Name: How 7,000 Years of Epic Floods Changed the World (w/ SciShow!)
Uploaded: 2021-05-01T09:05:07.000Z
Duration: 10 min 26 s
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In the vast, arid landscape of Eastern Washington lie the traces of an ancient disaster.

Outside the city of Spokane, massive scour marks run through the rocky ground, creating

a strange terrain known as the scablands.

A bit to the west, a channel has been carved into the Earth that's as deep as a forty-story

Elsewhere, miles of rolling hills run across Washington, Montana, and Idaho, resembling

These features are all the lingering remains of an epic geological mystery that took nearly

Now, every great mystery requires a great detective, and geologist J Harlen Bretz was

He researched these strange features in the early 1900's and soon concluded that features

like these could only have been made by water.

But he also knew that a flow of water that could transform the land so drastically would

It must've been a flood, of almost biblical proportions.

When Bretz presented this hypothesis to fellow geologists in 1927, he was met with ... skepticism,

But ultimately, his research would reveal one of the most powerful and bizarre episodes

And as a result, it would revolutionize the way geologists understand the world today.

Because, Bretz was right: This landscape was the result of flooding.

Instead it was dozens of major, devastating floods that took place over the course of

more than 7,000 years, forever changing the landscape of the Pacific Northwest.

What Bretz had discovered was evidence of floods that can only be described in one word:

When Bretz first began studying the weird landscape of the Northwest in the 1920s, there

was a certain school of thought that most geologists followed.

It was known as uniformitarianism, the idea that the present is the key to understanding

In this view, all rocks, landforms, and other geological features can only have been created

And except for the occasional volcanic eruption, or river overflowing its banks, all modern

So to these geologists, the scablands of Washington could only have been created by glaciers,

and the ripples must be deposits of what the glaciers had slowly scraped away.

Because, the effects of glaciers had been observed around the world.

And through the lens of uniformitarianism, they seemed to most closely resemble the features

But Bretz had studied glacial geology, too, and he knew what glaciers could do.

And to him, the features he saw just didn't fit.

Instead, they looked like scaled-up versions of what happens after a big flood.

For Bretz, the most obvious evidence of flooding was the shape of the canyons in the Scablands

These canyons, also called coulees, have flat bottoms and steep, vertical walls - very different

from the U shape of valleys that are carved by glaciers, or the V-shaped valleys made

One especially large coulee, called Dry Falls, appeared to have formed a massive waterfall

over 100 meters tall and 3 and a half kilometers wide; that's twice as tall, and five times

But water doesn't just remove things; it also deposits things.

And Bretz saw that the landscape was littered with boulders weighing up to 200 tons, having

tumbled miles away from their sources, like pebbles on a beach.

He also noted massive ripples in the earth, and gravel bars up to 90 meters high, all

typical of deposits made by powerfully flowing water.

Finally, Bretz knew that these features couldn't be related to glaciers, because of what was

missing: the huge ridges of deposited sand and gravel called moraines, which form

Only one tiny moraine was found in the scablands, not nearly enough evidence for the giant glaciers

that would have been required to carve features this big.

But despite all of this evidence, other scientists weren't convinced that this strange landscape

They argued that humans had never seen a flood anywhere near as big as the one Bretz proposed,

so they were reluctant to believe that such a thing was even possible.

Uniformitarianism explained a great deal about geology, and epic floods just didn't fit into

What giant floods did fit into was the geological mindset that Uniformitarianism had replaced:

An older school of thought known as catastrophism.

Catastrophism was an idea put forward in the early 1800s by French scientist Georges Cuvier.

This theory explained all geologic formations as evidence of large, sudden, unpredictable

events -- often events that were referred to in the bible -- like celestial impacts,

enormous volcanic eruptions, and ... massive floods.

So no matter how good his evidence was, Bretz's hypothesis seemed extremely outdated.

And there was still one really big question that Bretz couldn't answer.

If all this flooding really happened, then where'd the water come from?

And this was something that puzzled Bretz himself.

He initially thought that the water had come from some melting glacier.

But he couldn't explain how the glacier had melted fast enough to produce so much

It turns out, Bretz was looking in the wrong place.

But someone else knew where the water came from.

This half of the mystery was solved by Joseph T. Pardee, a geologist with the U.S. Geological

Pardee had attended a conference where Bretz presented his hypothesis about the Ice Age

megaflood, and watched as Bretz defended his claim against a room full of skeptics.

And more than 10 years earlier, Pardee had been working in Western Montana, where I am

now!, and where he'd found evidence of an enormous, Ice Age lake that had since disappeared.

Distinctive lines he saw high on the hillsides.

These lines form small benches, much like the shorelines of a reservoir.

So Pardee figured that these ancient shorelines were formed by an ancient lake whose source

was the Clark Fork River, which still flows today through the valley below.

This giant lake came to be known as Glacial Lake Missoula, named after the town -- which is also my

hometown! -- where Pardee saw those lines.

But a reservoir requires a dam, and a lake this size would've needed a big one.

So what had dammed the river to form the lake, and what happened to the dam?