt. St. Helens sent a huge
ash cloud into the air

so big that deposits
were found in 11 states

and five Canadian provinces.

It was rated as
a VEI-5 eruption

and one of the largest
in recent times.

Eruptions are measured
using the VEI

or Volcanic Explosivity Index.

They're based on the amount
of material ejected

and the height of
the ash plume.

The scale ranges
from 1 to 8.

VEI-1 is gentle.

VEI-8 is mega-colossal.

Each successive number is
10 times greater in scale

than the previous.

An eruption is classified
from start to stop.

The current eruption phase
of Sakurajima

has lasted more
than 70 years

for a total combined rating
of of VEI-3.

Compare this to
Sakurajima's 1914 eruption,

which lasted just eight months,
was rated VEI-4.

Aira's caldera eruption
ranks as super-colossal,

between VEI-7 and VEI-8.

An eruption of this magnitude

hasn't happened in
recorded history.

The closest is the 1812 eruption
of Tambora in Indonesia,

which was a VEI-7.

That eruption killed
92,000 people

and caused widespread
crop failures throughout Europe

that lasted several years.

The Aira eruption
22,000 years ago

was eight times
more massive than that.

TOM:
This massive giant eruption

or if you want to call it a
super-volcano eruption,

a super eruption,
had a result

that the crust of the Earth
sank several hundred meters

forming what is called
the "Aira Caldera,"

and then a large 24x18
kilometer caldera formed.

This whole city actually
sits inside the Aira volcano.

Aira volcano is the whole
complex, the whole caldera.

We are here on the rim;

we are looking down
onto the city.

This is the crater floor.

NARRATOR:
A super eruption
is fed by the build-up

of a lot of magma
in the volcano's reservoir.

Plate tectonics
explains how that works.

Instead of two plates
colliding,

where one sub-ducts
under the other,

around Japan several smaller
micro plates are being crushed,

twisted, and pulled.

This movement has made the
Earth's crust very thin

under the island of Kyushu.

To make matters worse,
the direction and speed

of the sub-ducting plate has
created a convection current

that is producing an anomaly
called a mantle wedge.

This brings superheated
magma even closer

to the surface, where it
reacts with ground water

to lower the melting point
of the overlying rock layers.

It's the volcanic equivalent
of the perfect storm.

The higher temperatures of
the mantle material allows for

a lot more magma to be produced
at shallower depths.

It creates conditions for
massive eruptions.

This is what's happening
under Japan's Kyushu Island...

and why the island is
littered with active

and very dangerous volcanoes,
including Aira.

Although Sakurajima
appears to be a volcano

within a volcano,
they are one and the same.

Sakurajima is a vent of Aira,
but has its own magma reservoir,

but that reservoir draws
its magma from Aira's.

That is one of the reasons
it can produce large

VEI-4 to 5 eruptions
every 100-200 years.

TOM:
The whole island of Sakurajima
is actually

two overlapping
stratovolcanoes,

An older one, Kita-dake,
to the left,

and the young one,
presently active Minami-dake.

All this has grown just within
the past 25,000 years,

so this is really an
incredibly active volcano.

It is one out of the ten
most active in the earth,

I would say, at the moment.

It is definitely Japan's
most active one.

NARRATOR:
Scientists still don't
fully understand what triggers

a caldera eruption.

This is where the massive
reservoir erupts.

During Sakurajima's 1914
eruption the entire caldera

dropped by almost
two feet lengths

proving that the two
magma chambers are connected.

But the big and
unanswerable question is,

is that enough to
destabilize Aira Caldera?

For the people of Kagoshima,
the good news is

that super eruptions
are infrequent.

Such a massive blast
requires long periods

between eruptions to rebuild
the intense volume

of molten material
within the magma chamber.

That process takes many
thousands of years.

Over the past 300,000 years
there have been several

massive caldera eruptions
on the island of Kyushu

at 20,000-40,000
year intervals.

The volcano that is most likely
to produce a caldera eruption,

and in a more advanced stage
of recharging,

is Aso Caldera.

Aso Caldera is not just
bigger than Aira's,

it's one of the biggest
on the planet.

It is ranked as one of the
most dangerous volcanoes

in the world.

TOM:
This caldera belongs to
the XL class of calderas.

There are not that many
in the whole planet

that have been active

in the past few hundreds
of thousands of years.

Maybe you can count them in
terms of dozens.

NARRATOR:
Aso sits directly over the apex
of the mantle wedge.

Here the crust is also
the thinnest in Kyushu

and Aso has produced four
large caldera eruptions.

Three of them happened within
30,000 years of each other.

On a geological timescale,
that is very close together.

The last one was
90,000 years ago.

Aso also contains a
geological feature

called a resurgent dome.

This is where inflation
from the magma chamber

pushes the caldera
floor upwards,

indicating a charged
magma chamber.

It's estimated that the
volume of new magma

coming into Aso's reservoirs
is so great

that it is capable of producing
a VEI-7 eruption

every 10,000 years.

It has been recharging
for 90,000 years,

so it's capable of something
massive any time.

But over the past
20,000 years

its activity has been
relatively small,

and the impact of its eruptions
has been localized.

There are five major peaks
and 17 cones.

One of them, Mt. Nakadake
is still active.

TOM:
This bluish haze,
it's very typical

if there's SO2 gas present.

That is very typical
if magma is actually

very close to the vent.

So I suspect the eruption
is still going on.

It is just right now
maybe a bit quiet,

but it could produce
explosions any time.

Of course, if a sudden
explosion occurs

it's extremely hazardous,

and in fact,
people in the past

unfortunately have been killed
by projectiles.

NARRATOR:
The SO2, or sulfur dioxide gas,
is toxic and an obvious danger.

In fact, Aso has a history of
small but deadly incidents.

Two people were killed in 1979
from a sudden explosion

that caught everyone
off-guard.

Eleven others were injured
when a rock crashed through

the roof of a
bombproof shelter.

Tourists had been able
to take a cable car

to the crater,

but that was suspended
just over two years ago,

when the volcano alert level
was raised to 3.

Tom is going to get
a rare view.

He has arranged
special permission

with government officials
to visit the active crater.

The current eruptive crater
of Nakadake

has seven vents that have
erupted in historical times.

You can tell how active
a volcano is

by how quickly
it builds new mass.

TOM:
Very large,
extremely active volcano,

Remember, all these mountains
with all these cones,

it's just the central part
of the much larger complex,

and it's only
90,000 years old,

which is in geologic terms
almost nothing.

So for a volcano
it's still very young,

a very young age.

Wow, yeah...
It's a very impressive crater.

You have no idea when
you're down there;

it looks so flat
and harmless.

But this is
actually something.

Wow, yeah, incredible.

Wow.

Okay, we are there.

It's impressive.

The Nakadake crater
is all this, actually.

It goes on over there.

It is more than a
kilometer long in total.

It has seven
different vents,

out of which we see
two here that are active.

You hear the roaring,

so there is a very intense
degassing going on.

Magma is very close
to the surface.

Explosions could actually
occur any time.

Number 2 crater
is also active.

There's a lot of
degassing going on.

It's not so much steam,
but apparently lots of SO2.

This bluish haze
is created by SO2.

We're almost out of
the plume,

but you still can smell
sulfur now.

Wind is swirling a bit.

We're at the edge
of this haze.

So I guess if we were
right in the plume

we'd probably need the
gas mask to breathe.

NARRATOR:
The gases coming off the plume
are deadly.

In 1997, three people
were killed on this spot

when they were overcome
by the noxious gas.

TOM:
Nobody can predict whether
it will just gradually

calm down now in the coming
weeks and months,

or it might re-intensify.

A couple of months ago
you could almost see

constant Strombolian
activity.

At least from the webcam.
I wasn't here, of course.

So you would have seen
incandescent pieces of lava

being ejected, and they
piled up to form that cone.

NARRATOR:
Up until recently,
the crater contained a lake.

But the water boiled off
because of the extreme heat.

Water from the surrounding
hill drains into the crater,

making this volcano
unpredictable.

TOM:
I find this is
extremely impressive.

The contrast couldn't be...

There's an explosion!

Explosion!

This is a phreato, maybe
phreatomagmatic explosion.

You see the ash?

NARRATOR:
The eruption is a result
of ground water

coming into contact
with hot magma.

It flashes to steam.

As a gas it expands to more
than 1,200 times its volume

in a sudden explosion.

Much of the plume
is water vapor.

TOM:
You could probably see
stones being ejected.

This was a very small one,

but well,
that was fantastic!

Another one, yeah.

TOM:
You see the black fingers
of ash,

followed by white steam.

This is very typical for
phreatomagmatic explosions.

[LOUD EXPLOSIONS]

TOM:
It's easy to be
killed here.

If this volcano
was not monitored,

if there was free access

you would have
hundreds of people maybe

on a good day,
walking around here.

And then, of course,
the more people there are

on the rim,
the more likely it is

that during an explosion
there could be an incident.

And during daylight especially
they're not glowing,

you have very little chance
to escape them.

Even the hard hat
would not--

it gives protection against
small things,

but if you have a block
like this the hat is useless.

Imagine this 100 times bigger,
and we'd be in trouble.

For me this was
absolutely amazing.

NARRATOR:
Although the eruption
was small and not threatening,

the situation has now become
unpredictable.

The officials have asked
everyone to leave.

TOM:
The best way to decrease risk
is to limit the time

in a hazardous place.

So we've seen two really nice
small explosions,

so we don't want to risk
to get to a bigger one,

which could happen.

So that's legitimate.

They know the volcano,
and they don't want to go

and take us to any
higher risk levels.

So I completely understand.

NARRATOR:
Large caldera volcanoes work
on a geological clock,

taking tens of thousands
of years

to ready themselves
for a major eruption.

And in those terms,
Aso either be could be

overdue for a
caldera eruption,

or it could still could be
thousands of years off.

Given its size and history
Aso is capable of producing

a massive eruption.

Everything in its danger zone
could be wiped out,

including Kumamoto City,
which is downslope

from the volcano.

In recent history, the only
eruption we can relate it to

is the 1991 eruption of
Mt. Pinatubo

in the Philippines.

It was the largest eruption
to affect a populated area

in the 20th century,
with a ranking of VEI-6.

It caused incredible devastation
to the surrounding area.

The ash fall was recorded in
places as far away as Vietnam,

Cambodia, and Malaysia.

That eruption was an
important landmark.

It was the first time that
scientists were able

to predict the eruption in time
to do mass evacuations.

Because of that, the death toll
was under 1,000.

But if history repeats itself

Aso would be on a
vastly larger scale.

What they'd be looking at
would be 40-50 times bigger

than Pinatubo.

This type of eruption can't be
planned for or mitigated.

The ash fall alone
would be so huge

that it would affect
all of Japan.

Its impact would be global.

But hopefully it isn't something
humans have to deal with

for thousands of years.

♪♪♪

NARRATOR:
Back at Sakurajima, that
volcano's explosive activity

has continued to ramp up.

TOM:
Five to ten years ago
it was maybe an average

of one eruption, two.

Maybe on a good day
there were two per day.

There has been a clear increase
over the past years, though,

so it's not unusual now
to have maybe up to ten

during phases of
elevated activity.

NARRATOR:
It's likely that Sakurajima

is building to
a larger eruption.

And that could mean
something in the range

of a VEI-4 or VEI-5 eruption
in the not-too-distant future.

TOM:
This year alone has
produced more explosions

than last year combined,
and we're only in May.

Nobody can predict what the
volcano is going to do,

but it may be a
long-term precursor

to a major phase of
activity again.

[Explosion]

♪♪♪

NARRATOR:
Tom came to Japan just
in time to catch Sakurajima

at its most spectacular
period of activity in years.

TOM:
Sakurajima has put on
a great show for us.

We've seen tremendous
explosions,

small and large.

This beautiful bay
with fishing boats...

I've never seen Sakurajima
so active before.

[WAVES SPLASHING ON BEACH]

♪♪♪

NARRATOR:
Japan has no choice
but to grapple with giants.

From the sea floor
to its tallest peaks,

the country is at the mercy

of the most elemental
geological forces.

These forces have
created an environment

of staggering beauty,

but they've also caused
devastating disasters.

Science is still on
a steep learning curve

when it comes volcanoes,

but with each new eruption
they are beginning to understand

the incredibly complex forces
that are at work

beneath our
Earth's surface.

Knowledge that is teaching
them how to predict

large eruptions
before they happen.

In a country riddled
with active volcanoes,

some of which erupt
on a daily basis,

life goes on for Japan's
nearly 130 million people.

What else can be done in the
face of such powerful forces,

except watch and wait...

and hope that we learn
what we need to

before our geological
time runs out.

♪♪♪

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