All language subtitles for Killer Landslides PBS NOVA 2014 720p HDTV EN Sub

NARRATOR:
A sudden landslide.

Nobody anticipated
that it would cut loose

and bury that entire village.

NARRATOR:
Some victims are buried alive.

Others narrowly escape.

ROBIN YOUNGBLOOD:
I saw a gigantic wall of mud,

and then we were hit.

Houses were exploding.

911 CALLER:
Oh my gosh!

911 OPERATOR:
Are there any injuries?

911 CALLER:
Yes, there are people
yelling for help!

NARRATOR:
A whole community is cut off.

What's going on
with the highway?

I'm hearing rumors
that there's a mudslide.

NARRATOR:
A neighborhood, wiped
from the face of the earth,

is invisible to rescuers.

BILL QUISTORF:
All I could see was

just a vast wasteland.

There were no homes.

There were no remnants of homes.

NARRATOR:
Volunteers risk their lives

to extract the missing
from the mud.

DAYN BRUNNER:
It was so eerie.

We could hear moaning.

We walked past four bodies.

YOUNGBLOOD:
He was just drenched

and shivering and shaking.

NARRATOR:
What could have triggered
the tragedy?

ERNIE ZELLERS:
Where's the baby?

I thought I was losing him,

and I'd say,
"Stay with me, Bud!"

NARRATOR:
Can science explain

how earth can turn to liquid
in an instant?

Everybody feeling ready
for go time here?

GEOLOGIST:
Okay, we're ready for water.

Here it goes!

DAVID MONTGOMERY:
Something like 22 inches
of rainfall.

You know, that's almost
two feet of rain in a month.

NARRATOR:
Some of these disasters
are triggered by rain,

but not all.

Around the world,

scientists fear that landslides
could be on the rise.

Now, geologists are hoping
to spot the next big one

before it strikes,
to warn those in its path

and avert further loss of life.

There's no word for it
other than "tragedy."

NARRATOR:
How far out can we predict
landslides?

The closer you get to an event,
the easier it gets to predict.

It will be a very big one!

A huge one!

NARRATOR:
The race is on
to sound the alarm

and save lives
from "Killer Landslides,"

right now on NOVA.

Major funding for NOVA
is provided by the following:

We're committed to strong.ng.

And the Corporation
for Public Broadcasting

and by PBS viewers like you.

Additional funding for "Killer
Landslides" is provided by:

Furthering the values that
contribute to a healthy planet.

Millicent Bell, through:

And:

NARRATOR:
Late March.

Record-breaking rains
have hit western Washington.

10:30 a.m.

Families are enjoying the first
sunny weekend of spring.

It's been raining for months.

In an instant, this idyllic
morning becomes a nightmare.

The saturated earth on a slope
nearby starts to slip.

(rumbling)

A landslide comes plummeting
across the valley

towards the unsuspecting
families.

(rumbling and crashing)

AMANDA SKORJANC:
The sound is like this horrible,
rumbling, wet....

(rumbling)

I turned and I held Duke,
and I did not let him go.

NARRATOR:
Sitting at her table
with a friend,

Reverend Robin Youngblood
has no time to escape.

We heard this horrible sound.

It sounded like a 747 was going
to crash in the valley.

NARRATOR:
Half a mile away
from Robin's home,

Amanda Skorjanc
is in the kitchen

with her five-month-old baby,
Duke.

SKORJANC:
The sound is unexplainable,

and I will never get it
out of my head.

YOUNGBLOOD:
We ran to the window
when we heard that sound,

and I looked to my right

and I saw a gigantic
wall of mud,

and then we were hit.

SKORJANC:
And it was like a movie.

Houses were exploding,
and the next thing I remember is

our neighbor's chimney
coming into our front door.

RICHARD IVERSON:
Everything that was in its path,
essentially, it picked up

and was throwing in front of it:
trees, debris from houses.

It would be like being hit

with 1,000 battering rams
at once.

It was just a completely
unsurvivable sort of event.

YOUNGBLOOD:
We were slammed,
and we were underwater in mud.

The house was racing
across the valley.

And then we stopped.

NARRATOR:
Without warning, this hillside
turned to liquid mud,

wiping out 49 homes.

The hillside collapsed,
but it didn't stop there.

It dammed the river
and continued on

to rampage
through a neighborhood,

reached highway 530,
and kept going.

All is now a wasteland
of mud and debris,

one square mile buried
under 15 to 75 feet of mud.

911 OPERATOR:
911, what is your emergency?

FEMALE CALLER:
There's, like, a mudslide,
and everything is gone!

The houses are gone!

There is a house on 530,
and it is covering the road!

I was standing here,

and I heard this noise
and I looked out,

it sounded like a big truck,
and then my lights went out.

MALE CALLER:
My neighbor's house
has been completely taken out

and it's collapsed
on several of them,

and they're trapped.

FEMALE CALLER:
Oh my gosh!

So I walked out the front door,

and then I looked up the road
and then I knew what it was.

I could see the stuff
in the road

and then I knew it was a slide.

Took my phone out of my pocket
and dialed 911.

JUPP (on phone):
There was a big landslide
at the bottom of Skaglund Hill.

NARRATOR:
It's only minutes
after the landslide buries

nearly a mile stretch
of Highway 530.

Everything in its path,
in a tiny community called Oso,

is altered forever.

Rescuers have no idea
if there are any survivors.

JUPP:
It didn't take very long
for the guys to come from Oso.

They were here
within ten minutes.

MIKE BLANKENSHIP:
When you could see dirt

for a mile straight,

you knew you were in
for the long haul.

DAVID MONTGOMERY:
This slide apparently happened

in 138 seconds
from start to finish

in two phases, it seems,

based on the seismic signal
that was recorded

at the seismographic station
at UW.

NARRATOR:
If scientists converted
these seismic waves

to sound waves and sped them up,
this is how they would sound.

(rumbling)

The initial collapse registered
on seismographs 170 miles away.

MONTGOMERY:
Imagining all that material
moving off that valley wall

all the way across the valley
floor in about two minutes?

I mean, that's really hard
to imagine.

PAULO FALCAO:
Oh my gosh.

Look at this!

NARRATOR:
The danger is not over
for the victims or rescuers.

Another part of the hillside
could break free

and come crashing down.

Some landslides strike twice.

Around the world,

landslides occur anywhere
there's elevated terrain,

killing thousands of people
every year.

In just seven months,

222 landslides worldwide
caused loss of life,

resulting in nearly
1,500 deaths.

WOMAN:
Oh my God!

NARRATOR:
They occur in every U.S. state
and cost billions annually.

A landslide is simply
a downhill movement

of earth, rock or debris,

triggered
when gravity overpowers

the binding strength of the
materials that make up a slope.

Some landslides
are slow and shallow.

The top layers of soil or rock
slip over time,

just inches or feet a year.

Others, like mud flows
and rock falls,

move rapidly
and can flow long distances.

Rapid, deep landslides
that travel far,

like the one in Oso,
are the most dangerous

and difficult to predict.

MONTGOMERY:
If you think
about the distinctions

between landslide types,

the sort of deep-seated
landslides

and shallow landslides,

shallow ones usually involve
just the soil

or what we call the regolith,

the weathered stuff
on top of rock.

Shallow landslides
will often involve,

like, a meter
or maybe a couple meters.

The one behind me is
a deep-seated landslide.

The whole valley wall
came down.

NARRATOR:
The raw slope left behind after
a landslide is called a "scarp."

David Montgomery
is a geomorphologist

who studies landforms
and the forces that shape them.

He begins his investigation
at Oso

by surveying it from a distance.

MONTGOMERY:
You can kind of get a sense

for how the old edge
of that plateau

dropped down
as part of the landslide,

but you can also see
at the bottom

how the toe of the slide,
the bottom of it,

spread out laterally
across the valley bottom.

So this solid hillside
started to fail

and then it fluidized,
it turned into a debris flow.

This is a super big landslide
that traveled super fast.

It's really hard to relate
to that in human terms.

NARRATOR:
Even now,
days after the Oso landslide,

chunks continue to calve off.

GEOLOGIST:
That's a big one.

NARRATOR:
This slope has slid
many times before.

GEOLOGIST:
Whoa!

NARRATOR:
To figure out if it could
slide again in the future,

Dave needs to look
into the past.

A technique called Lidar,
laser-based altimetry

that can penetrate
through the tree canopy,

reveals the scars left behind
by past landslides.

MONTGOMERY:
You basically take a laser
and mount it in a plane,

fly it around and shine it down
on topography

and measure the time it takes

for the returns to get back
to the instrument.

So you're basically scanning
the topography

below wherever you have
the instrument.

NARRATOR:
This Lidar image shows
the contours of the Oso Valley

before and then after
the March 22 landslide.

It also shows evidence
of past landslides

up and down the valley.

The yellow landslides
are the oldest,

followed by the tan
and orange ones

which overlap them.

The red slides
are the most recent,

with the crosshatched one

designating
the March 22 event.

It wasn't the biggest landslide
to strike the region.

The large orange landslide

that probably slid
many centuries ago

is nearly twice the size
of Oso's recent slide.

The challenge is to figure out
how long ago

and how frequently
landslides occurred.

That requires sort of
good old-fashioned geology.

You need to go out and try
and find something to date.

NARRATOR:
David Montgomery and his team

found they could readily date
the ancient landslides.

MONTGOMERY:
This is one of the buried logs

that we carbon-dated
at about 5,300 years.

It's buried
in an old landslide deposit.

How do we date it?

Grab a piece of bark,
take it back to the lab.

We got three carbon samples
out of this margin of the slide,

all dated to
about 5,300 years carbon age.

NARRATOR:
Since 1933, aerial photos
and satellite images

have provided even more clues
about the history of the slope.

Pictures show the Oso slope
slid repeatedly,

changing the course of the river
at its base.

The regrowth of vegetation hid
the scars of its unstable past.

MONTGOMERY:
You have this pattern

with this slide on that slope
of essentially failing

and then being quiescent
for a while,

then failing again
a decade or two later.

So this slope was a known actor
in terms of landslides

that happened periodically

involving just the lower part
of the slope

that eventually failed in 2014.

NARRATOR:
Although rescuers in the region
train for landslide disasters,

no one was prepared
for this kind of devastation.

911 OPERATOR:
We have requested a helo
from the Navy

and from our Search and Rescue.

NARRATOR:
The Snohomish County
Helicopter Rescue Team

was the first air support
on the scene.

Check!

NARRATOR:
They use advanced technology

to search for survivors.

Scanning the mudscape

with an augmented reality
mapping system,

pilots toggle between
the mud-gray live video,

which is inset into the green
pre-disaster aerial photography,

showing where the 49 homes
once stood,

where streets were laid out
just an hour earlier.

BILL QUISTORF:
The partner that
I was flying with,

our tactical flight officer,
he told me right off the bat

that there were 30 homes
in the area.

And I said, "30 homes where?"
because all I could see

was just a vast wasteland.

There were no homes.

There were no remnants of homes.

NARRATOR:
A thermal camera
allows them to spot bodies

by the heat they give off.

QUISTORF:
This tool was vital
in helping us search

and determine that there were
no live people in the mud.

NARRATOR:
They expected to find people

near where their homes
once stood,

but the instrument detected
no heat signatures at all.

There was no longer
anything there--

no houses and no people,
dead or alive.

A geologist helped them
to refocus the search.

RICHARD IVERSON:
It took a bit of time
for this to sink in with us

because we were thinking
one way,

whereas the searchers were by
and large thinking another way.

Being trained
as first responders,

they had the mindset that
the place you needed to get to

was the place where
those people had been,

meaning where the houses
had been

before the landslide occurred.

It w immediately clear

that there was going to be
nothing there.

There would be no trace
of civilization whatsoever

back where those houses
originated.

NARRATOR:
When the hill collapsed
with such force,

it pushed all the debris,
houses included,

to the far side of the valley.

It's what scientists call

"the distal end"
of the landslide.

Iverson was able to map out
the direction the landslide,

and anything caught up in it,
would go.

IVERSON:
This was an incredibly
real manifestation

of something
that I'd been studying

on a more abstract level
for decades.

And to see it all play out
right there

and witness firsthand
the damage that it had wreaked,

it was really a very,
very profound experience.

NARRATOR:
The next time
a landslide strikes,

geologists, first on the scene,

could be instrumental
in saving lives.

Robin Youngblood's home

was rafted hundreds of feet
from where it once stood.

YOUNGBLOOD:
I was still conscious.

I couldn't breathe.

My nose, my mouth,
my ears, my eyes,

everything was full of water
and mud.

I knew I had to get out.

I don't know quite how I knew
which way was up.

And I started pushing,
and finally I got air.

RANDY FAY:
Robin and her friend
were the first ones we spotted.

They had gotten on top
of the debris of Robin's home

and were waving
and caught our attention.

The methodology we use for them

involves putting them
in a hammock device.

So they don't have to move
or really participate,

and as long as
we're comfortable

there's no spinal injuries
of any kind,

we can get them out of there
pretty quickly.

ERNIE ZELLERS:
I have her.

Give me some slack!

Are you okay?

YOUNGBLOOD:
They dropped us off and said,

"We're going right back,
we saw somebody."

FAY:
Our crew chief spotted something
moving in the mud.

NARRATOR:
It was four-year-old
Jacob Spillers,

struggling alone in the mud.

He was home with his father
and three siblings,

Brooke, Kaylee and Jovon,

who were watching TV downstairs
while their mother was out.

Jacob was on the second floor.

The landslide carried him
over a quarter of a mile away.

All but Jacob were buried alive.

Jacob at that point was
about waist deep in this

and covered head to toe
with mud,

so it was just kind of
the wriggling around.

So had we not come down lower
and slower to watch that,

well, I don't think we would
have spotted him, frankly.

NARRATOR:
A neighbor miraculously made it
through the mud to Jacob.

But now they're both stuck.

FAY:
It was clear if he was sinking
as a four-year-old,

a big, fat guy like me
was going to have real trouble.

NARRATOR:
Jacob is hypothermic.

His rescuer shields him from
the helicopter's rotor wash.

STEVE KLETT:
We attempted to come down
and put a skid close to a log,

and there just was not enough
rotor clearance

to get down that low.

FAY:
We do a maneuver called
low hover off-loading,

and we do this
in the mountains a lot

if we're working
against ledges

or areas where
we can't land,

and it basically involves
bringing the helicopter down

to a one-foot hover
next to an obstacle,

and then we move on and off
the aircraft

while the pilots
hold it steady there.

I sank probably
a little over ankle-deep

when I stepped off and was
hesitant to move down the slope

for fear I'd get stuck.

So I had a hand line
that I threw him.

And between the two of us,

we were able to pull them up
out of there

and get them up with us.

We handed Jacob
to the crew chief,

and then the other gentleman
turned to leave

and immediately started
sinking again.

So I motioned for him
to come back up,

we put him on board,
and he actually held Jacob

while we flew out of there,

which turned out to be
a good thing

that he was on board with us.

YOUNGBLOOD:
They brought Jacob to us
in the ambulance,

and he was just drenched
and shivering and shaking,

and I mean,
I'm a grandma, right?

So I just told him,

"I'm going to get
those wet clothes off you,

"we're going to put you
in a warm blanket,

"I'll take care of you,

we're going to sing songs,
it's okay."

NARRATOR:
The scope of the devastation
caused by this landslide

is something that even a trained
geologist like David Montgomery

has a hard time accepting.

MONTGOMERY:
Wow.

You know, who would have been
able to imagine that

on the very first nice day
of spring,

the whole mountain
could come down

and run all the way
across the valley bottom?

NARRATOR:
He wants to see for himself
the distal end of the slide,

the place where houses,
people, cars

and the remains of an entire
neighborhood ended up,

bulldozed by the landslide.

Seeing ground zero is a shock.

MONTGOMERY:
What can you say?

It's utter devastation.

We're at the distal end
of the debris flow,

and you can see that

the jumble of wood and soil
that was pushed

as the leading wave
of the debris flow

that ran into the highway
and everything

in between the slide
with unimaginable force

completely torn up
in a chaotic pile of debris.

But notice all the wood
from the trees

that were entrained and pushed
along within the flow

got rafted out to the front.

I've seen deposits
from debris flows before,

but never anything this big
and this extensive.

It's unimaginably large.

The scale of this
is just overwhelming.

NARRATOR:
What's surprising to the experts

is that a 600-foot-high slope
slid for a mile,

many times further than
this slope ever slid before.

It's a central mystery
of the disaster,

something no one expected.

IVERSON:
If the Oso landslide had behaved
in an ordinary fashion,

it might've hit
one or two houses.

That's of course
not what happened at all.

Instead, the landslide mobilized

and very dramatically ran
on the order

of five times further
than you might've expected

based on typical behavior,

and that's what really lead
to all the devastation.

NARRATOR:
David Montgomery gears up

to investigate what's behind
this deadly anomaly.

We are going over to the scarp
of the slide,

which has been actively eroding
since the failure.

And we want to be roped in
and as safe as possible

getting close to the thing.

MAN:
Dave, have you put on
a harness before?

MONTGOMERY:
Uh, I've had them
put on me before.

NARRATOR:
He's roped to four anchors
for safety.

At any moment,

with his weight adding stress
to the top of the landslide,

a chunk with Dave on it
could peel away.

MONTGOMERY:
You can hear the raveling
off the face.

The sediments that are exposed

in the head scarp
of the landslide

are sand and gravel.

It's fairly loose stuff,

and you can hear the individual
particles being dislodged

and rolling down the face
as we stand here.

You can actually see the stuff
coming down.

You can see the plumes of dust
rising up off of the scarp.

NARRATOR:
The loose sand and gravel
can't adhere to the scarp,

so it easily slides
off the slope.

MONTGOMERY:
This is safe enough

that we are roped in.

The head scarp
has been retreating back

since the landslide happened.

It's fairly weak material.

We're obviously hoping that
doesn't happen very soon.

NARRATOR:
What was the top of the slope
before the landslide

is now nearly 300 feet
below the head scarp.

MONTGOMERY:
The area downhill from here
that has all the trees on it

that have been back-rotated
is a big block of the landslide

that dropped out from under
just in front of us

and was essentially
the head of the slide

forming this head scarp.

NARRATOR:
The Oso landslide came down
in two pieces:

the lower half of the slope

that spread out
onto the valley floor

and the heavily treed head scarp

that plummeted
halfway down the slope.

Two events, just minutes apart.

The same thing happened
in Afghanistan

just a few weeks
after the Oso slide

while a wedding took place
in Badakhshan.

(people yelling)

Two slides with long runouts
came crashing down in succession

when rain turned a mountain
to liquid mud.

The first slide crushed homes
in an instant.

(yelling continues)

Eyewitnesses raced
into the deadly mire,

desperately trying to dig out
family members,

when the second slide hit
minutes later,

much larger than the first.

Hundreds, perhaps thousands,

are entombed
in more than 160 feet of mud.

The government declared the site
a mass grave.

(translated):
It's really hard for survivors
to find their homes

using simple tools like shovels.

We haven't recovered
any of the deceased in the mud.

The people are horrified.

They witnessed the tragedy
with their own eyes.

They describe the landslide
as if it were a monster

that devoured their loved ones.

(translated):
My family, including my child
and all my belongings, are gone.

We ask the government
to help us here.

We don't have the necessary
equipment.

(translated):
Some people whose houses
weren't destroyed

still won't return
to their homes.

They'd rather live
in temporary tents

than face the horror and fear
of another landslide.

NARRATOR:
Geologist Haji Mohammad Jamshid

found evidence of cracks
at the top of the mountain,

a known first indicator
of movement on a slope.

JAMSHID (translated):
This shows an opening
in the earth

that is ten meters deep,

and the width is between one

and three and a half meters
wide.

NARRATOR:
With better landslide awareness,

these obvious signs on a slope
above a populated area

can raise red flags in time

for authorities to set up
a monitoring system.

(translated):
It's not possible
for human beings

to prevent natural disasters.

But we can save people

by evacuating them
from landslide-prone areas.

MONTGOMERY:
The unfortunate reality
is that sometimes,

if part of a slope fails,

it can destabilize
the next piece.

Sometimes two happen
in very rapid succession,

like the most recent Oso slide
and like the Afghanistan slide,

and that can be
really heart-breaking

if you have people doing
the very human thing

of rushing to help

and then those people get caught
in the second bit.

There's no word for it
other than "tragedy."

NARRATOR:
Understanding why a landslide
behaves the way it does

is almost like investigating
a crime scene.

Geologists have to search
for clues,

like the composition of the soil
that slid.

Dave Montgomery peels back
the layers of the Oso slope.

It all dates back
to when glaciers were here

15,000 years ago.

MONTGOMERY:
This material is
the glacial lake deposits

that are at the bottom
of the geological pile here.

And it's a mix of silt and clay

that I can just crumble
with my fingers.

NARRATOR:
When wet, the very fine material

that makes up this base layer
of clay

slips like a banana peel.

The layer above it
is a porous, silty sand.

Water drains through it
like beach sand.

MONTGOMERY:
These gray pillars around me
are all made out of glacial till

which came off
of the head scarp.

And the stuff is pretty strong,
it's pretty cohesive,

it holds together well.

It survived the trip down
to here in fairly large chunks.

NARRATOR:
Glacial till is an upper layer
of hard-packed material

left behind by the compressing
action of a glacier

from the last ice age.

It's the layer just beneath

the very loose sand and gravel
at the top.

And we know it's till
because there's boulders,

there's gravel, there's pebbles,
there's sand, and there's clay.

It's everything.

It's like a dog's breakfast
of a deposit.

NARRATOR:
Add to that a regular flow
of groundwater.

MONTGOMERY:
How much of that water
was actually flowing into

and helping to saturate
the material

that failed in the 2014
landslide is an open question.

But there was certainly
groundwater coming in

from the margins of the slide.

NARRATOR:
How much water the layers
on each slope can hold

is a factor landslide geologists
try to measure.

IVERSON:
The contributing factors in the
great majority of landslides

have to do with water.

In the case of this event
at Oso,

there had been prolonged
heavy rain.

The wetter it is,
the more likely it is

that the groundwater pressures
will tend to build.

And it's that increase

that eventually triggers
the landslide.

NARRATOR:
Layers of clay, sand,
glacial till,

and a loose, gravelly top layer

are typical materials found
worldwide on mountain slopes.

This combination of ingredients,
mixed with a wet climate,

paves the way
for a long runout landslide.

MONTGOMERY:
You have the geological setup
of a naturally unstable slope,

and then we get a very,
very wet winter.

The proximal cause
of this landslide is

we had the wettest March
in history,

something like 22 inches
of rainfall in this area.

It's almost two feet of rain
in a month.

BLANKENSHIP:
I live in Washington.

(laughs)

So, it rains a lot
in Washington.

NARRATOR:
The Pacific Northwest
is landslide country.

More rain falls here than any
other part of North America,

as much as 118 inches annually

on the western slope
of the Cascades.

Research suggests climate change
could result in an increase

in the number and intensity
of showers.

This could cause more frequent
landslides on unstable slopes.

But Oso experienced a slide
beyond expectation,

and scientists want to know
what caused the mountain

to turn to liquid so quickly
and flow so far.

Richard Iverson has studied
debris flow for 30 years.

IVERSON:
When we first arrived
on the site

and looked out
across the area of devastation,

it really didn't make sense.

You don't expect a landslide
originating from that height

to travel that kind of distance.

So immediately, that poses

a big question in your mind
scientifically

as to why this thing traveled
as far as it did.

NARRATOR:
The unique physics
of the landslide

was the result of a phenomenon
Iverson knows well,

when the ground turns to liquid
in what's called liquefaction.

Usually when people
hear the word "liquefaction,"

they think of something
that occurs during earthquakes

because when the ground shakes
and you have loose, wet soil,

that soil can liquefy

and buildings can become
destabilized.

But it turns out that landslides
can also cause liquefaction.

NARRATOR:
Iverson's models help illustrate
just how fast

a rapid, deep landslide,
now liquefied, can move.

He believes Oso's
7,600,000 cubic meters of mud

was moving at 60 miles per hour.

IVERSON:
It took less than one minute

for the debris to move
from the source area

all the way across
the flood plain.

That's a distance
of roughly one kilometer.

Here's the scale.

And then for some
extended period afterwards,

it gradually oozes out
along the margins.

NARRATOR:
Virtual Oso
provides some answers,

but what if we could recreate
a real landslide

to learn how far
and fast it'll go?

In Oregon, Richard Iverson
oversees experiments

at the world's largest
landslide flume,

a 310-foot-long concrete chute.

Here, the U.S. Geological Survey

slops together truckloads
of soil materials

to track how they behave
when water is added.

This is how geologists here
study the forces of nature.

They want to figure out
how much rain is too much

on slopes like Oso.

IVERSON:
The experiments are actually
very pertinent

to what happened at Oso.

We put a pile
of loosely packed sediment

in the top of our flume,

and we simply water it
until failure occurs.

The landslide will liquefy

because of the loose
packing configuration

or the high porosity
of that soil.

NARRATOR:
Porosity is a measure
of how much open space there is

between the individual particles
that make up soil.

Loose soil is more porous
than tamped-down earth.

If the soil
were more densely packed,

then it would have much less
inclination to liquefy.

NARRATOR:
Iverson and his colleagues will
measure how long it will take

to turn this solid mass
to liquid.

Everybody feeling ready
for go time here?

GEOLOGIST:
Okay, we're ready for water?

NARRATOR:
Playing Mother Nature,

the team adds rain
to Mount Flume.

IVERSON:
It's very much like
an Oso-type landslide

being triggered by long-term
accumulating rainfall

and building groundwater
pressures.

NARRATOR:
Cracks, showing slippage
at the top of the slope,

soon form in the loose rock
and soil mixture.

The porous slope takes on water
like a sponge.

IVERSON:
Rocks and soil
are an amazing thing

in terms of how they respond
to water.

One slope can take on water
faster than another one can.

NARRATOR:
Instruments relay
7,500 measurements per second.

IVERSON:
We're going to have something
like 70 electronic sensors

deployed in each one
of these experiments,

and some of those
will be measuring

deformation of the slope
internally

as it begins to creep and fail,

and others will be measuring
the water pressure,

some will be measuring
the surface displacement,

so it's really quite a chaos of
cables when we run one of these.

NARRATOR:
This is one instance where
"failure" means "success."

92 minutes after applying
five inches of simulated rain,

the solid slope liquefies.

IVERSON:
We've learned a great deal

from being able to witness these
things hundreds of times over

in our flume.

There's really no substitute
for seeing things firsthand

to spur your thinking

and make you understand
on an intuitive level

things that are otherwise
quite abstract

in the way of physical concepts.

It's a real big part
of doing physics, frankly,

to have a deep intuition
about things

in addition
to simply doing the math.

NARRATOR:
After the first mini slide
of liquid mountain,

Iverson doubles the rainfall

to trigger an even bigger
landslide.

IVERSON:
First, we had a relatively
shallow slope failure

that's typical
in many mountainous areas.

But then after that,

we continued to add water
to the slope,

eventually triggering
a much deeper-seated failure

where the material liquefied
when it failed,

and then we got a much
larger debris flow mobilizing.

GEOLOGIST:
Here it goes!

NARRATOR:
Heavy rain and porous soil

makes the particles behave
like ball bearings.

They lose their
cohesive strength

and become liquid earth.

IVERSON:
And that, in effect,
is our attempt to simulate

what happens when you have
prolonged rain

that sets the stage
for landsliding.

NARRATOR:
Flume experiments like this one
could help refine models

to predict the length and speed
of future landslides

and even guide
search-and-recovery teams.

The immense area affected
by the Oso landslide

requires an extraordinary
effort.

More than 900 people
were involved,

many working alongside
123 rescue dog teams

to recover those presumed dead,

sifting through every inch
of the one-square-mile mudscape.

BOB VANDER YACHT:
There are still seven humans
that have not been located.

There's not
a worker out there

that is going to want to stop
doing a search

until they've found
everybody.

BROOK ALONGI:
At this point,
it's not everybody

on their hands and knees,

digging through the mud
and the sticks.

NARRATOR:
Search zones are delineated,
like an archaeological dig.

VANDER YACHT:
The efforts are very meticulous.

They're using a grid pattern.

It has an excavator
with an operator,

dog teams, spotters.

ALONGI:
And when they pick it up,
they don't just drop it;

they gently drop a little bit

and we watch every little thing
that falls out.

NARRATOR:
It's a fine-tuned protocol
using proven search tactics.

ALONGI:
In the areas that I was
searching in,

most of the two-by-fours were
reduced to pieces this big.

And then you find a couch
that's in a million pieces,

and then you find a tractor
that's broken in half.

Trucks were ripped into five,
six pieces.

Diesel trucks!

So you can imagine
what that did to people, right?

NARRATOR:
Many residents in Oso
believed they were safe,

unaware that a landslide there
could go so far.

The last landslide here,
in 2006, stopped at the river,

but in steeper terrain
like Nepal,

landslides are
an even more common occurrence.

The world's most
landslide-prone roads

wind their way through
Earth's highest mountains.

Annual monsoons and earthquakes

bring mountainsides
crashing down

with devastating results.

Nearly one-third of the world's
landslide-related deaths

happen in the Himalayas,
where, in 2007,

falling earth killed
a thousand people.

In Nepal, 29 million people
are at imminent risk.

RANJAN KUMAR DAHAL:

NARRATOR:
Geologist Ranjan Kumar Dahal

is investigating the impact
of human activity on landslides.

Many Himalayan roads are cut
into the base of hillsides.

When the slopes above them fail,
the road is blocked.

Villages are cut off
from the world.

Homes are often built
on the site of past landslides.

NARRATOR:
Terraces cut into previous
landslides,

and heavy crops,
like water-rich rice,

destabilize the slopes.

NARRATOR:
It's a system that is a recipe
for disaster.

Homes are destroyed

when the saturated terrain
fails around them.

Ranjan travels up

one of the most
landslide-prone roads in Nepal

to search for signs of villages
at risk.

He visits families
to raise awareness

so they will know
when to evacuate.

He's developed a simple model
to educate his people

so they can read the signs
of an impending landslide:

fragile soil cover,
cracks in the earth,

slumping land, and small slides
that grow over time.

His main concern is that
a massive landslide will follow

when the next big earthquake
occurs.

NARRATOR:
Rivers and roads do great damage

because they cut into already
unstable slopes.

Ranjan monitors Nepal's highways
and remote roads,

looking for signs
of slope failure.

NARRATOR:
With each monsoon,

slopes slough their materials
onto the roads below.

Constant vigilance is critical,

but Nepal, one of the poorest
nations in the world,

can only put a Band-Aid
on the problem.

NARRATOR:
Bioengineering with rocks can be
effective for shallow slides,

but for deep ones like this,

gabions won't hold
the hill back.

NARRATOR:
In a country
where trails and roads

are carved from mountains
by hand,

there's little funding
to protect people

from natural hazards.

Yet the construction
of new roads continues on,

without landslide planning.

NARRATOR:
Two months after Ranjan's
prediction,

in the heart of the monsoon,
a well-known unstable slope

turned into a rapid,
deep landslide

and buried Nepal's
major highway to Tibet.

It dammed the Sun Kosi River
and killed about 150 people.

There were very few survivors.

People around the world

share in the tragedy
brought about by landslides.

In the first hours
after the Oso landslide,

11 people are rescued
from the debris field,

all far from their homes.

911 OPERATOR:
Are there any injuries?

FEMALE CALLER:
Yes, there are people
yelling for help!

JUPP:
And we could hear screaming,

and I said, "There is somebody
screaming over there,

and it sounds like a baby."

FIREFIGHTER:
A woman with a baby.

JUPP:
Oh my god!

BLANKENSHIP:
When we heard the baby cry,
it changed the thought process.

That just sped everything up
a little bit.

I held onto that baby like that
was the only purpose that I had.

NARRATOR:
Minutes after the landslide
struck,

firefighters and EMTs arrive,
but the quicksand-like mud

renders ground rescues
nearly impossible.

BLANKENSHIP:
When we initially got out there,

it was almost like a milkshake
or pancake batter.

If you dropped something in it,
it was gone,

and we knew it was four
to five feet deep.

NARRATOR:
Thrown 750 feet from her house
and now stuck on a rubble pile

in the confines
of her crumpled couch,

Amanda Skorjanc clung
to five-month-old Duke

until she heard a sign of hope.

SKORJANC:
As soon as I heard that voice,
I screamed,

and then that caused Duke
to cry.

She was in bad shape,

and I just kept her
talking to me the whole time.

BLANKENSHIP:
I remember asking Steve,

I said, "Steve,
check the baby out."

And next thing I know,

Steve's checking the baby out
and he said, "The baby's fine."

The baby got handed off
and the baby was packed out.

The baby's fine.

ERNIE ZELLERS:
Okay.

BLANKENSHIP:
At that point,
we knew the baby was fine,

and so we're moving on to our
next patient, which was Amanda.

NARRATOR:
Extracting Amanda from her couch
took a chainsaw and many hands.

BLANKENSHIP:
We just started ripping

at the fabric
and the insulation,

got all that off,

and I remember getting
to the wire

from the back of the couch,

and we didn't have a tool
for that,

so four guys just started
pulling on it really hard.

And then we heard,
in the distance, the helicopter.

We all worked together,

and then up, up and away
she went.

NARRATOR:
The search for possible
survivors

who were driving on State Route
530 was grueling,

especially for those who were
at the center of the landslide,

the most powerful point
of impact.

Dayn Brunner's sister, Summer,

was headed west on the highway
when the landslide struck.

BRUNNER:
My sister, she left the house
at 10:30.

That would have put her
right at the worst part

of the slide at 10:45, 10:47.

My mom called me that morning.

She goes, "Well, what's going on
with the highway?"

And I said, "All we know is

there's a mudslide
down by Skaglund Hill,"

and she goes,
"Summer's in it."

It was just that
mother's intuition,

and she was just adamant
about it.

She said,
"No, Summer is in there.

You need to go get your sister."

And I figured
if she was in her car

and she had an air pocket
or something,

she's waiting for me
to come get her.

Me and my two sons walked in

and we were in there
for almost six hours.

It took us two and a half hours
to walk a half a mile.

You're in mud that's
up to over your waist,

and I'm sinking down.

We're looking through cars.

We walked past four bodies.

Two of them were covered up,
two of them weren't.

It was so eerie.

We could hear moaning,
but we couldn't decipher

if it was a person
that was trapped

or if it was an animal.

I wasn't trying to be selfish

if there were other people
that needed help,

but I was going
to find my sister.

NARRATOR:
What if predicting landslides
were possible

so that roads like this one
could be closed?

That will require a system
of meticulous monitoring

of places likely to slide.

In Switzerland, scientists are
trying to develop technologies

that will save lives.

This device uses radar beams
to measure minuscule movements

of the Earth's surface.

In the Swiss village of Preonzo,

this scar is what remains
of a landslide

physicist Lorenz Meier
was able to predict

right down to the hour.

He uses a system called InSAR

to monitor a mountain
known to be dangerous.

NARRATOR:
Geologists also use lasers,
mirrors and crack meters

to measure the mountain's
movement.

The instruments detect signs

that the slope
will soon give way,

but how can scientists tell
exactly when?

NARRATOR:
The crack meters

measured the growing gaps
between crack walls,

an ominous sign that
the top of the mountain

will soon crash
into the valley below.

Mattia Soldati,
a forestry engineer,

continues to monitor them.

SOLDATI (translated):
We decided to use these
automatic extension meters

to measure the growing gap.

One end of the instrument
is mounted

on the stable side
of the mountain,

the other on the sliding side.

The extending stick
in the middle

provides the measurement
of the growing gap.

MEIER:

NARRATOR:
The laser stopped working
when clouds set in,

another advantage of radar,

which penetrates
through weather.

InSAR allowed Lorenz
to make a precise prediction

because of the refined,

millimeter-accurate measurements
of movement.

MEIER:

NARRATOR:
Lorenz plotted his measurements
onto a digital terrain model

to show the village authorities

just how fast the top
of the mountain was moving.

The growing areas
of red and blue

indicate the top of the slope is
moving not millimeters per day,

but now centimeters per hour.

The whole slope
is about to fail.

MEIER:

NARRATOR:
In the early morning hours
on May 15, 2012,

precisely when Lorenz
and his team predicted,

the slope at Preonzo collapsed.

(rumbling)

MEIER:

NARRATOR:
300,000 cubic meters of mountain

crashed 1,000 meters
down the slope.

No one was hurt,
the highway was closed,

and no buildings were affected.

The Swiss predicted
the landslide in Preonzo,

but they can't monitor
every slope.

Roads and railways
are particularly at risk

in high mountain valleys.

In late summer 2014, a train car
plunged into a ravine,

and others were left hanging
from the rails

as a result of a landslide.

At Val Parghera,
another high Swiss valley,

radar has determined a shallower
landslide is moving slowly,

but constantly.

Lorenz has set up
a timelapse camera

to document a year's worth
of earth

creeping down the mountain.

An alarm system is in place

in the event rain causes
dangerously high debris flows

into the valley.

NARRATOR:
Over the last 30 years
in Switzerland,

landslides, not uncommon,

have caused a death toll
of just one person per year.

Close monitoring of every slope

in the world's mountainous areas
is impossible,

but bringing potential hazards
to light,

like the dangerous slope in Oso,
is clearly needed.

MONTGOMERY:
The evidence for large
landslides

that could run across the valley

was there in the Lidar data.

But just because you have data
that shows you something

doesn't mean anybody's
looked at it, processed it,

or the information
has gotten out to people

who might need to
or want to know it.

We need to understand these
failures as well as possible

with all the tools and tricks
and models in our trade

and get that kind of information

out to the people
who could actually use it:

the homeowners who may be making
decisions about where to live,

the agencies who may be making
decisions

about where to permit different
kinds of development,

where to place highways.

NARRATOR:
Five days after
the Oso landslide,

Dayn Brunner and his family
finally reached closure

in their search
for his sister, Summer.

BRUNNER:
I got a call from my sister's
best friend,

and she goes,
"We've found Summer's car."

I grabbed my son.

(crying)

I said,
"Are you ready for this?"

And he goes, "Dad, I've been
ready for five days.

Let's go get her."

By the time we got there,
there was 15 people digging.

Her face, neck up, was exposed,

and we spent the next
hour and a half digging by hand.

When we were ready
to pull her out,

I just reached down
and wrapped my arms around her,

around her upper body,
and two guys were on her legs,

and I pulled up
and they pulled up,

and we pulled her out
and put her on her tarp,

and they just let you
as a family say your goodbyes.

She was in pretty good shape,

because I had seen
about 15 bodies come out

and they were horrible-looking.

They had suffered suffocation

and other various kinds
of death,

but she was whole,
and in fact, her hands

were still on the steering wheel
when they found her.

Her foot was on the gas pedal,

and she was sitting
strapped in her seat.

The ME's office said that she
had died from percussion trauma,

so it was the sound waves
hitting her car,

basically blowing
all the glass out,

blew the roof off of her car,
the trunk lid, the hood,

but her car,
it didn't keep her alive,

but it kept her in one piece.

If there's any comfort to it
at all, she didn't suffer.

She never saw it comin'.

NARRATOR:
Summer was number 17
of the 43 people

that have all now been recovered

from beneath the one-square-mile
stretch of liquid earth.

The devastation at Oso
is a wake-up call

to the urgency of identifying
hazardous slopes,

because the more we understand
their unique physics

and exactly
when they might slide,

the more we'll be able
to protect ourselves

against one of nature's
most powerful forces.

You could wish that it would
have happened

on a Friday morning

where everybody
would have been at work

and the fatality count
would have been way down.

But, you know, it's nature.

Nature runs its course.

Captioned by
Media Access Group at WGBH
That's o access.wgbh.orgr man...

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