>> Earth, a unique planet,
restless and dynamic.
Continents shift and clash,
volcanoes erupt,
glaciers grow and recede--
titanic forces that are
constantly at work,
leaving a trail of geological
mysteries behind.
This episode investigates
the deadliest and most
destructive volcanic event
in U.S. history.
Mount St. Helen's,
a pristine snow-capped mountain,
suddenly blew 600 feet
off her summit in a type
of eruption no one had ever
witnessed before.
Scientists trying to understand
what made this event so lethal
uncover evidence for one
of the biggest landslides
in history, a sideways-directed
blast that knocked over
230 square miles of forest
and mega mud flows that
thundered down the valleys
and destroyed everything
in their path.
What scientists have discovered
from this unique event brings
geologists one step closer
to understanding
"How the Earth Was Made." S02x10 Mt. St. Helens Original Air Date on February 2, 2010
-- Sync, corrected by elderman -- -- for addic7ed.com ---
In Washington State,
100 miles south of Seattle,
stands Mount St. Helen's,
one of 20 major volcanoes
that form part of the Cascade
Mountain Range at the
North American West Coast.
Before May 18, 1980,
she was at the center
of a thriving recreational
paradise and prosperous
timber industry.
>> The volcano had
a beautiful conical form.
It was called the Mount Fuji
of North America,
and the form was a bit concave.
>> But beneath her beauty
lay an ominous secret.
The mountain was brewing
something that had
a deadly potential.
The story began
on March 20, 1980,
when a 4.2-magnitude earthquake
woke Mount St. Helen's
from a slumber that had lasted
123 years.
The last known eruption
was witnessed in 1857
by local tribes.
In 1980, the earthquake
was an alarming sign because
warthquakes may be an indication
that an eruption is building up.
Earthquakes can happen
when magma rises from deep
inside the earth,
shifting and breaking the rock
on its journey up.
>> The very first signals
we had were earthquakes
at shallow depth
neneath the volcano,
and within a matter
of just a few days, it was clear
this was something unusual.
So the word went out to
scientists around the country,
and very quickly we started
to converge at St. Helen's
and started trying to understand
what was going on,
and what we saw was the volcano
was becoming more and more
and more restless.
>> Volcanoes are dangerous
because they are hard
to predict, and in 1980,
the science of predicting
volcanic eruptions was still
in its infancy.
The most recent explosive
eruption that occurred
on the continental U.S.A.
was Lassen Peak in California
in 1915. Since then,
most of the experience
volcanologists had gained
came from studying
quiet lava flows on Hawaii.
>> Volcanoes are incredibly
complicated natural systems,
and they're always full
of surprises.
St. Helen's surprises us
all the time.
Other volcanoes surprise us.
But we're learning.
>> Armed with the latest
scientific equipment,
volcanologists were anxious
to study a possible eruption.
Little did they know that they
were about to witness
the most deadly volcanic blast
in the U.S. in living memory.
On Coldwater Ridge, 6 miles
mortheast of the volcano,
they installed a trailer
with highly sophisticated
equipment and began to closely
monitor the mountain.
From there, they had a perfect
view over the volcano.
>> We had a front-row seat
to seeing the evolution
and reawakening of a major
Cascade volcano, and we were
fortunate in that we had people
here with a lot of energy.
People were working
15 to 20 hours a day.
>> In addition to earthquakes,
another key indicator
for volcanic activity
is gas emissions.
Magma made out of hot molten
rock contains gases that come
from deep inside the earth,
30 miles down.
As magma moves up from these
depths, there is less rock
weighing down on it from above,
so the pressure on the magma
decreases. Gases dissolved
in the magma escape and rise
to the surface.
But gases are not just
a telltale sign of rising magma.
They are also responsible
for the explosiveness
of the eruption.
The greater the buildup of gas
pressure within the volcano,
the more explosive
yhe eruption will be.
>> Well, this is a simple
experiment to demonstrate
the importance of gas pressure
in a magma.
The bottle is partially filled.
This is filled about 80%
with water. This will be
simulating a volcanic eruption.
So I'm going to carefully
place the bottle here.
We'll tilt it a little bit
away from me.
I'm going to put on
my safety goggles.
And now I'm about ready
to start pumping.
Here we go.
Oops. There's a little bit
of gas coming at the bottom.
A little bit more.
And the pressures are up to
about 60 pounds per square inch.
Whoa!
Did we get it?
We got it! Yay!
>> Like in the bottle,
the presence of gas
at the surface of a volcano
is a sure sign that an explosive
eruption is building.
In spring 1980, Casadevall's job
was to detect these gas
emissions. The gas he was
looking for was sulfur dioxide.
It's a gas that smells like
rotten eggs and is associated
with volcanic activity.
But the key to the measurements
wasn't the smell. The secret
was subtle differences
in the color of the light.
>> This instrument looks
at the light in the sky,
and it looks for the presence
of certain molecules,
like sulfur dioxide, which also
absorb light from the sky.
And it measures the difference
between the light absorbed
by sulfur dioxide and the light
available in the rest
of the sky.
>> In March and April 1980,
Casadevall and his team
were using this instrument
to detect the amount
of escaping gases.
They assumed that the gas levels
would increase prior
to the eruption as more
and more magma would rise
inside the volcano.
But in 1980, the assumption
proved wrong.
Gas emissions didn't change,
even though earthquakes
were getting stronger,
and hundreds of small tremors
were recorded.
>> There was really
no significant variation.
It was a very low level
of sulfur dioxide emissions.
And there was nothing in those
emission rates that really
indicated that an eruption
was just around the corner.
>> But by late April,
after 5 weeks of tremors,
the mountain gave them
another clue to what
was brewing inside.
On the north face, a huge bulge
was growing outwards.
>> A casual observer would look
at the volcano and say,
"well, it's not longer
a nice fuji-type shape."
But in fact, the north side now
is bulged out, and it was
obviously deformed in some way.
And we were trying to understand
what could have been causing
that deformation.
>> It was the first time
scientists were able to monitor
the deformation of a mountain.
On Coldwater Ridge,
they installed an instrument
that uses laser technology
to get precise measurements
as to how fast the bulge
was growing.
>> What we were trying to do
was to focus a laser beam
from this instrument
on a reflector in the volcano,
receive the returned
reflected signal, and then
measure that distance.
>> The reflectors they used
were small mirrors
about 3 inches across
they had fixed on the bulge.
>> As was the case in 1980
before May 18th,
the north flank of the volcano
was moving outward.
It was bulging outward.
And so the distance
was getting shorter.
And what we learned is that
from Coldwater 2, that distance
was getting shorter
about 5 feet a day.
>> By May 11th, the bulge
had expanded outward
a staggering 450 feet.
Dzurisin had a hunch
that it was caused
by rising magma.
We knew that the north flank
was deforming. We knew
that something had to be
causing it to deform.
What could that be?
Well, it could be magma forcing
its way up into the volcano,
shoving the north flank aside.
That was a possibility.
Well, what else could be
causing it? Well, maybe
the earthquakes were simply
causing the volcano to become
unstable as a result of gravity.
Maybe there was just
a slow landslide going on.
It was very difficult
to understand or to make
a measurement that would
tell you the difference.
The plausible story was
that magma was forcing its way
up under the volcano.
>> As the bulge grew,
the flank of the mountain
became increasingly unstable.
Still, scientists had no idea
how deadly the eruption
would turn out to be.
>> So we didn't know for sure
until... until it happened.
But as the bulge continued
to grow, we knew we were getting
closer to the final outcome.
We just didn't know
what that would be.
>> There were other signs
that an eruption was imminent.
Earthquakes became more frequent
and stronger as time went on.
Authorities feared the worst
and zoned off the area
around the volcano with limited
access for the public.
In spring 1980, geologists
were dealing with a number
of clues that Mount St. Helen's
was building to an eruption.
Earthquakes were an indication
that the volcano was waking up.
Despite low and unchanging
gas emissions, a growing bulge
on the north face suggested
that the magma was indeed
on the rise.
Mysteriously, after May 14th,
the volcano quieted down.
There was hardly any seismic
activity, and the bulge grew
at a slower rate.
On May 17th, officials gave in
to pressure and allowed some
people with property inside
the restricted area to gather up
whatever they could.
Another group was scheduled
to enter for 10 am
the next morning.
But on that day,
disaster struck.
>> On the morning of May 18th,
scientists were about to witness
one of the worst volcanic
disasters in modern history.
For more than 2 months,
a team of volcanologists
had been monitoring
Mount St. Helen's.
>> That's another reason
why May 18 was a surprise,
Because basically in all of this
data we collected before,
there wasn't anything that told
that, you know, May 18th
was going to be the day.
>> David Johnston, a young
volcanologist with the U.S.
Geological survey, was on duty
that day. He had spent the night
on Coldwater Ridge to carry out
measurements of the growing
bulge.
>> It's interesting that even
on the morning of May 18th,
the measurements that Dave made
indicated that that bulge
was still growing at about
the same rate.
>> The same morning, Dan Miller
was on his way to Cowater
Ridge to check on
the time-lapse camera they used
for filming the north face.
>> I was headed to the north
on interstate 5 out of
Vancouver, Washington,
and as I got a few miles
north of town, there's
an overlook point as you go
down the highway where you can
look off to the east
and see Mount St. Helen's,
and I looked over there, and it
was a beautiful clear day,
and there was Mount St. Helen's
with this giant mushroom cloud
going up above it.
At that point, I knew something
very serious was underway.
>> From a safe distance,
35 miles away, Miller witnessed
how the eruption unfolded.
>> The first thing I did
was went to our radio,
our communications radio,
and I made some calls up to Dave
to try to raise him and find out
what was happening.
And not only did I not reach
Dave, but even our repeater,
which was on a mwuntain peak
that was another few miles
to the north of Coldwater 2,
did not answer, indicating
that it had been destroyed.
And that was very scary.
At that point, I realized
that something bad had probably
happened to Dave.
>> Thick dark smoke was
billowing out of the crater,
obscuring the view.
Within hours, daylight
turned murky grey and reduced
visibility up to 300 miles
northeast.
It wasn't until 24 hours later
that the air was clear enough
for scientists to inspect
the devastation.
>> The entire landscape
was almost unrecognizable
to those of us who had spent
almost 2 months before
the big explosion on May 18
working up there every day.
>> Suddenly I realized
that there was complete
and utter silence.
There were no insects.
There were no small animals.
And there were no colors.
The only color was ash grey
for as far as I could see.
>> We made our way up along
the edge of the ridge,
and we found the small quarry
where Dave's trailer
and our vehicle had been parked
on the morning of May 18th,
and we could see
that it was gone.
>> Neither Johnston
nor the trailer were ever found.
A total of 57 people were killed
along with thousands of deer,
elk, bears, and other wildlife.
230 square miles of forests
were destroyed, and the eruption
had torn a 2,000-foot-wide
crater in the summit.
>> It was no longer
a beautiful fuji-type volcano.
And in fact, we could see
that the top of the volcano
appeared to be missing
or was obscured.
>> In the months to come,
scientists faced the difficult
task of finding out
what exactly happened
on that fateful day.
They searched the ground
for clues and methodically
pieced together the chain
of events that had led
to the devastation.
The first important clue
was an earthquake measuring 5.2
that shook Mount St. Helen's
at 8:32 that morning.
The second piece of evidence
came from photographs taken
by tourists who flew over
the mountain around
the same time.
>> They looked down, and they
were able to document,
by a series of photographs,
some shaking on the top
of the mountain,
and then right afterwards,
the whole front of that mountain
started to move sideways.
>> In a series of still
photographs, they documented
how the bulge collapsed.
>> A magnitude-5.1 earthquake
caused the north flank,
which was greatly weakened
by the deformation,
to break loose in the form
of a giant landslide.
>> The volcano just couldn't
take it anymore, and the north
flank became unstable
and slid away.
>> Within seconds,
1,300 feet of the mountain
slid down and destroyed
everything in its path.
What used to be a quiet
mountain valley with the Toutle
River running through it
was now filled with debris
up to 600 feet high,
forming a hilly terrain
known as the hummocks.
From the amount of debris
from the landslide,
scientists calculated
that 2/3 of a cubic mile
of rock slid down the mountain,
enough to bury Washington, D.C.
under 50 feet of rubble.
It was one of the biggest
landslides ever recorded
in history.
It tore a gaping hole
in the side of the mountain
almost 2 miles wide
and over 2,000 feet deep.
To scientists, it was a mystery
why suddenly the entire northern
flank of the volcano collapsed.
Geologists today can still
follow the trail of destruction.
>> What we're looking at here
is a part of a large debris
avalanche. We're looking at
one of the hummocks.
And this is a rock outcrop
that's actually outcropping
in the hummocks,
and the coloration that you see,
first of all is telling you
that this has been altered.
>> This color provides
an important clue
to why the landslide
became so big.
Instead of the usual black
of volcanic lava rock,
it is yellow.
This is a sign that the rock
came in touch with hot water,
turning some of the minerals
in the rock yellow.
Geologists found the same
yellow rock in the crater wall,
suggesting the discoloration
must have happened
on the mountain
before the eruption.
>> So you have rainwater
or glacial water that seeps
down into the mountain,
gets close to the magma,
heats back up, and as it comes
out of the mountain,
then it starts to change
and chemically alter these rocks
and turning them, you know,
into these different colors.
>> But the hot water
didn't just change the color.
More importantly, it also
weakened the rock.
>> So you can see how crumbly
these rocks are just by kind of
digging your hammer through
here, and the reason
they're so crumbly is because
when the hot water moves through
and alters them, they sometimes
altered the clay and some really
soft materials. So if you took
any other rock, it would be
much stronger.
>> This yellow crumbly rock
isn't just found here,
but stretches over 17 miles
throughout the valley,
suggesting that large parts
of the mountain were rotten,
weakened before the eruption.
>> So probably what had been
happening over thousands
of years is magma
down on the volcano
heating up water,
and this acidic water
was gradually rotting out
the center of the volcano.
It couldn't be seen
anywhere at the surface.
>> When the bulge on the north
side finally collapsed,
it pulled along big parts
of the rotten volcano
and left behind
the horseshoe-shaped crater
St. Helen's is famous for today.
>> This volcano is just
a sand pile, if you will.
It had very little internal
integrity or strength,
so that when failure did occur,
literally part of the mountain
slid away.
>> But more destruction
was to come.
Within minutes of the landslide,
Mount St. Helen's channeled
her fury into another
deadly force.
>> The air turned absolutely
black, so nobody could see
anything, but a few of these
witnesses that managed
to survive out in the very edge,
the ground shook intensely,
and they sensed that all
the trees were coming down
at once, even though
they couldn't see it.
>> The landslide had spread
east and west, but this force
surged in a northerly direction.
Within 3 or 4 minutes,
it destroyed everything
on Coldwater Ridge
and ripped out trees
in a 230-square-mile
fan-shaped area.
>> Ao even where we're sitting
here, 8 miles from the volcano,
tou can see this ridge
behind me. This ridge
is 3,000 feet tall,
and all the texture
that you see on this ridge
are the trees, the old-growth
forest trees that were blown
down by the surge that went up
and over this thing
like it wasn't even there.
And so for the surge to have
gone up and over this,
it had to still have been going
roughly 300 miles per hour,
and then it continued
9 miles farther than that
before it finally stopped.
>> To geologists,
this was a surprise.
They had never witnessed
a sideways eruption before.
>> Scientists were intrigued
as to what had caused
this devastating surge.
So they began searching
the ground for evidence.
5 miles northeast of the crater,
Waitt is revisiting
the old deposits.
Mixed with burned wood
from the shredded trees,
he also finds rock.
To the untrained eye, there is
nothing unusual about it,
but not so for the experts.
>> It's clearly young rock.
It's relatively light,
and there's lots
of little voids in here.
In other words, little bubbles
that are frozen in the rock.
So this was the rock that was
growing--there was a hot liquid,
almost solid liquid, that was
growing inside Mount St. Helen's
and causing the bulge
before May 18th.
>> This small rock was
a crucial piece of evidence for
scientists trying to figure out
the chain of events.
After the landslide
tore a gaping hole into
the north flank of the mountain,
it exposed the magma underneath.
Without a cap of earth
to keep it sealed,
the magma suddenly expanded
and surged outwards,
pulling along rock
from inside the mountain.
>> You can envision it
as sort of a colossal-sized
ash hurricane. It was a cloud
of rocks and ash and hot gases
that was maybe several thousand
feet thick that was moving
across the countryside at speeds
of several hundred miles
an hour, a very turbulent
mixture with blocks as large
as 3 or 4 feet in diameter
flying through the air.
It was incredibly destructive.
>> After the initial surge,
Mount St. Helen's turned quiet.
For half an hour, there was
calm and tranquility.
Then the volcano began
hurling its fury skywards.
[explosions]
An enormous mushroom cloud
formed high above the volcano,
3 times as tall
as Mount Everest.
Ferocious explosions
went on for hours, releasing
huge amounts of energy
equal to 27,000 Hiroshima-sized
atomic bombs.
What happened on May 18, 1980,
became a landmark event
for scientists.
It provided them with
an unprecedented chance
to study a lateral eruption.
Discolored rock in the valley
and in the crater wall
were evidence that the mountain
was rotten before the eruption.
Grey volcanic rock
9 miles north of the volcano
was evidence that the landslide
uncorked a massive
lateral blast.
At 5:30 in the evening,
the volcano began to slow down
until it finally quit.
But there was more impending
danger, as the eruption
had caused another
cataclysmic effect.
>> On May 18, 1980,
Mount St. Helen's exploded
in a type of eruption
never witnessed before.
one of the largest landslides
in history triggered a powerful
sideways-directed blast.
Ferocious explosions followed
and formed an immense
mushroom cloud.
Late that afternoon,
the volcano slowed, but more
chaos was about to strike,
as the eruption had triggered
another destructive process.
Hot volcanic ash had melted
the snowfields on top
of Mount St. Helen's.
Hundreds of tons of meltwater
mixed with soil and formed
a series of mud flows
that cascaded down the slopes.
>> Most people don't realize
that this hazard can affect
people living so far downstream
because up to 100 miles
from a volcano can still be
a hazard zone for these kind
of volcanic mud flows.
>> The biggest of the mud flows
came down the Toutle River
Valley. On its way there,
it reached record speeds
of 90 miles per hour
and raced over hills
as high as 20-story buildings.
It destroyed a total
of 27 bridges, nearly 200 homes,
and more than 185 miles
of highway and roads.
Today, its remains are still
preserved on the banks
of the Toutle River.
>> This deposit is an excellent
example of what we scientists
call a lahar, but other people
refer to as a mud flow--
A big massive flow of material
that's much like wet concrete
that was coming down the river
as a huge wall of material,
pushing logs and debris
in front of it.
>> At first, it was a mystery
how this mud flow had become
so big, but the rocks
provided a clue.
>> What we see are rocks of
different types that have come
down from Mount St. Helen's.
Some of these are actually
from the original cone
of the volcano that collapsed
as the debris avalanche.
>> Geologists could now
piece together what caused
these destructive mud flows.
These rocks from high up
in the volcano came from
the landslide that had been
thrown in the valley
in the first minutes
of the eruption.
When meltwater mixed with
the landslide debris,
it formed a gigantic mud flow.
This incredible torrent
lasted till late that night
and dumped more than 65 cubic
miles of mud along the way.
Even 30 years later,
proof of its destructive power
is still in the field.
>> These lahars came down
and totally buried this forest.
We see these standing stumps
of trees that are the remains
of what is often referred to
as a ghost forest.
This was buried by this lahar.
The trees were killed,
and we only see them now because
of the erosion of the river
which has come back in
and eroded into the bank
and uncovered them.
So this is a fantastic clue
of the power and the destruction
of this lahar, which completely
inundated this lower valley.
>> But one deposit farther
upstream was causing confusion
in the investigation.
It looked like a lahar deposit,
but instead of volcanic rock,
it was full of rounded
river pebbles.
>> The scientist who first
studied this wasn't sure
this was a lahar deposit
because it contained so much
of this rounded river rock,
which is characteristic
of streambed deposits
and not lahars.
But then he realized
that it has this very, very hard
compact matrix in it and it was
not bedded or layered in any way
and came to the conclusion
this had to be a huge lahar
that was probably something
on the order of the flow
of the Amazon River.
>> Scientists were stumped.
Not only did this deposit
have rounded river rock,
it was also much bigger than
the deposit from the mud flow
that tore through the valley
on May 18th.
If it wasn't part
of the 1980 lahar,
where did it come from?
Geologists decided
to investigate further and took
samples back to the lab.
Radio-carbon dating showed
that this deposit swept
down the valley 3,000 years ago.
>> If we had been standing on
this spot about 3,000 years ago,
we would have first heard
a very low rumble that would
have gotten louder and louder.
And if we hadn't heeded
that warning, we would have seen
a huge wall of broken trees
and debris coming around
the river bend, probably
at 30 or 40 miles an hour
that would have been
hundreds of feet high.
And that wall of debris
and mud and rock would have
then just swept through here
like a huge freight train,
literally wiping the valley
clean of anything in its path.
>> But where did this ancient
monster flood come from?
The only place that could have
stored that amount of water
and rounded rock was Spirit Lake
35 miles upstream.
This discovery was crucial
because there was
an impending danger that nature
would repeat itself.
Not only did the landslide
that initiated the 1980 eruption
flow west into the Toutle
Valley, it also went east
into Spirit Lake and blocked
its exit. As rivers
and meltwater kept flowing in,
water rose to dangerous levels.
>> It became a very big
wake-up call for the hazards
community, because if this sort
of flood and lahar had happened
in the past, it could happen
again, and the 1980 deposits
dammed Spirit Lake once again
with the same type of weak,
unstable dam that had existed
in the past.
>> Authorities had to act
quickly. Within a couple
of years, Spirit Lake would
have filled up again, and had it
been allowed to overtop,
it would have caused
a catastrophic flood just like
the one 3,000 years ago.
>> The Corps of Engineers
came in. They immediately
devised a plan which involved
pumping water out of the lake
to keep the lake level stable
for the short term.
Their long-term solution
was to drill a boring
through a mountain ridge,
creating a permanent drain
so that Spirit Lake could never
get above that height,
and the danger for
an overtopping flood
was then eliminated.
>> Scientists now understood
what happened on May 18th.
Volcanic rock in mud deposits
along the banks of the Toutle
River valley is evidence that
gigantic mud flows thundered
down Mount St. Helen's,
and rounded river pebbles
in a 3,000-year-old mud deposit
became a warning sign
that Spirit Lake was able
to spill over and cause
an even bigger lahar.
In the summer of 1980,
scientists thought the May
eruption was their chance
of a lifetime, because
major volcanic eruptions
in the Cascades happen only once
or twice every hundred years.
But they were soon to be
proven wrong. After 2 decades
of inactivity, the mountain
began to stir again.
>> The explosion of Mount
St. Helen's in May 1980
scarred the mountain
with a massive crater
on its north side,
but in the summer
after the eruption, the volcano
began to rebuild itself.
Thick magma slowly rose
to the surface and formed
a dome inside the crater.
Had the activities continued
at the same rate, it would have
taken about 200 years
to rebuild the mountain
to its pre-1980 size.
But in 1986, magma flows ceased,
and the volcano died down.
Life returned to normal and
adapted to the new landscape.
Plants and trees took hold
in the fertile volcanic soil.
Elk and other animals
migrated back to the mountain.
Then on September 23, 2004,
the ominous rumbling began again
and put volcanologists
on alert.
>> The entire Cascade range
in the western U.S.
produces on average
about 2 eruptions every century.
So you think, well,
that's one eruption per career.
and St. Helen's in the 1980's
qas ours, and we all assumed
that that was it.
But we got a second chance.
>> Mount St. Helen's
qas cooking up another mystery.
Small earthquakes became
stronger and more frequent.
GPS measurements detected that
the area around the mountain
was sinking.
>> There was one continuously
recording GPS instrument
around the volcano,
and it's code name was JRO-1.
JRO-1 had not moved
in any unusual way
right up until the day
the earthquakes started.
And then on that very day,
it started to move.
It moved toward the volcano
and downward, as if that entire
area of the crust was sagging
down toward the volcano.
>> The only plausible
explanation for the sinking land
was that the magma reservoir
deep underground was shrinking.
In earlier surveys, scientists
had detected a vast pool
of molten rock 8 miles
under the volcano.
If it was getting smaller,
magma had to be on its way up
towards the throat
of the volcano.
The renewed activities
caused widespread concern.
Scientists feared another
eruption was building up.
And they were puzzled what kind
of eruption it would be.
In search of an answer,
scientists turned to St. Helen's
early days.
>> Volcanoes are all
very individual. They have
individual types of eruptions
and traits, and what they've
done in the past is what they're
going to do in the future.
>> The key to past eruptions
is ancient volcanic rock.
Mike Clynne has specialized
in mapping these old deposits.
Southwest of St. Helen's,
he investigates an area covered
with large dark boulders.
A close look reveals the type
of eruption they formed in.
>> We know that this rock
came from a lava flow
because it has big crystals
set in a much finer grained
ground mass of little crystals.
The big crystals grew
in the magma chamber
while the magma was deep
under the volcano.
And the fine-grained ground
mass, which is tiny crystals,
grew when the lava erupted
at the surface and froze.
>> Radio-carbon dating
established the rock was born
2,500 years ago.
The nature of the eruption
it formed in was slow and quiet.
>> This kind of lava flow
erupts from the mountain
as a liquid, and it flows down
the mountainside under gravity.
As it flows away
from the mountain, it cools
until it becomes so viscous
that it can't flow anymore.
So that's where it stops,
and that's what you see here,
is the end result of emplacement
of this kind of lava flow.
So they're not dangerous.
You can stand and watch it
come down at you.
From deposits like these,
scientists could tell
that Mount St. Helen's
had produced a number
of quiet lava outpourings
in the last 300,000 years.
They slowly built up
the mountain from a small
cluster of rock
to a conical-shaped volcano.
But northeast of the mountain,
Clynne finds a different deposit
which tells a story
of a much more dangerous episode
in St. Helen's past.
>> We look at this deposit,
and there's a couple
of characteristics
that are important.
First of all,
that it's very loose,
and that it's composed
of rock fragments that are
all about the same size.
Another important characteristic
is that the rock fragments
are touching each other.
There's no material
in between them.
Well, that tells us
that these rock fragments
came here by falling
out of the air.
It's a big explosive eruption
that sends the material
very high into the sky,
and when the wind dies down,
they start to fall,
and they pile up here.
>> The rock fragments are
very light pumice that formed
during a violent eruption
similar to the one that produced
the huge mushroom cloud
in May 1980. But age-dating
revealed that this deposit
was much older.
This event happened
3,500 years ago, and compared
to the 1980 eruption,
scientists found evidence
that it was much more dangerous
and spewed out 4 times more
rock and ash.
>> This is the biggest eruption
in Mount St. Helen's history,
and it was about a cubic mile
of material that was erupted
at this time. And we know that
because we trace out
the deposit, measure
its thickness and its distance,
and you add that all up
together, and you get
the volume of the eruption.
This deposit can be traced
all the way to central Canada.
>> Studying Mount St. Helen's
past has revealed
that she has an unpredictable
eruptive nature.
>> Mount St. Helen's had
everything from relatively
benign lava flows to quite
violent eruptions in the past.
So it's very hard,
when a volcano starts acting up,
to know which of these
possibilities is going
to happen, and of course,
the various scientists,
we discuss and argue
and all that kind of stuff
what we think is going on,
and nobody truly knows
what's going on.
>> Scientists investigating
Mount St. Helen's have found
clues that show different
eruptive behaviors in her past.
Large dark boulders are evidence
that she is able to produce
slow and quiet eruptions.
A thick deposit of white pumice
is evidence for an ancient
dangerous eruption 4 times
larger than the one in 1980.
Fortunately, the events that
began in 2004 took a lucky turn.
The magma did reach the surface,
but it had lost
its explosive power.
It flowed out like toothpaste,
in a dome-building style
of eruption. As geologists
carried on studying
Mount St. Helen's,
a volcano 4,000 miles away
began to stir. Because of
their experience in 1980,
scientists were convinced
a major catastrophe was
about to unfold, and this time,
12,000 lives were at risk.
>> The eruption of Mount
St. Helen's in May 1980
took scientists by surprise.
It was the first time
they witnessed the failure
of a massive bulge,
a huge landslide,
and a powerful lateral blast.
>> Prior to 1980, we just
didn't have the knowledge
to make those kinds
of specific predictions.
We started learning
in the 1980's at St. Helen's.
We've continued to learn
at volcanoes around the world,
and we've had some successes.
>> Forecasting volcanic
eruptions is difficult because
there is no strict pattern
to the buildup.
But as scientists are getting
more experienced in observing
volcanic behavior,
they are getting better
at their predictions.
In 1995, Soufriere Hills volcano
on the Caribbean Island
of Montserrat became restless.
It had been quiet for 350 years
until earthquakes rumbled it
to life again.
Residents were used to
a gently steaming mountain
and simply hoped
it would die down, but when
the earthquakes got stronger,
officials called for help.
A team of U.S. Volcanologists
Flew to the Caribbean
to monitor the reawakening.
>> There developed a situation
there whereby there was a region
of high seismicity occurred
just as St. Helen's.
If you went up on the mountain,
as we did, they just about
knocked you to your knees.
They were very strong events.
>> Strong earthquakes weren't
the only warning signs.
On the south side
of the mountain, they observed
how a monstrous bulge
began to form.
>> There were cracks
that were occurring.
You could see the cracks
were moving every day.
It looked like the whole side
could fall apart, so we could
get a slope collapse there,
a major slope collapse.
>> By October 1997, the bulge
was growing at a staggering rate
of 280 cubic feet per second.
Scientists were alarmed.
Because of their experience
on Mount St. Helen's,
they knew that a collapse
of the bulge was imminent.
People living in the proximities
of the volcano were in danger.
So they advised the authorities
to evacuate immediately.
>> 8,000 people had to leave
the island. Over 4,000 were
forced to move to a safer
location to the north.
On the 26th of December, 1997,
the volcano struck.
After an intense swarm
of earthquakes, a huge part
of the bulge broke loose
and roared down the valley.
Like at Mount St. Helen's,
the sudden removal of rock
released the pressure
on the magma below.
A lateral blast surged south
and spawned a vertical
ash column 36,000 feet high.
Within 15 minutes, the eruption
destroyed 4 square miles
of the island and completely
buried the island's capital,
Plymouth, under 39 feet of mud.
>> Montserrat is a prime example
where lessons learned
from a big catastrophe
have prevented another one.
>> Almost everything that
occurred at St. Helen's
did occur at Montserrat.
It replicated St. Helen's
not only in the lateral blast
and so forth, but it did
everything that St. Helen's did
on a smaller scale.
>> Scientists studying the
eruption of Mount St. Helen's
on May 18, 1980, have uncovered
a sequence of events
they had never seen before.
A growing bulge on the north
flank of the mountain
was an alarming sign that a pool
of magma was building up
within the volcano.
Grey volcanic rock
from the bulge 5 miles away
was evidence for a powerful
sideways eruption.
A 3,000-year-old mud deposit
became a warning sign that
the valleys around the mountain
have been repeatedly swamped
by huge mud flows.
A deposit of white pumice rock
found all the way up to Canada
showed that Mount St. Helen's
is able to produce eruptions
4 times larger than the one
in 1980.
As the investigation has shown,
Mount St. Helen's is full
of surprises.
>> St. Helen's, I think of it
as a teenager among the Cascade
volcanoes. It's young,
it's vigorously active,
it's explosive,
it's very energetic.
Even though to our eye,
as we look at it,
it appears to be sleeping,
it's active. It's doing
what it's been doing
for tens of thousands of years.
>> Mount s helen's looks
set to continue her erratic
and at times violent outbursts.
Her deadly potential
is a stark reminder
the earth is never at rest.
-- Sync, corrected by elderman -- -- for addic7ed.com ---