>> 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 countless
and fascinating ways, leaving
a trail of geological
mysteries behind.
Water. One of the most powerful
forces on the planet. It plays a
crucial role in creating life
and destroying it, in forging
landscapes and in breaking apart
the Earth. In its most dramatic
form, it becomes a killer wave
known as a tsunami. Until
recently, predicting when these
monsters may next strike has
been impossible.
But today, scientists are
starting to understand these
giant waves. By connecting clues
as varied as ancient Japanese
writings and landslides, ancient
corals and buried Native
American settlements, the
secrets of tsunamis are finally
being unlocked.
How The Earth Was Made 01x09 Tsunami Original Air Date on April 7, 2009
== sync, corrected by elderman ==
Tsunamis. One of the most deadly
forces of nature. Giant waves
that travel faster than a jet
plane, they can cross entire
oceans in just hours.
They have the power to smash
buildings, vehicles, anything
in their way.
By itself, you wouldn't
think that water just streaming
into the coast would necessarily
cause so much damage. But in
fact, they are very fast moving
and they pick up everything in
its path, so it's not the water
by itself, it's what comes with
the water that is also a part of
the big hazard.
>> A tsunami isn't over in just
a few seconds, it is a torrent
of raging water that keeps
coming.
>> The main thing about a
tsunami is the persistence. It
comes on and on and on, and just
when you think it has to quit,
it keeps coming, and it's the
power plus the--the duration
that is unstoppable, really.
>> Tsunamis have ravaged the
Earth for billions of years.
When the Earth was first
created, the moon was much
closer. It filled the sky.
Its gravitational pull was much
stronger, and it generated
towering waves over half a mile
high that raced across the
primeval oceans.
Oh, my God!
>> Today, tsunamis are still a
threat to coastlines all over
the world.
Tsunamis will always
occur, and have always occurred,
throughout Earth's history. But
it's only been more recently, as
population densities have
increased and people have moved
and migrated to the coastal
regions, that we've become much
more aware of the tsunami
hazards.
>> The investigation into what
caused these monster waves
began over a thousand years ago
on the islands of Japan.
This country is the world's
tsunami hotspot. Its coasts have
been pounded with these enormous
waves more than anywhere else on
the planet. Evidence for this is
the word tsunami itself. It is
Japanese and literally means
"harbor wave".
Japan has the longest written
tsunami record of anywhere in
the world. The records go back
as far as 684 A.D.
By studying these records, it is
possible to work out that, on
average, this country has been
struck nearly every seven years.
Samurai writings speak of people
living on the coasts running
for higher ground as soon as
they felt an earthquake. The
Japanese knew this was a clue, a
warning sign that a deadly
tsunami would soon follow. But,
despite their attempts to
escape, tsunamis have
continually bought death and
destruction to these islands.
In 1896, a wave that hit Honshu
in the northeast claimed the
lives of 27,000 people.
In 1933, the same area was
smashed again. This time, 3,000
people were swept away.
And in 1993, the island of
Okushiri was rocked by an
enormous earthquake measuring
7.8 on the Richter scale.
Buildings were leveled and fires
raged. But worse was to come.
Minutes after the shaking had
subsided, an ominous white
crest appeared on the horizon -
a tsunami. A gigantic wave swept
in, flattening any buildings
still standing.
In Japan, the locals had already
worked out the connections
between earthquakes and
tsunamis. But there's another
hotspot on Earth where tsunamis
regularly strike - the Hawaiian
islands. But very few of them
were preceded by an earthquake.
The city of Hilo on the Big
Island has been dubbed the
Tsunami Capital of the World.
Dozens of these enormous waves
have hit these beautiful
islands, and the mystery is why.
With no natural warning to go
on, the people of Hawaii must
rely on the world's biggest
tsunami monitoring station.
Set up in 1949, it is connected
to a network of buoys spread
across the Pacific Ocean. These
buoys provide important clues.
They monitor changes in sea
level that indicate the
approach of any potential
tsunamis.
In 1960, scientists got the
breakthrough they were looking
for. They were finally able to
work out the type of event at
the root of Hawaii's mystery
tsunamis. An enormous quake on
the coast of Chile, the biggest
recorded of all time, with a
factor 9.5 on the Richter scale,
triggered a tsunami that swept
across the entire Pacific Ocean
in just a few hours. The islands
of Hawaii where thousands of
miles away, directly in its
path. The Tsunami Warning Center
was monitoring its progress,
revealing for the first time
that a single massive wave
crossed thousands of miles of
ocean. The warning center was a
success. They were able to
evacuate the communities closest
to the shore before the wave
struck. But the homes they left
behind were decimated. In Hilo,
the tsunami was so strong it
even bent parking meters in
half. The wave continued past
Hawaii to Japan. It had lost
none of its power. Pacific-wide,
this tsunami cost more than
2,000 lives and caused millions
of dollars' worth of damage.
Devastating as it was, the 1960
event was a turning point in
the study of tsunamis. It was
the first time that scientists
could accurately measure how the
size of an underwater earthquake
directly affected the size of a
tsunami. And conclusive proof
that a tsunami can travel
thousands of miles across the
Earth.
>> And It was with this Chilean
earthquake that we really could
prove that the, uh, undersea
motions associated with the
earthquake are generating these
huge effects.
>> Now scientists had the
evidence to confirm that
undersea earthquakes were
directly responsible for
tsunamis. The ancient Japanese
suspicion was now scientific
fact. In terms of modern tsunami
study, the 1960 wave was year
zero.
The Chilean
earthquake was, you might say,
the perfect storm, it's when
scientific understanding had
advanced to the point where
scientists had begun to see the
link connecting everything, so
it's a new science, we're
talking about something which is
really only less than 50 years
old.
>> There are more tsunamis in
the Pacific Ocean than any
other. So in 2004, the world was
taken by surprise when one of
the largest recorded tsunamis of
all time took place in the
Indian Ocean.
On December 26th, 2004,
Indonesia was rocked by the
second largest recorded
earthquake ever, 9.2 on the
Richter scale.
Minutes later, a 90-foot tsunami
slammed into the Southeast
Asian coastline.
225,000 men, women and children
lost their lives.
The Indonesian earthquake had
as much energy in it as the
total energy consumption in the
United States in one year.
>> This enormous burst of energy
had been released in just
seconds. Once again, the world
had been reminded of the Earth's
awesome power. In the last 50
years, scientists were finally
able to confirm a solid link
between earthquakes and
tsunamis.
By monitoring the size of the
Chilean earthquake in 1960,
scientists were able to prove
conclusively that earthquakes
triggered these gigantic waves.
By following the path of this
tsunami, they were able to
prove that a tsunami could
travel thousands of miles from
its origin.
Monitoring the earthquakes that
cause this incredible
devastation involves looking
many miles underground.
By investigating the power at
the root of these giant waves,
scientists can begin to figure
out when and where these waves
may strike next.
These dramatic pictures of the
aftermath of the 2004 Indian
Ocean tsunami show the havoc a
tsunami can unleash.
It's almost impossible to
imagine something like that
happening here in the Pacific
Northwest. But Professor Brian
Atwater believes that events
like the 2004 tsunami could one
day happen right here too.
He was intrigued by early
settlers' accounts of Native
American folklore tales that
spoke of great waves sweeping
inland. They convinced him that
huge, locally generated tsunamis
have struck here before, and
could strike again, posing a
threat to tens of thousands of
people living on the Pacific
Northwest coast. To find out if
he was right, he needed to
uncover evidence of past giant
waves hidden in this landscape.
To be really sure it's a
tsunami, though, he would also
have to find evidence of the
earthquake that caused it.
Atwater's starting point is the
Copalis River in Washington
State, just a couple of miles
from the long sandy beaches
that make this area a thriving
tourist resort. In the banks of
this estuary lie buried
thousands of years of
history.
This is one of the dirtiest jobs
in science. Hunting for evidence
of earthquakes is a muddy
business, but it's worth it.
Atwater has found signs of a
potential tsunami.
>> There's a clue in this bank
that nature has provided, it's
this notch. And notches like
this are common where tsunamis
have laid out sheets of sand and
then later currents and--and
waves come along and they pluck
the sand grains out of the bank,
but they leave the mud.
>> Atwater has to dig deeper to
find what he is looking for, a
layer of sand that could have
been swept miles inland by a
tsunami.
>> OK, so now you can see the
sand. What deposited this sand?
Maybe it was a tsunami.
>> To prove that this was sand
from a tsunami, Atwater's muddy
quest must continue. He also
needs to find proof that the
land here around the river has
moved up or down - a sure sign
of an earthquake. After some
hard work, Atwater finds what he
has been looking for - clear
evidence of both an earthquake
and a tsunami. This time, there
was a human cost as well.
>> Here we have evidence for
abrupt lowering of land, and we
also have evidence for the
associated tsunami. In this
case, humans are involved - this
was a fishing camp. Here you
have the remains of that fishing
camp in the form of fire-cracked
rocks which were--the rocks were
used to heat water, mainly.
OK, so fishing camp, overrun by
tsunami. Because the land
dropped after the tsunami, the
tides came in and covered the
fishing camp site and made sure
that people wouldn't use it
again.
>> The land the fishing camp was
built on was dragged down
during the earthquake. The
tsunami deposited sand over the
remains, and finally, the tide
covered the settlement with mud,
where it remained undisturbed -
until now. Atwater finally had
the proof he needed. His Native
American myths of giant waves
were no mere legend.
But what was it that caused the
earthquake? The prime suspect
lay 50 miles offshore - the
Cascadia fault. Cascadia is a
major weakness in the Earth's
crust. Although the Earth may
seem to be a solid sphere,
beneath the oceans and
continents it is divided into
eight major and many minor
segments known as tectonic
plates. Where they meet, they
can grind and jostle against
each other at fault lines,
causing earthquakes. Geologists
had long thought that the
Cascadia fault line was
incapable of generating a major
quake. But Atwater's
investigation has proved that it
was highly active. The big worry
for Atwater and the thousands of
people who live in this region
is that the Cascadia fault line
bears an uncanny resemblance to
another highly active fault
line, the Sunda Megathrust.
It was an earthquake along this
fault that was responsible for
the Indian Ocean tsunami that
killed nearly a quarter of a
million people.
>> Where we get two tectonic
plates coming together, such as
the case of the Indonesian
tsunami in 2004, one plate
pushes beneath the other plate
and creates lots and lots of
friction and tension and drags
the upper plate down with it,
and that process can take
hundreds of years, even
thousands of years. It's a very
slow process. But eventually the
pressure of this one trying to
push back up again wins, and it
flips like that.
And that creates a megathrust, a
sudden movement of the seabed,
and that's what creates a
phenomenal tsunami.
>> Two factors made this Sunda
Megathrust earthquake so deadly.
The first was its size. At
factor 9.2 on the Richter scale,
this was the largest in nearly
50 years. The second was that it
took place not far below the
surface.
When we talk about a
megathrust, that's really where
the seabed is disturbed
dramatically. Sometimes, if the
earthquake is deep in the
Earth's crust, then you see very
little surface manifestation of
that earthquake. If it's quite
close to the surface or very
intense, then quite often you'll
see the seabed itself moving,
and that's what creates a
powerful tsunami.
>> Investigating the ocean floor
after the quake revealed that
more than 1,000 miles of
fault line had fractured and
sprung up by 60 feet. This
massive jolt pushed up billions
of tons of water, enough to
cover Manhattan to a depth of
nearly five miles.
>> The rift zone itself was
about a thousand miles long. We
had this entire stretch of
subsea moving, which creates a
huge wave. So the whole thing
was a phenomenal size and
certainly one of the biggest
tsunamis in living memory.
>> Atwater's determined research
showed that the Pacific
Northwest was at risk from this
level of devastation too. But he
didn't want to unnecessarily
alarm the coastal inhabitants
until he had collected all the
evidence he could. Atwater
needed to find out precisely
when this tsunami struck this
coastline to see if there could
be more. He first tried
radiocarbon dating the soil
along the Copalis River. But the
result could only take him so
far. They showed that the
earthquake and tsunami occurred
somewhere between 1680 and 1720.
More importantly, Atwater still
needed precise evidence of how
big it had been.
But so far, his investigation
has uncovered two extraordinary
facts. By unearthing the
abandoned fishing camp, Atwater
could see th a Cascadia
earthquake here had caused the
land to drop. The notch in the
bank was proof that this same
earthquake had generated a
tsunami. But what these clues
didn't tell Atwater was just how
big the tsunami was. He had no
way of pinning down the size of
the threat to the Pacific
Northwest. His investigation was
about to take an unexpected
turn, with clues coming from not
only thousands of miles away,
but also from hundreds of years
ago.
Japan has the oldest record of
tsunamis of anywhere in the
world. Samurai writings told of
a huge tsunami in 1700 that had
swept over the east coast of
Japan. It hit without warning,
and destroyed entire
settlements. Japanese scientists
were baffled as to where this
wave had come from. There had
been no earthquake to warn the
villagers to make for higher
ground. The mystery wave was
dubbed an orphan tsunami.
Back in the U.S., Brian
Atwater's investigation into the
mysterious Cascadia earthquake
and tsunami needed more
evidence. He had no accurate way
to pin down either the size or
the date of the event.
All he knew was that it had
taken place sometime between
1680 and 1720. But Atwater's
dates were a revelation to the
Japanese scientists. Could this
event be the birthplace of their
300-year-old orphan tsunami?
>> And they said, "By the way,
we have this tsunami we've been
trying to, uh, find a home for
in 1700, so we think your--your
earthquake happened in 1700,
specifically in the evening of
the 26th of January 1700, and it
was of magnitude nine."
>> A Cascadia earthquake that
produced a wave with enough
power to cross the entire
Pacific Ocean to Japan would
have had to be a factor nine at
the very least. This is roughly
equivalent to the enormous
Indian Ocean earthquake.
Earthquakes like this have so
much power that they can send a
tsunami across an entire ocean
with ease.
The amount of energy
involved is very hard to
estimate, and it's hard to put
it into sort of terms that
people can understand.
We are looking at the phenomenal
forces of several Hiroshimas,
hundreds of Hiroshimas, in fact.
>> But tsunamis are not just a
very big wave, they're fast.
>> The big difference is the
scale of the wave - it's
typically three or 400 miles
long. It's also not very high -
when it starts off life, it's
usually about two or three foot
high. But it's moving very fast.
It moves at a speed determined
by the water depth. The deeper
the water, the faster it moves,
so in the deep ocean, this wave
is moving at over 500 miles an
hour.
>> Deceptively, as a tsunami
speeds through deep water, it
may appear completely harmless
and scarcely detectable.
Close to shore, the wave becomes
a deadly killer. It is only then
that a tsunami's true power
becomes clear.
>> As the wave gets to shallower
and shallower water, as it
approaches a coastline, the wave
slows down. The shallower the
water, the slower the wave, so
it goes from 500, to 400, to
300, to 200, much, much slower.
The back of the wave is still
going full speed, and so the
whole thing piles up, and that's
why tsunamis are so destructive.
>> It is this immense speed and
power that reveals how events
here in Cascadia could devastate
a coastal village in Japan, how
an earthquake in Chile could
decimate Hawaii, and how the
Indian Ocean earthquake could
kill almost a quarter of a
million people. If a quake like
this happened in Cascadia, the
damage it would do to the
Pacific Northwest coastline
would be catastrophic.
But to be sure about the scale
of this threat, Brian Atwater
has to be 100 percent certain
that the dates of the two
tsunamis were the same.
After fully exploring the
estuary of the Copalis river, he
found one site that might hold
the information he was looking
for - a ghost forest.
>> This spruce root marks the
remains of a forest that
includes the ghost forest behind
us, dropped down into tidewater
during the Cascadia earthquake.
This ghost forest is made up of
the standing dead trunks of
western red cedar, and they were
killed on account of the land
here dropping, and then tides
coming in and surrounding these
trees and bringing in saltwater.
> This area would once have been
covered with a dense forest.
But today, only the bleached
trunks of the rot-resistant
western red cedar remain in
place. When Atwater and expert
tree ring specialists cut them
open and studied the lines of
growth inside, they finally
cracked the 300-year-old tsunami
puzzle.
The dates of the Japanese and
Cascadia events were exactly
the same - January 1700. The
Japanese orphan tsunami finally
had a parent.
>> Maybe there's a certain
amount of justice to it
that--that a place that doesn't
have written records has these
outstanding geological records.
>> The link between the two
events made it certain that the
Cascadia earthquake had been at
least an awesome magnitude nine.
And ominously, it is almost
certainly not the only time that
Cascadia has rocked this area.
Atwater believes he has found
proof of a whole series of
tsunamis stretching back 5,000
years.
Each layer of sand in this
sample represents a separate
tsunami.
>> There are places at Cascadia
where I've seen nine stacked up
in a column about 20 feet long.
Uh, nine buried soils, some of
them coated with little sand
sheets. And--and they, you know,
you--you say, "OK, it's--it's
not a question of if, but it's
just a matter of when."
>> Atwater's tireless detective
work alerted officials to the
increased tsunami threat.
As a result, the towns along the
Washington State coast have
been able to prepare for this
potential catastrophe. If a
Cascadia quake occurred, the
first waves could arrive here in
just 25 minutes. Tsunami warning
signs line the roads, and sirens
stand ready to warn of an
approaching wave. The lives of
thousands of people are safer
thanks to the work of Atwater,
and to some 300-year-old
Japanese writings.
>> This is a hazard that shows
its face often enough for us to
take precautions, to fasten the
seatbelt against it.
>> By dating the ghost forest
along the Copalis River to
precisely 1700, Atwater had the
final proof that Cascadia was
capable of creating a
Pacific-wide tsunami.
Uncovering the multiple layers
of tsunami debris in the
riverbank dating back 5,000
years show that monster waves
have struck here many times.
This is an ongoing threat.
Atwater knows that another
earthquake is due here, but he
has no way of knowing exactly
when. Back in the Indian Ocean,
the site of the world's most
lethal tsunami in 2004, one man
has taken the investigation of
tsunamis to a new level. He
believes that he has found a way
to make the Earth's fault lines
give up their secrets and
accurately predict when the next
deadly tsunami could be on its
way.
The idyllic looking Mentawai
island chain in Indonesia hides
a violent secret, one that makes
it today one of the most
dangerous places on Earth.
These islands lie directly on
top of the Sunda Megathrust,
south of where the enormous
Indian Ocean earthquake
triggered the 2004 tsunami.
The Sunda Megathrust is one of
the largest fault lines on the
planet. Since it caused the
2004 earthquake, it has also
become one of the most
notorious.
Predicting earthquakes here is
tricky, but Professor Kerry
Sieh has a good track record.
He has successfully forecast two
along the Sunda Megathrust
already.
The key to successful tsunami
prediction is to forecast when
and where earthquakes will
strike. And to do this,
scientists must look into the
past.
If you want to answer
questions about earthquakes
that only happen every few
hundred years or few thousand
years, well you've got to find
some--some geological
instrument that allows you to
see those earthquakes.
>> Professor Sieh has found an
unusual way to unlock the
secrets of the Sunda
Megathrust's turbulent history.
Corals. These coral atolls are
built from the limestone
skeletons of millions of tiny
creatures. Each generation
builds on the remains of the
last. Over time, the atoll gets
bigger and bigger. As long as
the corals remain underwater,
they flourish, but once they're
above water, they die.
Earthquakes are responsible for
killing all the coral stranded
above water on this beach.
This beach contains corals of
many different ages. Altogether,
Professor Sieh has nearly a
thousand years of history at his
fingertips. But to unlock the
secret history the corals
contain, he and his team have to
take a less than delicate
approach.
>> We're looking at a sawcut
that we just made through a
coral micro atoll. And the great
thing about this head is it
records a sudden drop of about a
foot and a half down to here. It
died down to here, because the
island rose. The new low tide is
way down here. Everything that
was so bold as to grow up this
high, dies.
>> The shape of the coral
records the fall of the
Mentawai islands as they are
literally pulled down by the
Sunda Megathrust.
But, crucially, the corals also
record the moments when the
islands are thrust up out of the
water during an earthquake.
Between quakes, the islands are
once again pulled down by the
fault in a never-ending cycle.
>> You have to imagine that
rocks actually are elastic. Take
a diviving board, the diver--the
diver walks out on the platform
and it--it bends like this, and
then he jumps and he springs up
and he jumps off. And when he
jumps off, the diving board
doesn't stay here, it doesn't go
like--it doesn't go like this,
you know, the diving board
springs back up, it's elastic.
Well, rocks are the same, rocks
are elastic too, so when the
Indian Plate goes down it pulls
the Sumatran section down too,
and then later, it fails. So it
just springs up like a diving
board.
>> By analyzing corals all over
this beach, Professor Sieh has
discovered a regular pattern to
this cycle. A major earthquake
rocks these islands roughly
every 200 years.
>> What we have here in Sumatra
with the corals is what I call
the Holy Grail of, uh--of
earthquake science, of--of
palaeoseismology, and that is a
long record that has many
cycles in it, a
thousand-year-long history of
earthquakes.
>> But when the geologist looked
even closer, he saw that the
cycle was more complex.
>> When we cut a slab, we can
see it in much more exquisite
detail because we can see what
we call the stratigraphy, or
the--the--the layering and how
the layering relates to the
changes of the tide, so what we
can see over here, then, is the
annual bands of growth, right
here, so there's about ten years
between this earthquake and
this earthquake.
>> Professor Sieh had discovered
a major clue. The corals record
that, not only does a major
earthquake and tsunami hit here
every 200 years, but that they
are always accompanied by a
number of smaller quakes.
This is a cycle within a cycle,
a supercycle.
And by counting back the layers
of growth within the coral, the
geologists can put an exact date
on all of these earthquakes.
>> We know there's a sequence in
the 1350s, 1370s, we know
there's a sequence in the
1560s, 1600s--1600, we know
there's a sequence 1797, 1833.
Those sequences are about 200,
to 200--yeah, 230 years apart.
>> This is crucial information
for the people of the Mentawai
islands, who have no written
history. But Professor Sieh's
work doesn't stop here. By
uncovering their history in the
corals, he believes that he can
now predict the future for these
islands. And he's already had
some success. Professor Sieh
began his work here in 1993, and
soon realized an earthquake was
imminent. The Mentawai islands
were about to start their next
deadly supercycle.
OK! Experienced an
earthquake!
>> In September 2007, he was
proved right, when an earthquake
shook the islands just enough to
generate a small tsunami that
wrecked homes and schools.
History is repeating itself,
exactly as he predicted it
would. A much bigger earthquake
and more dangerous tsunami could
be due any day.
One section hasn't
failed since 1797, so, since
George Washington was President
of the United States. We know
we're now in a sequence of at
least three giant earthquakes,
we're expecting another one. The
question is whether the
earthquake and tsunami will be
in the next 30 minutes or the
next 30 years.
>> Thanks to Sieh's research,
the people of these islands
have had time to prepare. When
the wave comes, they will be
ready.
>> Earthquakes are forecastable.
If you--if you have enough
information about how they've
behaved over the last thousand
years, or two or three or four
cycles, you can really make a
significant forecast that people
living in the area actually can
do something about.
>> Education is key. Children
here are now taught that as soon
as they feel the shaking of an
earthquake, they should run for
higher ground.
Newly built roads snake up steep
hills from waterside villages
to allow rapid escape from the
deadly waves.
>> I'll bet that young children
alive today, if they--certainly
if they live to be 60, they're
gonna see that earthquake. In
fact, I think there's a better
than 50 percent chance that
it'll happen in--within the next
30 years.
>> By analyzing the shape of the
corals on the Mentawai islands,
Sieh has proved that a major
tsunami cycle starts here every
200 years. By dating the lines
within the coral, he can be even
more exact. They show that these
cycles contain not just one, but
several deadly tsunamis. The
Sunda Megathrust is the clear
culprit for tsunamis here. But
not every tsunami is generated
by an earthquake. A rarer,
different type of wave is out
there - a megatsunami.
>> Although earthquakes are by
far the most common cause of
tsunamis, there is another
source for these deadly waves -
landslides. And these tsunamis
have the potential to be so big
that they have been called
megatsunamis. Scientists had
long suspected that waves could
be generated in this way, but
conclusive photographic proof
wasn't available until 1958.
A landslide into Lituya Bay in
Alaska triggered a wave that
reached heights of several
thousand feet.
This footage, shot just after
the tsunami struck, shows the
wave's enormous power. The trees
here once stretched all the way
down to the shores of the bay,
but were ripped off the slopes
by a wall of water, leaving
nothing but bare exposed rock.
The tsunami was generated when a
relatively small earthquake
triggered a single enormous
landslide of rocks and debris
into the bay.
The resulting wave was higher
than the Empire State Building
and stunned scientists around
the world. Tsunamis on this
scale are incredibly rare.
But another megatsunami,
triggered by a rockfall 10,000
times bigger than Lituya Bay,
could be on its way from a
small island across the Atlantic
Ocean.
The Canary Islands, off the
coast of Africa,re formed
from a series of volcanoes.
The youngest is the island of La
Palma. It is formed from two
volcanic ridges. The first is
the extinct Cumbre Nueva to the
north of the island. The
younger, active Cumbre Vieja
lies to the south.
It erupted as recently as 1971.
Geologist Dr. Simon Day's
research was crucial in
developing the La Palma
megatsunami theory. It began
with an unusual rift that had
opened up during a major
volcanic eruption in 1949.
>> We're standing here in the
fault and it runs way down
to the south along the crest of
the volcano for two and a half
miles, so it's one continuous
long structure.
>> Day believes this fault is
evidence of a geological
time bomb, the beginning of a
giant landslide.
>> What we see here to my right
are layers of--of volcanic
rocks, volcanic blocks here and
layers of volcanic ash.
And on the west of the fault, we
see the same layers of blocks
and ash and those, before the
fault moved, were joined up and
then when the fault moved, they
were separated and the rocks to
my left moved down and to the
west. What we think will happen
in some future eruption is that
this fault will have gotten
bigger and the whole of this
western side will slide away in
a giant landslide into the
ocean to create the tsunami.
>> This landslide would send the
entire southwest section of La
Palma, one sixth of the island's
total mass, crashing into the
Atlantic Ocean in a single giant
landslide.
>> What we envisage is the
whole of this coastline and the
slope extending up all the way
to the crest of the volcano that
is now in the clouds, all of
that mass of rock would slide
away in a single massive
landslide into the ocean and
pushing the water up in front of
it to create the tsunami wave.
>> Initially, this wave would be
over 30 times bigger than the
2004 Indian Ocean tsunami, more
than 3,000 feet high.
The 1980 eruption of Mount St.
Helens was proof that a volcano
could collapse in this
terrifying fashion.
This was impressive, but the
collapse of the Cumbre Vieja
would be 200 times the volume of
this.
1,200 billion tons of rock would
hurtle towards the ocean at top
speed.
The resulting wave would head
straight out into the Atlantic.
That wave, of course,
would then spread out and
separate out into smaller waves,
but even so, after crossing the
Atlantic and piling up again on,
for example, the eastern
seaboard of the United States or
in the Caribbean or in northern
Brazil, the waves there, we
predict, would still be between
30 and 100 feet high. So that's
as large as, if not larger, than
the tsunami that struck Sumatra
in 2004.
>> Boston...
New York...
and even Miami could all be
under threat from the giant
waves.
This was a bold prediction. Day
needed more evidence to back up
his theory. As he was about to
see, the rift in La Palma's
landscape was far worse than he
expected. The 1949 eruption had
left a different type of
geological scar on the island.
Evidence of a more serious
weakness within La Palma came
from a series of eerie looking
lava flows dotted across the
island.
>> One of the characteristics of
the 1949 eruption that's unusual
is that, instead of starting at
one vent and just continuing
there, a series of volcanic
vents opened up in different
parts of the island.
>> When Day plotted these
weaknesses on a map, he came to
a frightening conclusion. The
rift was far bigger than he had
first suspected.
>> The area that's potentially
affected is very much greater
than the length of the fault at
the crest of the volcano would
indicate, extending out, um, ten
or 15 miles from the crest out
to sea.
>> This growing body of evidence
proved that the rift wasn't
just a mere crack in the surface
of La Palma, but a deep fissure
that reached hundreds of feet
down into the island's
foundations. It is La Palma's
volcanic heritage that is the
key to this tsunami threat.
>> The big hazard here isn't the
eruptions themselves, it's the
fact that the volcano is
building up and building up
over time and becoming more and
more unstable, so that will
eventually lead to a collapse.
>> And it seems that this is not
the first time a La Palma
eruption may have triggered a
giant landslide. Proof lies in
the north of the island in these
sheer cliff faces, formed
65,000 years ago.
>> What we see in the north of
La Palma is the landslide scar
left when the old volcano in the
north of La Palma experienced a
giant collapse and produced a
giant landslide off to the west.
So that was a huge collapse - it
removed as much as 100 cubic
miles of rock and deposited it
out into the ocean, so it's the
sort of event that we think is
going to happen again in the
future at the--at the Cumbre
Vieja.
>> This ancient collapse of the
old Cumbre Nueva volcano is
almost certain to have generated
a gigantic wave.
And the next collapse might not
be that far away. This tsunami
could strike in our lifetime.
Even though it seems so
extraordinary when we consider
it in human terms, and we talk
about a tsunami striking the
east coast of North America and
causing huge devastation on the
scale of the Sumatra tsunami--
but this is what happens in the
geological record, this is what
Earth does.
>> Although tsunamis have been
documented for thousands of
years, it is only in the last
century that geologists have
been able to prove how they are
connected to the movements of
the Earth.
By analyzing data from the great
Chilean earthquake of 1960,
scientists were finally able to
firmly link earthquakes with
tsunamis. Unearthing buried
Native American settlements
proved that the Cascadia
fault line in the Pacific
Northwest was an active tsunami
threat. Corals in the Indian
Ocean proved that some
earthquake-generated tsunamis
follow a pattern, and strike the
same area with regular
intervals. And the giant rift in
La Palma's landscape shows that
tsunamis generated by landslides
are also a very real threat,
megatsunamis, which could prove
to be the biggest waves that
threaten our coastline.
Tsunamis are an inevitable part
of Earth's dynamic structure.
Their capacity to destroy is
awesome, but, as scientists
begin to understand more about
the origins of tsunamis, they
are coming closer to predicting
where and when these monsters
may strike.
== sync, corrected by elderman ==