[music playing] NARRATOR: Earth, a 4.5
billion year old planet, still evolving. As continents shift and
clash, volcanoes erupt, and glaciers grow and recede. The Earth's crust is carved in
numerous and fascinating ways, leaving a trail of
geological mysteries behind. In this episode, Krakatoa,
one of the deadliest volcanoes in the world. [music playing] More than 100 years
ago, it erupted with such devastating
fury that it wiped itself off the face of the Earth. In the process, it sent
out the loudest sound in recorded history, and
killed more than 36,000 people. And now, this deadly
volcanic beast is back. Geologists investigate one of
the world's fastest growing volcanoes to hunt for clues
that will tell them if and when Krakatoa will explode once
again with the same cataclysmic force. As they pries apart the
rocks, the answers they find will be another piece of the
puzzle of "How the Earth Was Made." [music playing] Krakatoa is one of the
most dangerous volcanoes the world has ever seen. When it exploded apart
in 1883, the blast was heard over nearly 10%
of the Earth's surface. It was a worldwide clarion call
announcing the awesome power of volcanoes. The site of this
monstrous eruption lies between the Indonesian
islands of Java and Sumatra, in a channel known
as the Sunda Straits. Today, a new volcano
has staked its claim in exactly the same spot. It's called Anak Krakatau,
meaning the child of Krakatoa. Right now, it's in the middle
of a new and extremely dangerous phase. Dr. Charles Mandeville
traveled here to see if the child will one
day be as deadly as its parent, to see if history is
about to repeat itself. The stakes are high. At risk now are the one million
people of Java and Sumatra who live within 50
miles of the volcano. Oh, wow, look at that. We get a little
explosion going on. I've kind of been following
this from the internet from my office, but it's
actually good to kind of see the thing live again. I've noticed in coming here that
the volcano itself has grown possibly as much as 250 to 300
feet since the last time I've actually stood on its
crater back in 1990. NARRATOR: Growing at a
rate of 12 feet a year, the 1,033 foot volcano is both
one of the fastest growing and youngest volcanoes
on the planet. This remarkable footage
shows its explosive birth in June, 1927 when it first
broke through the seafloor and erupted out of the water. Its rapid growth is clear
evidence that this new volcano is extremely active. But will it be as
deadly as its parent? [music playing] These eruptions are always
accompanied by a series of ground-shaking tremors. For geologists, these
small earthquakes are evidence that this volcano
is entering a more destructive phase. Seismographs have been buried
deep on Anak's slopes to record this underground activity. But these small quakes are not
the only sign of a dangerously active volcano. A more subtle clue is right
beneath Mandeville's feet. Black sand beaches are very
common in volcanic areas. The minerals and the glass
fragments that comprise the ash that the volcano erupts
is typically dark charcoal gray-colored, and usually,
these materials don't stand up to weathering over
long, protracted periods of geologic time,
but you find them in relatively
fresh, pristine form when you're near
an active volcano. NARRATOR: Anak Krakatau is
rarely completely quiet, but the level of
activity in 2008 shows that the volcano has
become unusually violent. To discover just
how much of a threat it could pose in
the near future, volcano detectives must
turn to their history books to learn what made its parent,
Krakatoa, so destructive. This is a story that has
fascinated geologists for over a century. What got me switched
onto volcanology was the 1883 eruption. I learned about this in
school, and I remember thinking how incredible that an
island could just blow itself into oblivion, and
what was going on? What was that all about? What was special? How does that happen, and
could it happen again elsewhere on Earth? [music playing] NARRATOR: Before it
exploded in 1883, Krakatoa was an uninhabited
island with three jagged peaks covered in lush vegetation. It was part of the
Dutch East Indies, a thriving, bustling hub
of international trade. Indonesia's wealth of
minerals and spices attracted many Western traders,
journalists, and geologists. Their reports provide
firsthand accounts of what happened before
and during Krakatoa's deadly and shocking eruption. There had been no hint
of volcanic activity in anyone's memory. No one had a clue that
Krakatoa was about to blow. Beneath its green
and placid surface, Krakatoa was a time
bomb waiting to explode. So the first idea the locals
would have got that anything was-- anything strange was
happening on their island would have been in May, 1883,
earthquakes, earth tremors. [music playing] NARRATOR: These tremors reached
as far as the capital, Batavia, more than 100 miles away. Few suspected that the
island of Krakatoa, seen on the distant
horizon, was to blame, and that these earthquakes
were the first clue to its deadly potential. [music playing, ground rumbling] Then, on May 20, 1883,
Krakatoa announced that it was no mere island. One of Krakatoa's three peaks
exploded with extreme force, shooting a plume of ash
hundreds of feet into the air. But after these
initial fireworks, the activity appeared to cease. The local population
breathed a sigh of relief. Thinking it's safe. The governor of the
Dutch East Indies sent a research party of
geologists to the island in late May, where they
observed the scorched landscape and smoking crater
with amazement. Their meticulous report
gives modern day geologists the first clue as to what
lay behind Krakatoa's immense power. A key discovery was a
layer of pumice 1 foot deep that covered the
island's shores. This pumice is the
solidified lava that comes from the
heart of a volcano, and it's riddled with bubbles. These bubbles suggest to
geologists that Krakatoa is a strata volcano. And those volcanoes tend
to be the classic volcanoes that you see in textbooks. They're very steep-sided, like
some sharp, almost triangulos, like mountains. NARRATOR: These are the most
dangerous types of volcanoes on Earth. They are fueled by molten rock
called lava, known as magma when it's underground. The magma that flows
through these volcanoes is like liquid dynamite. Strata volcanoes are dangerous
because of the sorts of lava that they erupt. And the lava comes out of
strata volcanoes is very sticky, viscous lava, and
the danger there is that the sticky lava often
contains large amounts of gas. NARRATOR: The bubbles inside the
pumice discovered on Krakatoa in 1883 show that
the magma was once packed with explosive gases. Because the magma was so sticky,
a term describing its thickness and resistance to flow, the
gas could not easily escape. The formation of gas
bubbles in the sticky lava can be powerful enough to
actually rip the lava apart, and in the process, you
actually tearaway the volcano. The whole thing becomes-- becomes explosive, and
you produce very dangerous volcanic activity. NARRATOR: Krakatoa's magma
had another deadly property. NICK PETFORD: In
some situations, the lava can become
so sticky that it sort of freezes up and congests
or chokes up the volcano. It forms a kind of
a plug or a seal. What will happen is that over
time, more magma is coming up and being trapped beneath that
plug, sometime in the future, the pressure would be so
great, there would be so much magma wanted to get up that you
would just rip the plug apart, and that can produce, again, a
catastrophic volcanic eruption. NARRATOR: This is exactly what
happened at Krakatoa on May 20, 1883. From then onwards,
over the summer, it quietened down a bit, but
this is really the kind of calm before the storm. NARRATOR: The investigation
into Krakatoa's deadly potential has produced important evidence. The frequent earthquakes
on Anak Krakatau today indicate the volcano
is still dangerous. The pumice from 1883 reveals
that Krakatoa was a strata volcano, its sticky, gas-rich
lava making it dangerously explosive. Krakatoa's eruption
in May, 1883, was spectacular, but beneath
the surface, Krakatoa was refueling. An even greater eruption
was gathering force out of sight and out of mind. Anak Krakatau is one of the
fastest growing volcanoes in the world. Geologists are investigating
its threat to the region. They have turned to the
past to uncover what made its parents so deadly. [music playing] In 1883, exactly 100 days
after Krakatoa first blew, the volcano showed
its true power. This final phase of eruptions
began at six minutes past 1:00 on the
afternoon of August 26. [music playing, ground rumbling] All three volcanic peaks
erupted simultaneously, hurling dense clouds of ash and
smoke an astonishing 17 miles into the sky. The eruption of Krakatoa
was one of the biggest volcanic events of the
last few hundred years, and it would have been-- to people observing
it, it would have been like the beginning of the
end of the world, if you like. NARRATOR: The power
of this eruption was immense, like a giant
jet engine aimed skywards. The air quickly became choked
with tons of thick black ash blotting out the Sun. The temperature, because of
all the ash in the atmosphere, would be stifling, and
if you were very near, on the, for example, the
west coast of Java, you-- you could get the ash in
your throat and in the eyes. It would have been a
real vision of hell. NARRATOR: And a nightmare that
showed no signs of ending. By the next morning
of August 27, 1883, Krakatoa's three
craters had been raging for more than 14 hours. Then, sometime between
5:30 and 10:02 AM, the land was deafened by a
series of four huge explosions. The noise was so loud
it could be heard over 2,000 miles away in the
Australian desert near Perth. The third was the loudest
recorded noise in history, the equivalent to 200 megatons
of TNT, 13,000 times the size of the bomb that
destroyed Hiroshima. What created this
awesome explosion? The hunt for answers takes
geologist Charles Mandeville to the jagged island of Rakata. This tiny island
is, in fact, a part of the once mighty Krakatoa. CHARLES MANDEVILLE: The
record of what the volcano did from May 20 to August
26 to 27 is here represented on the islands
by the layered deposits that we see preserved
in the jungle. This is a gold mine for
a volcanologist trying to reconstruct the events
that took place here, because each one
of these deposits tells us something particular
about what the volcano was doing. NARRATOR: This pumice was thrown
out of the heart of the volcano in 1883. Mandeville believes that it
holds the key to understanding the forces that
destroyed Krakatoa. What I have in my hand is
a mixed pumice or streaked pumice, and what
it represents is that we had two magmas mingling
in the conduit of the 1883 eruption of Krakatoa. [music playing] NARRATOR: The stripes are
proof of the two types of magma inside Krakatoa. The lighter band represents
the cooler, gas-rich magma that was present during the
earlier eruption in May. This eruption only partially
emptied the magma chamber. By August, this void was filled
from deep below by searingly hot dark-colored magma. When these two magmas
mixed together, it was a lethal cocktail. The intense heat
of the dark magma caused the huge amounts of
gas within the light magma to expand. The magma chamber that
was holding this mixed bag became over pressurized to
the point where it exceeded the rock strength of
the roof rocks above it, and when that happens, you
can get really rapid ascent of magma to the surface. NARRATOR: When this magma
exploded from the surface, it ripped apart tons of rocks
with an ear-splitting blast. This mega explosion
caused the loudest noise in recorded history. The striped pumice on Rakata
proves that magma mixing was the trigger, but Krakatoa
wasn't just the loudest volcano in history, it was a killer. Because Krakatoa
itself was uninhabited, some of the volcanoes
first victims were at Ketimbang, a village on
the southern coast of Sumatra. But Ketimbang is on
the mainland, 20 miles from Krakatoa, and separated
by the waters of the Sunda Straits. How these people fell victim to
the deadly ashes was a mystery. To uncover the answers,
we have to return to the scene of
the crime, Rakata, and to these imposing
white cliffs. They may seem part of
an ancient landscape, but these 200-foot white
cliffs were laid down in a matter of hours. They are what's left of a raging
torrent of hot gas and rocks, a terrifying force of nature
known as a pyroclastic flow. Pyroclastic flows
travel extremely quickly, so you can outrun them. They're also extremely hot,
several degrees centigrade, so they will-- if you're caught in
the middle of one, they will incinerate
you instantly. [music playing] NARRATOR: Perhaps the
most famous victims of a pyroclastic flow lie at
Pompeii, the Roman settlement that was utterly destroyed
during the eruption of Vesuvius in Italy in the year 79. The perfectly preserved
remains of the people here are testament to the power
of these fiery avalanches. And most people die
not because 100% burns, but because they
inhale the gases, which are so hot that they just
destroy the-- the air passage and the lungs instantly. And so after two
breaths, you're dead. NARRATOR: The sheer size
of the cliffs at Rakata have led geologists to estimate
that the pyroclastic flows thrown out by Krakatoa were
an amazing 2,800 feet high. But the victims of
this deadly torrent were on the other side
of the Sunda Straits. What happened next
was truly astonishing. Pyroclastic flows
are ground-hugging. In other words, they-- they
follow the ground's surface as they go down. But they also have an upper
part which is very rich in gas, so it's low density. Now, when a pyroclastic
flow hits the sea, the dense bit carries on
down onto the ocean bed, but the gas bits
are still very hot. It goes hurtling
across, scooting across the top of the water. There's virtually no friction
between the gas and the water, so it could travel a
very long distance. NARRATOR: Over 2,000
people at Ketimbang perished from the burning
debris that could not just walk on water, but
run at amazing speeds of up to 200 miles per hour
across 20 miles of open sea. The investigation into
the Krakatoa volcano has pinpointed the
extraordinary force that ripped the island apart. Striped pumice is proof
that magma mixing created the vast explosion. 200 foot cliffs on
the island of Rakata are evidence of vast
pyroclastic flows, big enough to cross the ocean and claim
the volcano's first victims. But contemporary reports show
that most of Krakatoa's victims were not killed by
these deadly avalanches, but by a very different
force of nature. [ground rumbling, music playing] August, 1883, Krakatoa's second
and most deadly eruption. More than 2,000
people were killed by searingly hot
pyroclastic flows. But there was worse to come. These gigantic boulders are
on the shore of Anyar in Java, 22 miles away from Krakatoa. They are a crucial clue to
what the volcano did here, and a stark reminder of what
could one day happen again. They are made of coral, which
can only grow underwater, so some immense force
unleashed by Krakatoa must have put them here. These shattered bricks
are another piece of the same puzzle. They are all that remain of a
lighthouse that once was one of the sturdiest buildings
on the Java coastline. But no match for Krakatoa. I'm standing at the top of
the new lighthouse in Anyar, 120 feet above sea level, built
two years after the eruption of Krakatoa in 1883. The old lighthouse down there is
nothing but a trace of bricks, because it was wiped
out by a large tsunami. NARRATOR: Eyewitness accounts
detail the exact height of this terrifying wave. Difficult though it
might be to comprehend, the momentum of that wave
would have taken the water up to the level that
I'm now standing. NARRATOR: Krakatoa's
death throes had triggered a massive
wall of water that now raced towards the shore at Anyar. I don't think anybody living
along the shores of Western Java or southern Sumatra would
have known about the tsunami that they were about to face. And certainly, nobody would
have been able to survive those sorts of wave heights. NARRATOR: The power of the wave
can be seen in this 600 ton block of coral that was
ripped from the seabed and smashed the
lighthouse to pieces. Still here today, it provides
some of the clearest evidence of the immense power of
Krakatoa's 1883 eruption. The same wave that
shifted this boulder also destroyed houses,
villages, and transport, leaving nothing but
twisted wreckage behind. The mighty wave even picked up
and stranded a Dutch steamer, The Berouw, 2 miles inland. [music playing] This immense tsunami
claimed the lives of more than 34,000 people. It's quite possible
that those people who lived in the villages in Western
Java and southern Sumatra thought, well, the volcano's
out there somewhere. It's an island. So it can't possibly
affect us here. But of course, the eruption
itself triggered the tsunami, which meant that the water
adjacent to the volcano was being displaced right
across to where they lived. So you know, that-- that feeling of safety
was-- was sadly misplaced. NARRATOR: For modern
day investigators, the puzzle was how fire and
water had combined to wipe out an entire region. The evidence came from
the shattered remains of the volcano
itself, Rakata Island, part of one of Krakatoa's
three original peaks. Its sheer vertical cliff
face tells volcano detectives about Krakatoa's final moments. When you have a very
large volcanic eruption, you evacuate a lot of
magma, it leaves behind, effectively, a hole. So quite often, the crust just
collapses down into that hole, and that leaves behind
what we call a caldera. NARRATOR: Krakatoa had ejected
such vast amounts of burning magma and rock it could
no longer support itself. Drain away the water, and we can
see how it collapsed, creating an immense caldera. So this cliff behind me marks
the edge of the 1883 caldera. Under the boat, this water
depth is about 40 times as deep as most of
the area around us. The scale of this
collapse is pretty big. It formed a caldera
that's about 3 miles in the north-south
direction, by about 5 miles in the east-west direction. NARRATOR: This immense
collapse has only occurred once in recorded human history. The combined weight
and power of Krakatoa's awesome pyroclastic flows
and this huge collapse was more than enough
to trigger the tsunami. The riddle of just
what had caused Krakatoa's tremendous tsunamis
had finally been solved. When the smoke had cleared
and the waters receded from the most devastating
eruption in recorded history, the island of
Krakatoa had vanished. In total, Krakatoa had
killed 36,417 men, women, and children. It was, without doubt, one of
the most dangerous volcanoes in history. [music playing] But while investigating
the 1883 eruption, scientists discovered ancient
lava flows hidden in the jungle and on the seabed, this deadly
volcano had struck before. But when scientists dated the
lava flows, they hit a problem. Radiocarbon dating was only
able to place the eruption to between the 1st
and 13th centuries, a spread of 1,200 years. Scientists needed
more information in order to try and shed
light on a new Krakatoa threat and help the hundreds of
thousands of people living in the area. The trail of
evidence at Krakatoa had gone cold, literally. Because thousands of miles
away from the sweltering heat of Indonesia, in the frozen
wastes of the Antarctic, scientists recently
discovered a critical clue to Krakatoa's explosive past. Ice cores are cylinders of ice
that we drill from the ice caps in Greenland and Antarctica. You can look at
things like volcanoes. Any material coming from
the surrounding oceans make its way to Antarctica,
where we can detect it in the ice. You might imagine that we
see the dust and the ash from a volcano. In fact, very little of that
from the big Indonesian type volcanoes ever makes
it to Antarctica. So what we do see
is sulfuric acid. Big volcanoes, they spew
out a lot of sulfur dioxide into the atmosphere,
which is oxidized into the sulfuric acid, which
we then measure in the ice. NARRATOR: The sulfuric acid
cannot be seen in the ice cores with the naked eye, but can only
be detected back at the British Antarctic Survey's lab,
where the cores are kept at a continuous minus
13 degrees Fahrenheit. [music playing] So this is a piece of
core from Antarctica. This is a piece from
James Ross Island. It's about 10,000
years old, this ice. What we're doing now is
measuring the volcanic signals. And what we see is
very, very distinct, clear, electrical pulses that
come from the sulfuric acid from the volcanoes. So very quickly, we can
see all the volcano signals throughout the whole core NARRATOR: One of the strongest
signals found in the ice cores is from the 1883
eruption of Krakatoa. What we could see
from the 1883 eruption, we can't see the ash, but
we can see a very large peak in sulfuric acid. In fact, it's one of
the biggest peaks we've got in the last 1,000 years. It's such a big peak, in fact,
that we use it to date the ice cores, because it's like a
reference horizon we can see there. NARRATOR: Each ice core is like
a diary of the Earth's climate. Each layer of ice
represents one year. In the same way that we
can count tree rings, scientists can count
back each layer of ice to determine the exact
date of any eruption. Counting back from
the 1883 signal, there is a huge spike in
the sulfuric acid levels in the year 535. This is clear evidence
of an enormous eruption during the dying days
of the Roman Empire, an eruption far greater
than Krakatoa's in 1883. We are now beginning
to come to the conclusion that, yes, there was a large
volcanic eruption in 535. In fact, it looks one of the
biggest ones on the record in terms of how much
sulfuric acid it put into the atmosphere. NARRATOR: The ice cores tell
us a lot about this mystery volcano. Its eruption was so enormous
that its impact was global. Its date falls
exactly in the middle of the time span of the
lava flows around Rakata. Could it be Krakatoa? The clues seem to fit. If they are the same
eruption, this is evidence that Krakatoa has a far more
deadly past, and potentially, a far more deadly future. Can we tell where
it's come from Krakatoa? No, that's more difficult.
We can see it in Antarctica, and we can see it in
Greenland, so that tells us it was probably
somewhere mid latitude, so somewhere around
about the equator, maybe. So it's a possibility, but
we cannot really pin it down at the moment. NARRATOR: Despite
this uncertainty, there is no doubt of Krakatoa's
capacity for destruction. The steep cliffs at Rakata
show that Krakatoa collapsed to form an enormous caldera,
triggering a deadly tsunami. And yet, ice cores
from Antarctica suggest that Krakatoa may have
exploded before, with even more force than 1883. To discover what originally
created not only 1883 Krakatoa, but also, the current
Anak Krakatau, scientists will have to travel even
further back in time some two million years. [music playing] The source of
Krakatoa's awesome power remained a mystery to
scientists for centuries. One clue is its location. Indonesia contains
more volcanoes than anywhere else on Earth. Indonesia is a jackpot
for volcanologists, simply because the evidence of
volcanic centers that may have lasted several million years
are available and ready for observation and study. NARRATOR: Incredibly, there
are 21 these fire mountains on the island of Java alone,
an area of the same size as New York state. The National Park of
Tengger Bromo in East Java is one of Indonesia's most
active volcanic zones. To view a landscape
like this is actually humbling, because it tells
us that there are forces that work that far exceed anything
that mankind can construct. NARRATOR: But why there should
be so many volcanoes in such a small area no
one could explain. A key discovery
was that Indonesia lies adjacent to the
notorious Ring of Fire, a chain of volcanoes stretching
around the entire Pacific Ocean. In the 1950s. American geologist Harry
Hess began research into the groundbreaking
hypothesis known as seafloor spreading. This laid the foundation
for plate tectonics. Plate tectonics is
based on the idea that our planet is not a
perfect and unbroken sphere. It's composed of eight major
tectonic plates that jostle and jar against one another. These plates are driven by
heat from the planet's core. [music playing] Here, in Indonesia, the plates
collide faster than almost anywhere else on Earth. The volcanoes here are created
when the heavier oceanic plate is pushed under the
lighter continental rock. This is subduction. When the rock is pushed deeper,
it melts to produce magma. Over thousands of years, it
builds up into a vast magma chamber many miles beneath
the surface of the Earth. Eventually, the pressure
of the extra magma becomes too great for
the Earth's crust. The magma forces its way up
to the surface in a storm of hot ash and boiling lava. A volcano is born. In the case of Indonesia, this
is a nation constructed almost entirely from volcanoes. Most of Indonesia is, in
fact, composed of volcanoes that initiated from somewhere
down below sea level, rose up to sea level,
and then grew as islands and amalgamated to form bigger
landmasses that now comprise the Indonesian nation. NARRATOR: Using the
theory of plate tectonics, scientists can rewind the clock. 45 million years ago,
the Australian plate started to move north rapidly. The island chain
of Indonesia began to emerge from the
ocean at the point where the two plates collided. Vast numbers of
volcanoes exploded as the Australian
plate was pushed deep into the bowels of the Earth. Krakatoa was a product
of these same forces. And it was two
million years ago, as our early human
ancestors were taking their first tentative
steps, that the volcano was created. So the fact that under the
Sunda Straits of Indonesia, you have all these
processes taking place 70 and 80 miles down below the
surface made it inevitable that a volcano like Krakatoa
came into existence, but also, had a
catastrophic eruption. NARRATOR: What made Krakatoa
so much more dangerous than hundreds of other
volcanoes in Indonesia only became clear in 1988. Scientists discovered that
large clusters of earthquakes were taking place beneath
the Sunda Straits. Earthquakes are common
along plate boundaries, but this amount
was off the charts. This major clue would enable
scientists to finally identify the killer factor in Krakatoa. [music playing] Beneath Krakatoa, in the
middle of the Sunda Straits, the subduction zone
contains a kink. This twists and rips
the Earth's crust and provides even more material
to fuel Krakatoa's hungry magma chamber. Where you have those kinks,
two things could happen. Firstly, there might be a
greater chance of earthquakes because the kink itself
actually starts to tear or rip, and secondly, where the kink
is might generate more melting, and it's the melting that
takes place in the mantle that ultimately leads to the lavas
erupting from the volcanoes at the surface. NARRATOR: Finally, the origins
of Krakatoa had been revealed. Hundreds of volcanoes
in Indonesia show that the country lies
on a volatile plate boundary. Unusually high
numbers of quakes show that Krakatoa lies on a
deadly kink within this zone. But can scientists now use this
knowledge to predict Krakatoa's future, a prediction that is
today more important than ever, because the volcano is back, and
it's getting bigger every day. [music playing] Today, these
shattered islands are all that remain of the
cataclysmic 1883 Krakatoa eruption. But a deeper understanding
of this event is now more important than ever,
because out in the straits, a new threat is growing. Krakatoa is back in the
form of Anak Krakatau, Indonesian for
Child of Krakatoa, and that child is now
an angry teenager. Like a phoenix from the
ashes, Anak Krakatau is growing directly over the
site of the original Krakatoa volcano, leading
scientists to conclude it's being fed by the
same magma chamber deep beneath the Sunda Straits. This deadly heritage means
that Anak could potentially be one of the most dangerous
volcanoes on Earth. But just how immediate
is this threat? Since its explosive
beginnings in 1927, Anak has erupted
frequently and violently. As one of the fastest growing
volcanoes on the planet, this 1,033 foot high
mountain bears watching. Predicting exactly when another
major eruption will happen is difficult, but
there are clues. Underground tremors
are a sure sign that the magma deep within the
volcano is starting to move. We have seismometers stationed
on the volcano that tell us when rocks are breaking,
not just at the vent, but in the subsurface, heralding
the arrival of new, fresh magma into the edifice, into the cone. NARRATOR: These details are
transmitted via radio signals to the monitoring station on
the mainland, which is operated 24 hours a day. They have a simple scale to
measure the threat running from 1 to 5. Anything above a 3, and
they go on red alert. At the moment, it's hovering
around the danger zone, a level 3. The type of magma
within the volcano is another way geologists
can judge the potential of a major eruption. But the magma itself
is impossible to test, as it lies several miles
deep within the Earth. The next best clue is to look at
what has been literally thrown out of the volcano, lava bombs. I've got my hand on a basaltic
andesite scoria bomb that was probably blown out of a vent
about 3/4 of a mile from here, and you can imagine to be
hit by one of these would not be a good situation. These can actually
range up to things that are the size of
refrigerators and television sets, and there-- thereby, making them even
more lethal, particularly when they're traveling
at 120 miles an hour. NARRATOR: Mandeville
analyzes these rocks made up of basaltic andesite, which will
give him a clue to the makeup of the magma deep underground. Part of what this composition
tells me is the composition of magmas being erupted at Anak
are unlike what was typically erupted at the 1883
eruption of Krakatoa, which was much more silica-rich
and much lighter in color, typically, light
beige to almost white. NARRATOR: The more silica in
the magma, the more viscous or sticky it is, and that's
what contributed to Krakatoa's explosive eruption in 1883. The explosive gases were
trapped in the magma and pressure had been
building up over time. Fortunately, the dark color
of the lava bombs from Anak Krakatau are evidence that
the magma is low in silica, and the explosive gases have yet
to reach critical 1883 levels. But this is not a
permanent state. Over the years,
a magma like this can, in fact, evolve
into something that was that explosive. NARRATOR: As Anak
Krakatau grows, the magma will certainly
become thicker and stickier. As in its parent, once
the magma gets too sticky, the vent could become blocked. The silence could
signal disaster. It means that pressure
could be building up inside. Too much pressure, and
Indonesia could suffer another cataclysmic explosion. [music playing, ground rumbling] More than 100 years of
investigation into Krakatoa has helped unlock the
secrets of its past, and provided scientists
with strong evidence that Anak Krakatau is
following in its footsteps. The pumice from 1883
suggests that Krakatoa was a deadly strata volcano. The stripes in the pumice show
that the massive 1883 eruption was triggered by an
injection of super hot magma. It was this that blew
the volcano to pieces. The remains of vast
pyroclastic flows that were over twice the
height of the Empire State Building plus the
immense caldera show the massive scale of
Krakatoa's 1883 eruption. But most ominously
of all, the position of Anak Krakatau near the
deadly ring of fire directly above a kink in
the subduction zone means that a future massive
eruption is inevitable. A lot of the Anak Krakatau
activity that we now witness today is actually
almost a continuation of the volcanic activity
that took place back in 1883. We could have another eruption
here on the scale of the 1883 eruption of Krakatoa. NARRATOR: The 1883
eruption of Krakatoa may be the most famous, but
it is a geological certainty that it won't be the last. Krakatoa is on the rise again,
dynamic proof that the Earth is never at rest. [music playing]
