All language subtitles for BBC.Dangerous.Earth.Series1.2of6.Volcano.720p.HDTV.x264.AAC.MVGroup.org.eng

Our planet is home to some
spectacular natural wonders.

Yet exactly how and why they
form is still a mystery.

But now, new camera technologies are
revealing their inner workings

in stunning detail.

My name is Dr Helen Czerski

and I'll be looking at how
these extraordinary images

are transforming our
understanding of the natural world.

In this programme, we look at
the latest scientific insights

into the destructive power
of volcanoes.

A volcano is a place where the fiery
innards of the Earth intrude

into our world, here on the surface.

And they're a reminder of the
dynamic nature of the earth

beneath our feet.

Now, thermal imaging is revealing
why eruptions can last months

or even years.

High-speed cameras are showing us
why certain volcanoes

wreak more havoc than others...

..and eyewitness footage captured
on mobile phones

is giving us vital clues as
to why some eruptions

are almost impossible to predict.

We can now catch on camera
the complex processes crucial

to knowing how
and when these forces of nature

are going to blow.

In September 2014, a sunny
Saturday morning hike

suddenly turned deadly for hundreds
of visitors on Japan's Mount Ontake.

With almost no warning,
the volcano erupted,

spewing forth billowing ash clouds,
travelling too fast to outrun.

This mobile phone footage
captured by hiker

Kuroda Terutoshi...

..shows the terror of the tourists
trapped on the mountain.

He and his friends scramble down the
mountain, looking for shelter.

But within seconds,
they're enveloped by the ash cloud

and small rocks from the eruption
are raining down around them.

With no warning is issued, hundreds
of people were in danger.

Rescue operations quickly
swung into action.

Kuroda and many others
had a lucky escape.

But 58 people lost their
lives that day,

most through falling rocks
or gas inhalation.

It was the worst volcanic disaster
in Japan for 90 years.

Ontake has been closely
monitored since the 1980s.

So across Japan,
the question was asked,

why wasn't this eruption predicted?

There's a vital clue in
Kuroda's footage.

The colour of the ash cloud
is almost white,

indicating that it's not
magma being erupted.

Instead, what we're seeing is
steam.

The eruption on Mount Ontake
was a rare event

called a phreatic eruption -
it's a steam explosion.

It happens when groundwater seeps
into the volcano

and meets really hot rock.

It's similar to when you pour water
on to a pan of really hot oil

and it starts to spit and steam.

Inside the volcano, when the water
reaches the very hot rock,

it evaporates to form steam,
and then, as it expands,

it pushes out on the rocks around
it with explosive force,

making a really violent eruption.

They're very hard to predict
because they happen so quickly.

So it's just as well that there
aren't very many of them.

To predict an eruption,

you need to understand what's going
on deep below the surface.

Nowhere more so than at
Nyiragongo in East Africa...

..where a million people live
in the volcano's shadow.

During the last eruption in 2002,

lava flows destroyed much
of the town.

147 people were killed and
thousands left homeless.

Nyiragongo is so deadly because its
lava is the fastest in the world,

travelling at up to 60kmh and
decimating everything in its path.

In recent years, many scientists,
like Dario Tedesco,

have been studying the lava,

trying to understand why
it flows so fast

and whether future eruptions
can be predicted.

It's really completely different
from other volcanoes.

It really is unique.

There are so many secrets on this
volcano that you don't get from

the other volcanoes.

And Nyiragongo offers a
unique opportunity

because sitting in its crater
is the world's largest lava lake.

Usually magma, the molten rock
inside a volcano

collects in reservoirs far below
the earth's surface,

where it's almost
impossible to study.

But here, it's sitting right
out in the open.

Dario's team are trying to collect a
sample of fresh lava from the lake

but it's a long way down.

The crater is deep enough to bury
the Empire State Building.

They stop halfway.

As the lake is so active,

they decide to get a sample from
a safer distance 600 metres away.

But while they're setting up,

Dario spots someone else much
closer to the boiling hot lake.

It is dangerous, in my opinion.

It is a little crazy.

I mean, I won't do that.

It seems an extraordinary risk.

But back in the lab,

analysis of samples like these by
geologist Tom Darrah is giving real

insight into why it's so deadly.

The composition of Mount Nyiragongo
lavas are both complex

and mysterious.

The lava I'm holding my hand from
Mount Nyiragongo

is effectively a time capsule
of the Earth's history.

When the sample is heated
and analysed,

scientists discover a composition
of the chemicals strontium

and neodymium, that's only found
in one other place...

..ancient asteroids.

They think this lava contains traces
of the ancient rocks that formed

the Earth four billion years ago.

The only way it could have this
signature is if its origins lie deep

within the planet.

The gases that we analysed tell us
that this volcano is sourced

from a very deep
location within the Earth.

The source has to be somewhere
well below the Earth's crust.

In fact, scientists believe there's
a huge upwelling of intense heat,

a mantle plume, rising up from
deep under this part of East Africa.

It's the way this hot spot interacts
with the Earth's mantle

that generates a magma that's
very low in silica.

And it's this unusual composition
that makes Nyiragongo's lava

so fluid and so deadly.

With further study of the lava,

they hope to find ways to predict
how the next eruption will happen

and where the lava might flow.

How dangerous an eruption is depends
on the composition of the magma.

There are two main types
of eruption.

If it's effusive, the magma rises up
and flows out as liquid lava.

But in an explosive eruption,

the magma breaks into tiny fragments
of hot ash that explode violently

out of the top.

Explosive eruptions cause far
more volcanic deaths,

while effusive eruptions can
destroy homes and property.

So knowing which type to
expect is critical.

And that comes down to changes deep
underground at a micro scale.

It may sound surprising but one of
the things that's most important

for volcanic eruptions is
the presence of bubbles.

Inside a volcano, there are gases
from deep in the Earth's mantle

dissolved in the liquid magma.

But as the magma rises up,
the pressure drops and bubbles form.

It's like what happens when you take
a bottle of fizzy water

and take the lid off. Because you're
reducing the pressure,

lots of bubbles suddenly form
and they rise up to the surface

because they're less dense than
the fluid around them.

But while these bubbles
are just pushing gas

and a little bit of water
out with them,

in a volcano, they're
driving out red-hot magma.

How much magma comes out and whether
you get a gentle effusive eruption

or a violent explosive eruption

depends mainly on
the magma's viscosity.

And I can show you the effect
that the viscosity has

using these two bottles of fluid.

This one is fizzy water, with lots
of dissolved gas inside it.

This one is lemonade and
it's got sugar in it as well,

which means that it's still got the
same dissolved gas in it

but it's thicker, it's more viscous.

These sweets are going to act as
nucleation sites,

so places for the bubbles to form.

So I'm going to drop these into
the bottles and have a look at what

happens. So I drop them in...

You can see that lots
of bubbles form.

The bubbles are rising because
they're less dense.

They're quite big. They dragged
a little bit of fluid up with them.

This one is similar to
an effusive eruption.

But there's a big difference in what
happens if I do the same thing

with the more viscous fluid.

Drop in these...

and you can see that things
are much more violent.

The bubbles are much, much smaller.

They've dragged loads and loads
of liquid up with them.

It's all escaped from the bottle and
because the liquid is more viscous,

the bubbles find it harder to escape
from it and they drag more of

the liquid up with them
when they escape

and this is the equivalent of
an explosive eruption,

when you have much
more viscous magma.

In 2010, an explosive eruption in
Iceland wreaked far more havoc

than anyone had predicted.

Eyjafjallajokull spewed
thousands of tonnes of ash,

up to 10km into the
atmosphere and out across Europe.

But it was no ordinary ash.

For the first time in British
aviation history,

all flights into and out of
the UK have been cancelled.

The particles were so fine they
could blow into aircraft engines

and melt, causing potentially
fatal breakdowns.

Fears over the ash led to the
biggest shutdown of airspace

since the Second World War.

100,000 flights were grounded
and millions of passengers stranded.

The Icelandic eruption wasn't
particularly big or powerful.

So why was it one of the most
disruptive in living memory?

Volcanologist Emma Liu
thinks the answer lies with
how the ash was formed.

The reason Eyjafjallajokull's
eruption caused so much disruption

was because of how much fine grain
volcanic ash it produced.

Normally when this type of
magma erupts,

it produces something like
you see in Hawaii.

You get large particles like this,
which don't travel very far.

I have actually some ash from
the Eyjafjallajokull eruption.

You can see it's very fine
grained, like a powder.

The thing that was different is that
this volcano erupted

from beneath the glacier.

The magma was able to mix with cold
water from the glacier

and it's this interaction that
caused the magma to cool

much more quickly.

Volcanic ash is actually a glass,

a volcanic glass created when
molten magma cools to a solid.

But as Emma has been discovering,
when glass is cooled quickly,

it behaves in a very unusual way.

So this is a Prince Rupert's Drop.

They've been known since
the 17th century,

when King Charles II was given
one of these drops by his nephew,

Prince Rupert of Bavaria.

It's formed by dripping molten
glass into water.

When the glass cools
quickly in water,

the outside of the drop cools very
fast, forming a hard outer shell.

But the inside,
it cools more slowly,

and as it cools, it contracts,

pulling in on the outer shell,
like stretching an elastic band.

So we think that what happens when
the glass is cooled quickly

to form a Prince Rupert's Drop,

it's similar to what happens when
magma is cooled rapidly

when it comes into contact
with water, like glacier ice

or lakes. All this stored energy
inside the drop

gives it very unusual
fracture properties.

You can hammer...

..and it still won't break.

But it has a weak point.

It's only by using
an ultra-high speed camera,

filming at 130,000 frames
per second,

that we can see just
what's happening.

By breaking the tail and releasing
all the stored energy very quickly,

and you can see when
the glass exploded,

it produced this very fine powder,

which is just like the volcanic ash
that would have been released

into the atmosphere.

Using an electron microscope,

Emma can compare particles from
the Prince Rupert's Drop

with ash from Eyjafjallajokull.

So both are very angular,
very blocky in shape.

They show the same beautiful,
brittle fracture patterns,

which tell you a lot about how
the fracture actually formed.

The similarities between the natural
ash particles and the fragments

of a Prince Rupert's Drop suggest
they were formed in similar ways.

Emma's work could be crucial
in understanding

what will make some future eruptions
so much more dangerous than others.

This is a map of every active
volcano in the world.

Some of them, like Hawaii,

are thought to sit over mantle
plumes like Mount Nyiragongo,

but most active volcanoes in
the world sit at subduction zones,

and those are places where one
tectonic plate

is sliding underneath another one,

and you get a line of volcanoes
along the back.

And that's the case, for example,
down the western coast
of South America, here,

where the plate's sliding
underneath South America.

And when you look at the whole of
the Pacific, you can see a pattern.

There's a ring of volcanoes
all the way around here.

This is where 75% of the world's
active volcanoes are

because this is where the most
subduction zones are.

And it's called the
Pacific Ring of Fire.

Papua New Guinea's Mount Tavurvur
sits right inside this ring of fire.

In 2014,

holiday-maker Phil McNamara was
filming the volcano when he caught

on camera the extraordinary power
of an explosive eruption.

Watch out for the shock,
it's coming.

CRACKING

Holy smoking Toledos!

This incredible footage has been
seen more than 18 million
times online.

It shows this volcano explosively
erupting and the lovely thing

about it is, you can see the shock,

you can see the pressure wave that's
travelling out as the air that's

pushed out from the volcano barrels
into the air in front of it

so quickly.

The pressurised magma inside the
volcano exploded so violently

that it compressed
the atmosphere around it

and that's the line you can see
expanding out.

And that pressure front is
travelling faster than
the speed of sound,

but even though it's
travelling so quickly,

it still takes time to reach
the holiday-maker on the boat.

Watch out for the
shock, it's coming.

CRACKING
There it is, all that time to
come this distance.

Holy smoking Toledos!

The Tavurvur eruption
was over in days

but some eruptions last for months

or longer. Now, new camera advances
are helping reveal why.

In 2011, Puyehue-Cordon Caulle
in Chile

erupted for the first time
in 50 years.

The plume was 14km high

and thousands of local residents
had to be evacuated.

But six months later,
it was still erupting.

And volcanologist Hugh Tuffen
joined an expedition

led by John Castro
to find out more.

I just had to get out there.

It was a unique opportunity, as this
was a very rare type of eruption.

My specialism is rhyolitic magma.

We almost never watch rhyolitic
eruptions taking place.

There's actually only been two
worldwide in my whole lifetime.

The jungle they trekked through,
normally lush and green,

was covered in ash
from the eruption.

But it was the lava that Hugh
was most interested in.

It was the first time in our lives
that we'd ever seen a rhyolitic lava

flow in action.

This was an amazing thing.

Rhyolite is very, very thick viscous
magma that is rich in silica.

Its viscosity makes this lava
the slowest moving on earth,

travelling just a few metres a day.

This was as far from a river of red
lava as you could get.

This was like a glacier of creaking
and groaning lava that was almost

imperceptibly moving.

Because the volcanic gases become
trapped in this thick magma,

rhyolitic eruptions are some
of the largest on earth.

Whoa! That was like textbook.

And Hugh believed it might also
explain something else.

One of the unsolved mysteries
of rhyolites

is how the gas escapes from
this very, very thick magma.

There has to be some way of
the gas getting out.

If they could discover how
the gas escaped,

they might be able to work out how
long the eruptions would last -

crucial information for the
thousands of people living nearby.

One night, as he was filming the
expedition, Hugh had a revelation.

It gradually got darker and
darker, and as it did so,

then the vent really came to life.

I had a switch on the camera which
meant that we could go from watching

visible light to infrared light.

We could suddenly see bombs of lava
that were being ejected on these

long lazy paths before they
landed on the ground.

The thermal cameras saw through
the steam and vapour

and showed the hot bombs
as bright white pixels.

But it also showed them stopping
and starting in cycles.

It seemed as though there
were valves

through which gas and ash was able
to escape very rapidly.

But then these were blocking up.

And then a new valve was opening
up right next to it.

Wow, look.
It's just cleared itself again now.

It was a beautiful thing to watch,
but also very scientifically useful,

as we can then work out how fast
the bombs are moving

and this all links in

to how the gas is able to escape
from the magma at the vent.

Hugh's thermal imaging had revealed
that after each ejection of bombs,

the volcanic vents were sealing up
again, trapping the gases inside.

And that's why the eruptions
lasted so long.

To actually see all these secrets
being revealed by Puyehue

was quite something.

Around the world, hi-tech cameras
are giving us new insights

into how volcanoes work.

Stromboli in Italy is one of the
most active volcanoes on earth,

spewing forth ash and steam daily.

But it's also emitting a gas
called sulphur dioxide.

It's a crucial indicator
of volcanic activity.

But it's completely invisible
to the naked eye.

Now, scientists from Manchester are
using an ultraviolet camera that can

see these invisible emissions.

By capturing the gas on camera,

they can work out the total volume
of all the gases emitted,

giving them vital clues as to how
an eruption will evolve

and how long it might last.

At volcanoes like Yasur in Vanuatu,

scientists from Rome are trying to
unlock the secrets of dangerous

high-speed lava bombs.

But because they are ejected
at supersonic speeds,

they've been almost
impossible to study.

Now, by filming at speeds of up
to 1000 frames per second,

the scientists can see their
precise velocity and path.

This gives them critical information

about how far the bombs
might travel...

..and how hazardous the eruption
might be for anyone living
in its path.

The difficulty with studying
volcanoes is you don't know

when they're going to be active,

so it's very difficult to be
there at the right time.

And that's why cameras are
now an essential tool

for studying volcanoes, because
they can be there all the time.

There's plenty of data like this.

This is live data from Kilauea
volcano in Hawaii

and there's lots
of different webcams,

there's thermal images
showing the crater,

there's overviews of the crater,
lots of different angles,

and this is broadcast in real-time
to scientists around the world,

so they can watch what's happening,
and even better than that,

if something interesting
does happen,

they can then go back and look at
what led up to that event.

So there's a video here from the
last 48 hours of the same volcano

and you can see that
as daylight comes,

the activity of the volcano
changes with time.

And it's data like this that's going
to be essential in the future

for taking the next step in
understanding these connections

to the innards of our planet.

Volcanoes have long been feared
as fiery and unpredictable demons.

But now we're seeing very intricate
details and invisible processes

as never before, our knowledge
is improving rapidly.

They still hold many secrets but
we are coming closer than ever

to understanding how they work
and when they're going to erupt.