Nova (1974–…): Season 32, Episode 11 - Mystery of the Megaflood - full transcript

The Channeled Scablands in Washington state defied conventional explanations for their formation for decades. Little by little evidence mounted for an old theory that was rejected by the scientific establishment. It involved glaci...

Are you wondering how healthy the food you are eating is? Check it -
Monument Valley...

the Grand Canyon...

Niagara Falls...

These ancient wonders
show how nature's forces

have shaped the face of our
planet on a vast time scale...

how great landmarks are
the work of millions of years

of slow, imperceptible erosion
by wind and water.

But here, across 16,000 square
miles of Washington State,

abrupt rips and scars in the
landscape defy this explanation.

What could have formed
these tall canyons

and immense dry waterfalls?

What could have gouged out
these gigantic potholes?

The forces unleashed
here created

one of the earth's
most enigmatic landscapes.

For more than a century,

scientists have been grappling
with this geological mystery...

descending through thousands
of years of earth history

in a struggle to uncover,
layer by layer,

how this landscape was formed.

Now the clues point
to a sequence of events

culminating in a massive
natural catastrophe.

You would have heard

this tremendous roar coming
long before you saw anything.

The earth would have shook.

This evidence suggests we have
drastically underestimated

the powerful forces
that shape our planet.

It suggests

that this world
can create cataclysms

far more powerful
than we ever thought.

Tonight, re-created for
the first time in 15,000 years,

the colossal cataclysm

that carved out a landscape
in the blink of an eye.

"Mystery of the Megaflood,"
next on NOVA.

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is provided

by the Howard Hughes Medical
Institute, serving society

through biomedical research
and science education.

Major funding for NOVA
is also provided

by the Corporation
for Public Broadcasting

and by PBS viewers like you.

The peaceful, flat farmland
of Washington State.

But after hundreds of miles,
it changes,

and in the distance a very
different landscape appears...

gorges, some
almost 1,000 feet deep...

a waterfall,
five times wider than Niagara

but without any water...

weird holes
in the valley floors...

strange layers of silt and ash.

And over the whole area,
huge boulders are scattered

as if a giant
had dropped them there.

Few places on earth are
as mysterious and controversial

as the Channeled Scablands

that lie just 200 miles
east of Seattle.

For over a century, scientists
have been struggling to explain

what forces could shape
this unique place,

but for much of that time, they
were unable to account for it.

When we see

a landform or a group
of landforms, we rely

upon our knowledge as to how
similar landforms were created.

So the geologist
is always thinking

of the origin
of a particular feature.

However, there was one landscape

that really defied
the understanding of geologists,

and, of course, that landscape
was the Channeled Scabland.

Then a series of clues
began to fit together

to finally explain
this bizarre landscape.

And it came about
from the study of rocks.

In geology,

we are really
looking for evidence,

for features in the rocks,
on the landscape.

It's very similar
to what a detective does

looking for clues
at a crime scene,

and those clues are fit
into a pattern,

and ultimately a culprit
is associated

with that crime scene.

It's wonderful to be flying

over one of the most interesting
parts of the United States.

Even the first explorers
and first settlers

who came in this area

recognized this as truly
remarkable topography.

And they realized
that this was something

like the earth having been
subjected to wounds and sores,

so they called this "scabland."

But you can't really get
a sense of the scale of this

unless you get out
onto the landscape yourself.

For a long time, it was assumed
that the Scablands' features

would have taken
millions of years to create.

One obvious way
this could have happened

was by the gradual erosion
caused by rivers.

After all, some of the most
dramatic landscapes in the world

have been scoured out by rivers.

A lot of the features in this
valley do appear at first sight

to be related to rivers that may
have come through the valley.

But some features require
fast and violent river action,

while others, like
this huge hill of gravel,

appear to have been laid down
by large, slow-moving rivers

over millions of years.

And these mysterious layers
look like the result

of a giant river
flooding again and again.

And that's actually really
what's been puzzling geologists:

How could a river
have deposited those features

and yet carved out

such a wide and deep
and long and sheer canyon?

The rivers and lakes
in the Scablands today

could not have sculpted
this landscape.

This water is part
of a modern irrigation system

and was not here when
the Scablands were created.

The only river big enough
and old enough is the Columbia,

which is 50 miles away,

and there is no evidence it ever
flowed through the Scablands.

But there's another reason
to rule rivers out.

No river in the world can form
what you are about to see.

You will not find these
anywhere else on earth.

These enormous potholes

are one of the strangest
geological features

on the planet.

If I was on the bottom of
a big river, like the Columbia,

I might find some potholes

that were maybe a few feet
across, a few feet deep.

But this feature,
this rock basin,

of which there are hundreds
in the Channeled Scabland,

is about ten times as big
as the potholes that we find

in even a large river
like the Columbia.

It's very clear just
from the size of the feature

that this was not made
by normal river processes.

This revelation
turned the Scablands

into one of the most
perplexing geological mysteries.

But if not rivers, then
what formed this landscape?

Boulders like this one pointed
toward another possible culprit.

How could this 100-ton giant
have been dumped

on the edge of this
thousand-foot precipice?

It's made of granite,

and granite is not native
to the Scablands.

But granite boulders
of many different sizes

are scattered erratically
throughout the area;

indeed, they are known
as "erratics."

There is one force on earth that
can put this boulder up here,

and it is not a river;
it is something else...


Ice can carve through solid rock
and can help build mountains.

20,000 years ago,
during the last ice age,

massive sheets of slow-moving
ice called glaciers

pushed gradually down from
Canada towards the Scablands.

Glaciers move down valleys

carving out new landscapes
as they go.

They rip out rocks
from the valley floor,

and these erratics
then travel within the ice,

sometimes for hundreds of miles,

until they're left behind
when the ice melts.

But erratics were not the only
clues pointing to glaciers.

When a glacier carves out
a canyon,

it cuts through lots of little
valleys on either side,

leaving them hanging far
above the main valley floor.

There are some classic

glacial-like features.

On the ridge on the horizon,
there are hanging valleys,

where the cliff cuts
a depression.

In glaciation, the glacier
enters a valley, it enlarges it,

and it cuts off the tributaries,
leaving them hanging.

So it was natural
to have as the hypothesis

that glaciation may be
the origin

of some of these large features
in the Channeled Scabland.

Yet again, it looked as if
the culprit had been found:

Surely glaciers, working
over thousands of years,

must have created
this strange landscape.

But there was a problem:

The ice sheets
that flowed down from Canada

during the last ice age
never reached the Scablands

So the two main theories

to explain the gradual formation
of this landscape

just didn't work.

River erosion could not explain
giant potholes,

and ice was too remote
from the Scablands

to create these hanging valleys.

Geologists, it seemed, were back
where they had started.

Each time they attempted
to explain

the riddle of this tantalizing
landscape, they failed.

There was, however,
one last theory

that claimed to offer an answer.

Unfortunately, it struck
those who first heard it

as completely outrageous.

During the 1920s,

a geologist named J. Harlen
Bretz outlined a theory

of what he thought had really
happened to the Scablands.

But Bretz's theory defied
all scientific convention.

He claimed the Scablands
were not the result

of a slow geological evolution,
but of an enormous catastrophe

that had happened
almost overnight.

For years,
Bretz traveled the Scablands

examining the landscape.

Eventually one feature
would clinch his argument,

although it would take him
decades to recognize it.

From ground level, these shapes
don't make much sense.

Bretz must have walked

over thousands of those things,

but they're so big in the field,
he had no idea what they were.

He just... He didn't guess
what they were.

Bretz would not see aerial
photographs of these hills

for many years.

But we can see from the air

how these shapes begin
to look like ripples,

a giant version of the ripples
left behind on the beach

by the sea.

Even without
this key observation,

the years Bretz spent
patiently examining rocks

and other features
of the Scablands

convinced him only
a vast volume of water

could account
for all the evidence.

In his mind,
the entire landscape,

which had once been
a flat plateau,

was created
in a single giant flood.

But as Bretz well knew,
his geological colleagues,

understanding that the earth
was billions of years old,

firmly believed that landscapes
such as the Scablands

must have gradually formed
over long periods of time.

It was this orthodox view

that Bretz now seemed
to be challenging.

Since the 1820s, geologists had
come to think, on good evidence,

that landforms... most landforms
and most deposits on earth

had formed over long periods
of time by ordinary processes

of rivers and ocean waves
and what have you.

Bretz comes and offers
this immense catastrophe

altering the landscape
essentially overnight,

and it was just... didn't square

with the way geology had been
put together at the time.

On the 12th of January, 1927,

Bretz prepared to address
a specially convened meeting

of fellow scientists
in Washington, D.C.

This was his big chance
to sell his outlandish theory.

The 423rd meeting of the
Geological Society of Washington

is now called to order.

Bretz was proposing something
completely unheard of:

a body of water
up to 900 feet deep

raging though the Scablands

and then flowing off
into the Pacific Ocean.

Over 500 cubic miles of water...
Great flow depths.

Now, no gradual process is
responsible for this landscape.

I am forced
by the field evidence...

By what I have observed
with my own eyes...

To come to this hypothesis.

It is clear
from my field evidence

that the Columbia River
swollen in size

could easily have cut dry falls.

To any self-
respecting geologist,

this sounded too much
like a biblical flood.

They dismissed Bretz
out of hand.

This did not happen overnight,

but over many
thousands of years.

To suggest otherwise
is ludicrous.

The implication was very clearly

that Bretz was committing
a kind of heresy

and that he should listen

to these elder statesmen
of the science

and rethink his hypothesis.

Even if you were convinced
by his unbelievable idea,

Bretz still had a problem.

Where did the water come from?

And Bretz can't tell them
where the water came from.

It's one of the big problems
with... with the whole idea.

To convince his colleagues,
Bretz needed a source.

How could so much water,
traveling at ferocious speeds,

suddenly appear out of thin air?

No one among the top geologists
gathered that day

could imagine a source
for this heretical flood.

Well... almost no one.

Sitting in the audience
is J.T. Pardee.

Pardee supposedly leans over
to a colleague and says...

I know where
Bretz's water came from.

That this formation...

But it would be
more than a decade

before Pardee
revealed his secret.

Long-continuing, gradual...

During that time,

Bretz remained firmly
in the geological wilderness.

But Bretz would not give up,

and his theory would
eventually return again

to take the world
of geology by storm.

This is Missoula, Montana.

It lies 250 miles east
of the Scablands.

Few who live here
would ever suspect

that this peaceful place
was once the center

of an epic confrontation
between water and ice.

The sheer scale
of this confrontation

is hard to imagine,
but evidence of its true extent

lies scattered
on hillsides for miles around.

For a long time, no one could
work out what made these marks.

It was only
when geologists discovered

some scrapings on a rock

that an unusual idea
unexpectedly emerged.

These marks...

Scratches, as it were,
on the bedrock...

Represent the erosion
of a large glacier

that moved into this valley.

This evidence gave rise
to the possibility

that the glacier created a lake
by damming a river.

These watermarks were formed
by the waves of this lake

splashing against the shoreline
of these hills.

This glacier came from Canada
during the last ice age

to reach what is now Idaho.

Looking at a larger scale,

the ice moved down
the valley from Canada

and filled this whole valley
from one side to another.

It ran into
the mountain in front of us,

and thus blocked the river
valley off to the left.

Clark Fork River, which
still runs through this valley,

confronted a wall of ice that
was at least half a mile high,

and an amazing 23 miles wide.

The river began to back up
against this wall of ice

and fill the valley with water.

Eventually the lake
of trapped water grew bigger

than Lakes Erie
and Ontario combined.

It was this lake
that made these watermarks,

and if it were still here today,
it would drown Missoula, Montana

in well over
a thousand feet of water.

The volume of water backed up
behind the ice was vast,

an astounding
520 cubic miles of water

that became known to geologists
as Glacial Lake Missoula.

This valley was once the bottom
of Glacial Lake Missoula,

and it holds vital clues

to solving the mystery
of the Scablands.

But what could it have to do
with a place

that's 250 miles away?

It was here in this valley
that Joseph T. Pardee...

The man who didn't speak up
at Bretz's meeting...

Made an important discovery.

He knew from the watermarks
that there was once

an enormous lake here,
but there was no evidence

that it had ever been
anything but static...

until he noticed these ripples.

Those are huge ripples,

like ripples
on the floor of a stream,

but here instead
of being inches high,

they're ten, 20,
30, 40 feet high

and spaced 200, 300 feet apart.

They're enormous.

It was when he saw these ripples

that Pardee came up with
his own extraordinary theory.

He proposed that Lake Missoula
had somehow emptied,

and as it poured out,

the lake water pushed up
the gravel on the valley floor

to create these giant ripples.

And he looks around

and sees these other things
that goes with it.

There's that great bar of gravel
with a steep front to it.

There's the pass up there
that is sharply eroded.

There are these rocks
all over the ripples

that indicate
high speed of current

And there was something else
about the ripples

that Pardee noticed:

They seemed to point
straight towards the Scablands.

Here's a huge body of water,

and it's discharging
at a fantastic rate

headed right towards
Bretz's Channeled Scabland.

Pardee's discovery
of the ripples was crucial.

At last he'd come up
with a possible source

for Bretz's giant flood.

But there was one question

he and his colleagues
couldn't answer:

What caused the lake
to empty in the first place?

Vital clues would eventually
come from 3,000 miles away

in another
extraordinary landscape.

This is Iceland...

one of the world's most
geologically active landmasses,

constantly rocked by earthquakes
and volcanic activity.

This island on the northwestern
tip of Europe

is home to strange
lava-filled formations,

and it also has more glaciers

than all of those in Europe
put together.

Matthew Roberts' work
examining glaciers

for the Icelandic
Meteorological Office

has cast a whole new light
on Glacial Lake Missoula

and its disappearing water.

What you are looking at now
is a modern-day wall of ice.

It is the head of a glacier,
a smaller version of the one

that created Lake Missoula
over 15,000 years ago.

This glacier is massive.

It's about 300 feet thick,
but that's tiny in comparison

to the glacier that formed
Glacial Lake Missoula,

which was at least
ten times thicker.

In this example here, the ice
has flowed across the valley

to the other side,
forming a plug.

This is exactly the same setting

as what would have occurred
at Glacial Lake Missoula.

When glacial ice blocks
the flow of a river

and water builds up
behind the ice,

scientists call it an ice dam.

From his work
studying ice dams here,

Matthew Roberts and his
colleagues have come up

with an extraordinary

for how Glacial Lake Missoula
might have emptied.

It has to do with what goes on

deep inside these
enormous mountains of ice.

His theory is based
on data from seismometers

which monitor tiny ice cracks
opening hundreds of feet

deep inside
this massive glacier.

These cracks signify

that the glacier is behaving
in a brittle manner,

that the ice is fracturing.

Just like the fractures
that we see behind us here,

these crevasses have opened up
due to stresses inside the ice,

and the crack is heard
by the seismometers.

Matthew Roberts was driven
to do this work

not by an interest
in Lake Missoula,

but by an urgent need
to understand a disaster

that happened
on his own doorstep.

In 1996,
a wall of water cascaded

through southern Iceland,
causing incredible devastation.

It was the result
of an ice dam collapsing.

After years of analysis,
Matthew eventually worked out

the process
that caused the dam to fail.

Normally, water freezes
at zero degrees centigrade

and forms ice.

But deep at the base
of an ice dam,

the sheer amount of pressure

stops the water molecules
from expanding.

If they cannot expand,
then the water cannot freeze.

This results in what is known
as supercooled water,

which can stay liquid at
several degrees below freezing.

Then this highly pressurized
supercooled water

begins to force its way
into tiny cracks in the ice.

Water under this much pressure

behaves in some very
unexpected ways,

especially in such
intimate contact with ice.

This is the first small step

in a chain of events
that can end in cataclysm.

Once supercooled water
has begun to trickle

through these cracks, the
flowing water alone is enough

to trigger a very
peculiar process.

This moving water creates
tiny amounts of friction.

This friction releases energy
in the form of heat.

As the water moves through
the glacier, it melts the ice.

Soon, minute cracks can become
giant ones, several feet across.

More water can escape,

the tunnel enlarges
very quickly,

but then suddenly
the dam would have failed,

and bang, the whole dam
would have collapsed

and a massive wall of water
kilometers wide

would have swept down valley.

This process caused
the 1996 Icelandic flood,

and scientists now believe
it was responsible

for what happened
thousands of years ago

at Glacial Lake Missoula

when a half-mile-high wall
of ice suddenly collapsed,

allowing the entire lake
to empty.

From these new findings,
we can reconstruct

just how Glacial Lake Missoula

sent 2½ trillion tons of water...
Nearly half of Lake Michigan...

Surging across
the American Northwest.

First, river water built up
for years behind the ice dam.

Then, as it reached depths
of several thousand feet,

the pressure grew,

forcing molecules
of supercooled water

into cracks at the base of the
Glacial Lake Missoula ice dam.

What started
as a minute trickle of water

quickly hollowed out a series
of tunnels in the ice

that fatally destabilized
the whole structure.

Then, as the sheer weight
of water became too much,

the ice dam
literally exploded...

leaving a gaping hole
a mile or more wide,

through which a sea
of lake water erupted.

You would have heard

this tremendous roar coming
long before you saw anything.

The earth would have shook.

Imagine the loudest noise
you've ever heard,

and multiply that
by a thousand times.

The sheer speed and volume
of this incredible mass of water

churned up those huge ripples

and left behind watermarks
as a record of its vast size.

This one cataclysmic event sent
trillions of gallons of water

at ferocious speeds
towards the Scablands.

This is how scientists believe
the ice dam collapsed

and how
Glacial Lake Missoula emptied.

But could this single event
have created

all the extraordinary features
in the Scablands?

How could a rushing mass
of water create canyons

that look as if they were eroded
over millions of years,

like this one,
known as Dry Falls,

20 times the size
of Niagara Falls?

How could water transport
these giant erratics

that are normally carved out
by glaciers?

And how could it form these
strange potholes found here

on such a monumental scale?

To test whether a single flood
coming from Lake Missoula

could really have done all this,

scientists have built
their own mini-Scablands.

Here, the Earth
Surface Dynamics team

at the University of Minnesota

has constructed a scale model
of the Scablands

and poured water over it

to represent the failure
of Glacial Lake Missoula.

Here it comes.

The rushing water doesn't simply
disperse over a wide area;

it gouges out channels

and then erodes them
into extraordinary shapes.

It is only when
the water is turned off

that the significance
of these shapes becomes clear.

We're seeing the same
essential set of processes.

In fact, it's one
of the remarkable things

about these natural systems...

is that the same fundamental
sets of processes can occur

across a very wide range
of scales.

They're what we call

For years, scientists argued

that the features
of the Scablands

could not have been
formed overnight.

But this model clearly shows

miniature versions of the
canyons found in the Scablands.

Just like the real ones,

they look as if they were
gradually eroded.

In fact, they were carved out
in seconds.

But can the scientists also show

how these strange potholes
were made?

This water tunnel demonstrates

the effects of water
moving at high speeds.

An object in the tunnel

a hard outcrop of rock.

At first, the water flows
around the object

without any apparent effect.

But then they turn up the speed.

A stream of minute bubbles

When those bubbles burst,

they burst with immense force
against the object.

As the speed of water
increases further,

the bubbles collapse
with ever greater intensity.

The process, slowed down
nearly a hundred times, reveals

a long twisting thread emerging
from the metal object.

It is in this high-speed
vortex of bubbles

where the secret to the flood's
incredible power lies.

So, if you look at this,

the first thing we see here is
this very strong vortex here.

So you got like
a sledgehammer effect.

Every time one of these forms
and collapses,

bang, you got a sledgehammer.

So, could bubbles really gouge
holes out of solid rock

to resemble the potholes
in the Scablands?

Slowed down 80 times,
this experiment shows

solid rock being drilled out
by the power of bubbles.

But what would this have
looked like during the flood?

As the flow of water
from Lake Missoula surged

through the Scablands,

it would have hit
some hard outcrops of rock

creating a vortex of bubbles.

Within seconds,

these bubbles would drill
through cracks in the rock

and the turbulent currents would
then scour out huge potholes.

With this last mystery solved,
it does seem plausible

that a single giant body
of water could create

all the features
of the Scablands.

So it is now possible
to complete the reconstruction

of the incredible events
that took place

on a fateful day
15,000 years ago.

The immense pressure
of supercooled water

fatally destabilized the ice dam
at Glacial Lake Missoula.

Then massive chunks of ice
within the dam began to fall

into the raging torrent until
the whole dam just gave way.

The collapse of the ice dam
released a sea of water.

This water then traveled
up to 60 miles per hour,

rushing headlong
towards the Scablands.

It took only a few hours

for the water to reach
this once-flat landscape.

In places, the water was
a staggering 800 feet deep.

As this volatile torrent flowed
ever more quickly,

it gouged out miles of rock.

It carved out cliffs
and canyons,

including the massive feature

that is known today
as Dry Falls.

huge underwater tornadoes

were blasting out potholes,

the bubbles that formed
these tornadoes

imploding with enormous force

and penetrating deep
into the bedrock below.

As the chunks of ice
from the original glacier

were carried huge distances
by the floodwaters,

the boulders
they contained within

were randomly flung aside.

When the floodwaters receded
and the icebergs melted,

they would reappear
scattered all over the Scabland.

After a tumultuous journey,

this muddy torrent
surged out to sea

along the floor of the Pacific
until it came grinding to a halt

over 1,000 miles
from its point of origin.

It had only taken
a few hours to get there.

80 years ago,

J. Harlen Bretz shocked
the geological establishment

with an idea
that was seen as heresy.

But over the years,
more and more scientists

gradually began to accept
his theory.

Well, I think Bretz
was absolutely delighted

to see the vindication
of his ideas.

I think
it all culminated in 1980,

when he received
the highest medal

of the Geological Society
of America, the Penrose Medal,

which was the final
and ultimate recognition

that he, in his
catastrophic flood hypothesis,

had generated one of the great
ideas in the earth sciences.

It was left to later generations
of geologists

to work out the details of how
the giant flood had happened.

Their research
not only confirmed

Bretz's outrageous hypothesis,

but has recently revealed
that if anything,

Bretz was not outrageous enough.

For there may have been
more than one giant flood.

This final twist in the tale

centers on one of the classic
features of the Scablands

that has long intrigued

this canyon
with its many layered deposits.

Richard Waitt has been studying
these deposits

for over 20 years.

It was assumed
that these layers were formed

by changes in the speed of one
giant flood, known as pulses,

but that was before
he discovered something odd:

a white line
within the sediments.

This is what caught my eye
first time down in the canyon.

It's an ash layer
from Mount St. Helens.

We've analyzed it.

Once you become familiar
with these ash layers,

they become old friends,
so I knew what this was.

It's an ash layer
from Mount St. Helens.

It's about 15,000 years old.

Mount St. Helens,
in Washington State,

erupts regularly.

The ash from the eruption
can spread

over thousands of square miles,
as it did some 15,000 years ago

near the time
of the Scablands flood.

At first,
it was thought that the ash

had fallen into the water

and drifted down
into these layers.

But could a layer of ash
really sink

through hundreds of feet
of turbulent floodwater

to form this
amazingly neat, clear line?

This whole column would be
full of mud and sand and silt.

And to have something
settle through it

and come out like this
is impossible.

This suggested
something completely new...

that all these layers
weren't laid down together.

It's clear evidence
that periodically

during the accumulation
of this sediment

that there had to have been
dry land.

And the implication of that

is that there wasn't
just one giant flood.

Perhaps there were many.

After one superflood swept
through the Scablands,

the floodwaters drained

and there was a period
when the land was dry.

It was then the ash fell,

before another superflood hit
and laid more deposits on top.

The only way to know
whether this theory is true

is to date the layers,

as Kathleen Nicoll
is now painstakingly doing.

This is a really thick
sequence of rocks.

And by looking at the age

of the bottommost unit
that we can sample

and then the topmost unit,

we'll be able to see
if it's one great big flood

that stacked up
a lot of sediment,

or whether it was
a series of floods

coming in
every few years, perhaps,

over many thousands of years.

It will be years before
Kathleen has dated every layer,

but her first results show

that the top and the bottom
layers of the canyon

are 20,000 years apart.

We thought that there was
just one flood,

but now with these results,
we can say with certainty

that this area
has been repeatedly hit

by cataclysmic megafloods
again and again.

With these latest results...

A culmination of over a century
of geological investigation...

It now seems that gigantic
floods as well as smaller ones

were a regular feature of this
landscape during the ice age.

Incredibly, ice dams collapsed
and re-formed

in a cycle that rocked
the Scablands again and again.

Despite the conflict

between a catastrophic view
of the Scablands

and the standard view
of gentle continuous change,

we now know the truth
is somewhere in between.

There were huge catastrophes

that carved out
these giant landscape features,

but they were part
of a cycle of floods

that repeatedly swept
through this landscape.

The Channeled Scabland

is one of the most
fascinating landscapes,

and the tremendous
catastrophic floods

were probably
the most spectacular things

that happened on the planet.

This legacy is
part of human history,

and I think that it's just
an exciting scientific problem.

On NOVA's Web site,

explore the giant potholes,
granite boulders

and rippled ground
of the Scablands for yourself

and trace how experts unraveled
the mystery of the megaflood.

To order this show or
any other NOVA program

for $19.95 plus
shipping and handling,

call WGBH Boston Video
at 1-800-255-9424.

NOVA is a production
of WGBH Boston.