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Hey, smart people, Joe here.
I'm in the scablands of eastern Washington right now,
and well, that's a waterfall behind me.
It's a pretty nice waterfall,
but as waterfalls go, it's actually pretty average.
Its height, the volume of water that falls over its face,
they don't rank anywhere near the top 10 as waterfalls go.
But this waterfall does hold
one important record among all waterfalls.
It was created in what is perhaps the largest flood
to ever happen on planet Earth, at least that we know of.
Whatever you're imagining as this flood,
you need to think bigger.
Much, much bigger. (upbeat music rising)
Because the flood that created this
and the entire landscape around us is bigger than anything
that could happen on the planet today, by a long shot.
(whimsical music)
Across what is today a dry and arid landscape,
there are clues of an epic flood hidden in rocky scars
and strange land forms if you know how to read them.
The pieces of this mystery are hard
to make sense of on their own,
but together they tell a story that's,
well, almost impossible to believe.
In fact, it took decades for scientists to finally accept
that these cataclysmic events really did happen.
And in the process, this story completely changed science,
forcing geologists to totally rethink their ideas
about the powerful forces and events
that have shaped the Earth throughout deep time.
This discovery also set the stage for other discoveries,
about other violent events
that have shaped not only our planet, but others.
But we're getting ahead of ourselves.
Our story begins hundreds of miles
to the east in a beautiful river valley
where today we find the town of Missoula, Montana.
- Here we are, here it is!
- Okay. What's it?
- This is the Glacial Lake Missoula high water mark.
So, this marks the highest level
that Glacial Lake Missoula got in Missoula Valley.
So, this would've been the shore
of a giant glacial-fed lake.
- You guys know Kallie from "PBS Eons", right?
She hiked us up here to see this,
which is why I'm so not sweaty at all.
- Yeah, you gotta hike to see these high water marks.
- If Kallie and I had stood in this spot 15,000 years ago,
we'd have found ourselves in the shore of an immense lake.
At the end of the last Ice Age, the valley below us
sat beneath 300 meters of peaceful blue water.
- As far as you can see would've been basically underwater,
except for where we're standing
and the tops of some of these taller mountains,
all of it would've been underwater.
- These would've just been little pointy islands,
in the lake. - Just little islands, yeah.
- It was called Lake Missoula, a freshwater inland sea,
more than 600 meters deep at its deepest point,
holding more water than Lake Ontario and Lake Erie combined.
But, why was there a lake here?
About the past million years, massive ice sheets advanced
and retreated across the Northern Hemisphere
during natural cycles of climate change.
During the last Ice Age, an ice sheet stretched unbroken
from Alaska to today's US-Canada border.
And one little finger of that ice sheet sat here
at the end of this river valley.
And that massive mountain of ice would've been right here.
You need to picture something more like the wall
from Game of Thrones than a big iceberg.
We're talking 2,000 feet tall of ice,
30 miles wide at its widest, and the south end of it ran up
against these mountains right here,
blocking the river and forming Glacial Lake Missoula.
It was big,
really big,
Just like a stopper filling a bathtub,
river water, rain, and melted snow backed up
behind this ice dam for centuries
forming a lake covering nearly 8,000 square kilometers.
But there's just one problem, ice floats in water.
First, a few leaks began to form in the ice dam,
and with the weight of thousands of cubic kilometers
of water pushing against it, one day...
- Just boom! It catastrophically failed.
The explosion, the sound of it,
probably would've carried throughout the entire northwest.
It drained probably in a couple of days.
- It's just impossible to imagine
a 2,000 foot wall of ice like Game of Thrones style,
just like. - Like failing.
- Just it cracks. - Just gone. Yeah, yeah.
It would've been pretty spectacular to say the least.
- A glacial lake twice the size of Rhode Island
emptied in just a couple days,
and the torrent of water escaping the broken ice dam
was equivalent to more than 10 times the flow
from all the rivers on the planet.
That is insane!
This kind of sudden glacial outburst is called a jökulhlaup.
Icelandic words are awesome and kind of scary.
It's almost impossible to put into scale
the unimaginable power of these flood waters,
but right behind me, we can see proof of them.
If you've ever seen those little ripples
that form in the sand at the bottom of a little stream,
well, there's ripples at the bottom of this valley
caused by the flood waters.
It's exactly the same phenomenon
as in that little tiny stream
enlarged to the size of an entire prairie.
It's mind-boggling.
As thousands of cubic kilometers of water
emptied out of this giant bathtub
flowing more than 120 kilometers per hour,
it set off the worst and most destructive flood
that we know of in Earth's history.
We think of erosion as something happening slowly over eons,
but these ice age floods
cataclysmically reshaped the landscape
in just a matter of days.
Water swept the land clean of top soil,
every bit of gravel, every bit of sand, gone.
It even ripped away bedrock in some places.
From above, we can see the scars left by this violent flood,
branching channels and coulees carved deep into the Earth.
They give this region its nickname,
the Channeled Scablands.
And there's nowhere that demonstrates the unimaginable scale
and power of these flood waters better than here, Dry Falls.
About 50 kilometers south of the Grand Coulee Dam,
we find what looks today like a deep, broad canyon,
slowly carved into the Earth over eons, perhaps.
But that's not what happened here.
Everything you see was carved almost instantly
by the violent flood waters from Lake Missoula.
During the floods,
this was the largest waterfall in the world,
five times the width of Niagara Falls.
The water was more than 30 meters deep
as it rushed over the edge,
ripping away rock from its 120 meter face
and carrying it downstream.
Elsewhere, powerful flood surges cut deep vertical canyons
and cataract cliffs in just days.
The raging waters were powerful enough
to redirect entire rivers like at Palouse Falls.
The ancient path of this river
flowed west through the Washtucna Coulee.
But during the floods, the river overflowed its banks,
raged south, and cut this new waterfall.
All across the scablands, raging whirlpools of flood water
carved potholes and craters into the bedrock.
The floods were so powerful
they carried giant granite boulders embedded in icebergs
dropping them hundreds of kilometers
from the mountains where they originated.
This here puppy's a fine piece
of Canadian granite.
Got no place here though.
These so-called erratics are scattered
throughout eastern Washington today.
Some even settling as far as western Oregon.
But there's another mystery to solve.
Okay, when we think about eroding rocks,
that seems like something that should take thousands,
millions of years even.
How did a flood that only lasted a couple
of days do so much damage to this landscape?
Well, that's cuz it's made of a very special kind
of rock that came from another kind of flood
millions of years before the Ice Age floods.
It was a flood of lava.
All across this area massive eruptions happened
that laid down lava 2,000 feet thick in some places
and that cooled into this. Basalt.
These are giant basalt columns behind me.
As that lava cooled over decades, even centuries,
it contracted.
And as it contracted, it broke,
it fractured along these amazing geometric faces.
This one's super cool.
You can see it's like a perfect hexagon.
They're almost like beehives
for giant lava eating rock bees or something.
So when that flood came through here,
these columns were already prebroken,
ready to be swept away.
An 80 mile an hour tidal wave tsunamis of flood water.
It's also a place that rattlesnakes like to hang out.
So, I think I've been here long enough.
So thousands of years ago,
a wall of ice was violently destroyed,
emptying 20 million cubic kilometers
of water per hour into eastern Washington,
scouring and reshaping the surface of the earth,
causing eons of erosion in mere days.
And eventually emptying out into the Pacific Ocean
where huge amounts of sediment and rock from Montana, Idaho
and Washington can still be found today.
And what's crazy is this didn't just happen once.
It's now thought that this ice dam repeatedly melted
and refroze as many as 25 times over several centuries.
Each time devastating the land with epic floods.
We can see evidence that Lake Missoula repeatedly filled
and emptied in the so-called strand-lines marking the hills
around the town,
each an ancient shoreline of this ice age lake.
And elsewhere, striped deposits called rhythmites,
show layers of sand and sediment laid down
and flood after flood.
These violent events all happened surprisingly recently
in human history.
Archeological evidence tells us
that humans had already crossed
into North America by the time of the floods.
The creation stories told by the Nez Perce
and Palouse Indian tribes
even contain similar flood elements.
- We don't have a lot of human artifacts
or fossils associated with the lake, it emptying,
but we know we had animals and humans
in the area during this time.
- And then you didn't.
- And-- (laughs)
Well, I'm just saying that human eyes probably saw the lake
and experienced the effects of the flood
and the catastrophic failure of it.
And it took a lot of work,
some really smart people to go against the grain
and be like, "No, no, no, this is a catastrophic flood."
And everybody's like, "No, no, no, no, no.
"No. That's not how it happened."
- When geologists J. Harlen Bretz first proposed the idea
of the Missoula floods in the 1920s,
people thought he was nuts.
At the time, geologists just didn't think
that large catastrophic events like this really happened.
Instead, everyone figured that earth's geologic formations
were carved only by the same slow, gradual processes
still happening today like rivers, glaciers and weather.
The old slow and steady idea called uniformitarianism
now stood alongside a new idea called catastrophism,
where rapid and violent events could sometimes shape
Earth's geology in ways
that slower processes couldn't explain.
And suddenly geologists began to see catastrophism
as an answer to other unanswered questions.
Like the formation of our moon by a planetary collision
and the asteroid impact that caused the dinosaur extinction
and more.
The Ice Age floods of Lake Missoula changed the face
of our planet in violent and dramatic ways,
but they also changed science.
Our planet's shapes and scars tell stories written
in time and stone if you know how to read them.
So listen to the earth,
keep your eyes open,
and stay curious.
Thank you Kallie for hiking us up here.
And if you want to be taken
on more great prehistoric adventures where you don't have
to sweat as much as I did,
go check out "PBS Eons".
- For sure.
- And thank you to Climeworks for supporting PBS.
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That massive mountain of ice would've been--
(phone alarming)
Sportscenter update. (laughs)