Ice Age Floods, Lake Missoula, Bonneville Flood and the Columbia River Basalts

[Intro Music]

The Pacific Northwest is famous for many
things.

Including huge floods.

Floods of lava that buried almost 40%
of Washington,

and floods of Ice Age water that
created more than 2,000 square miles

of scab lands.

What are the odds that such rare events
both happened here in this corner of

North America?

We're just south of Lewiston Idaho at the
mouth of Hills Canyon,

the lowest point in the state.

The basalt bedrock here,

the floods of lava, came out of deep
cracks that formed in response to a heat

source that's now, in the state of
Wyoming.

A flood of water from a giant lake in Utah

came all the way through Southern Idaho,
through Hills Canyon,

dropped rocks here, and the water made it
to the Pacific Ocean.

A giant lake in Montana

flowed to the cascades, got backed up
to here.

Each of these layers representing a
separate flood.

The Columbia River basalts,

the Bonneville flood,

and the Missoula floods.

Let's dig into together and learn,

about huge floods in the Pacific
Northwest.

[ Music Plays ]

The Ice Age floods have helped exposed
and incredible pile of lavas

from erupting volcanoes that are not
related to our famous cascade volcanoes.

The Columbia River basalt group,

a pile of lava rock more then 2 miles
thick,

is an exception to the global rule.

Basalt lavas usually erupt in ocean
basins,

but these low silica lavas flooded North
America from below.

Much like a boat with a leak.

They're similar flood in central India,
southern Brazil, southern Africa,

and central Siberia.

In each case, very large volumes of fluid
basaltic magma

erupted rapidly from cracks and continents
to form sheets of lava rock covering

tens of thousands of square miles.

The deep crack called fissures cracked
the North American crust in south eastern

Washington and eastern Oregon,
starting 17.5 million years ago.

Today many geologist agree that the
fissures are directly related to the birth

of a tectonic hot spot,

beneath the out south-eastern Oregon
17.5 million years ago,

and now located underneath Yellowstone
National Park in Wyoming due to the

North American plates slowly moving over
the stationary hot spot.

These spectacular basalt lava eruptions,

more than 300 distinct events punctuated
by thousands of years of quiet between

each lava flood.

Flooded and buried, the rugged inland
landscape of the Pacific Northwest.

Many of the biggest lava flows made it
from their fissures in Idaho all the way

to the tower cliffs of the Oregon coast.

At Pasco Washington the stack of Columbia
River basalt lava flows is 1,600 ft. thick

more then 3 miles of lava.

Sitting on top of a 17 million year old
landscape.

There isn't one visage to see all the
lava flows, how could you?

To truly grasp the scale of the lava stack
one has to visit scattered canyons that

expose a dozen flows at a time, like
in the Yakama River Canyon,

and the Columbia River Gorge,

or in the Grand Coulee,

which was carved just thousands of years
ago, not millions.

By the Ice Age floods.

[ Music Plays ]

During the Ice Age, a thick ice sheet
covered much of North America,

advancing and retreating in response to
global climate.

In Washington, Canadian ice crossed the
border in different places.

West of the cascade range, the Puget Lobe
filled the Puget Lowland with 3,000 ft.

of ice, above present day Seattle.

With enormous erratics left behind

after the ice melted back.

Most Puget Sound residents live on
complicated sets of Ice Age deposits.

Glacial till, glacial outwash, that
reveal ice on the move.

Advancing and retreating with glacial
licks riding the front of an active

ice margin.

East of the cascades, the Okanogan Lobe
crept into north central Washington.

Gorgeous glacial moraines and impressive
glacial erratics

have been sitting on the Waterville
plateau for at least 12,000 years.

During some of the Okanagan ice advances,
the mighty Columbia River was diverted,

and sent due south, through the Grand
Coulee,

and over dry falls.

In northern Idaho, the Purcell Lobe
combined with the rugged topography

of the Bitterroot Mountains and blocked
Montana's Clark Fork River,

near present day Saint Point Idaho.

Glacial Lake Missoula formed as glacial
melt water backed up behind the ice

dam forming a huge lake, more then 3,000
square miles of western Montana.

Old shorelines of the lake are visible
above the University of Montana.

Faint water marks first noted in 1886
by T.C Chamberlin.

The lake was 950 ft. deep at Missoula and
twice that depth in neighboring valleys.

And then it happened, Glacial Lake
Missoula breeched the ice dam and raged

across eastern Washington.

Through the cascade range and reached the
mighty Pacific Ocean.

Up to 10 cubic miles per hour.

A rate 10 times the combined flows of all
the rivers on planet earth,

surged through Eddy Narrows, and other
narrow valleys in western Montana.

When the huge lake suddenly drained,
giant current ripples were created

on the lake's floor.

And the failed ice dam was replaced by a
new one,

and another Glacial Lake Missoula formed.

Which led to the next Missoula flood.

Drama repeated many times.

Banded deposits at the bottom of Glacial
Lake Missoula show the lake form dozens

of times and released quickly over
Washington each time.

Rinse and repeat up to 100 times.

These are slack water sediments from the
Missoula floods.

We're in Tammany Barge of south of
Lewiston Idaho.

Each of these is a separate Missoula
flood.

We're 150 miles upstream from Wallula gap
that means water from Montana

made it to Wallula gap and to back up this
far up the snake river drainage.

This is one event, still falling from
the bottom of Lake Lewis.

And another flood, and another flood.

Now that's amazing.

[ Music Plays ]

Meanwhile, another Ice Age flood, the
Bonneville flood,

happened around the time of Missoula
flooding.

Lake Bonneville, and Ice Age predecessor
to the Great Salt Lake.

Filled and spilled out of Utah and into
southern Idaho.

The old shorelines of Lake Bonneville,

ancient bathtub rings above Salt Lake
city were first described by G.K Gilbert

in 1890.

A desert under water.

Once the Bonneville basin was filled to
capacity, 17,400 years ago.

The erosion of loose rocky material at
Red Rock Pass led to the rapid

lowering of Bonneville,

and the Bonneville flood surged north
into Idaho snake river plane.

Unlike the Missoula floods and it's ice
dam,

the Bonneville flood involved a lot more
water then the biggest Missoula flood.

Probably about twice as much water.

But the constriction at Red Rock Pass that
had spilled out through

was much smaller then where the ice bridge
was breached in northern Idaho.

The Bonneville water came out slower.

So while the volume of Bonneville water
was twice as large as the largest Missoula

flood, the peak discharge was only
about 1/10 of the largest Missoula flood.

Each Missoula flood lasted for days.

The Bonneville flood lasted for weeks.

Gorgeous deposit.

All these rocks were deposited by the
Bonneville flood,

just one flood, right?

Just a few weeks all these rocks were
dropped.

17,400 years ago.

Sitting on top are Missoula flood
sediment,

there are 20 different Missoula food
layers here.

So at this spot, we had 20 Missoula floods
after the Bonneville flood.

So how do we know this stuff?

Carefully crafted geographic maps,

made in the field by generations of
geologists have measured both the

erosional chasms cut by the floods

and have catalogued piles of rocks and
layers of sediment that the floods have

left behind.

Water is scarce here in eastern
Washington today, it's a desert.

But the landscape has a strong stamp of
water, and lots of it.

The Ice Age floods tore up the crust,
revealing the Columbia River salt lavas

that flowed millions of years earlier.

Leaving dramatic landmarks like the Grand
Coulee, Dry Falls, the crisscrossing

flood paths of Drumheller Channels,

and Palouse Falls.

Tons of bedrock were hauled away by the
floods,

as the water exploited deep cracks in
the bedrock.

Box shaped valleys called Coulees formed,

where the most aggressive water did the
most digging.

Rock precut and hauled off by the flood
water cruising at more then 60 mph

in places.

And there are amazing potholes drilled by
the swirling dynamics of floodwater.

Often revealed in the vertical Coulee
walls, cut by the erosive ice age floods.

Lost worlds hidden in the salt bedrock.

At the bottom of key lava flows, pillow
structures were water battled lake water,

and petrified logs, provide detailed clues
to the ancient forests and lakes that

thrived in eastern Washington, during
the thousands of years between

devastating lava floods that repeatedly
buried vibrant thriving ecosystems

in thick lava.

A landscape full of life, with each lava
burial creating a lifeless,

featureless, moonscape.

Millions of years later, each of the 100
floods made it to the Pacific Ocean,

but does that mean that each flood
maintained

a high speed for Montana to the Coast?

No, like today there are many obstacles
to negotiate on a journey from the

Rocky's to the Pacific Ocean.

The Ice Age floods had the same
roadblocks.

Wallula Gap, eastern gateway to the
Columbia River gorge was a bottleneck

for the floods.

Every drop of Ice Age flood water needed
to squeeze through the gap,

which was the secret passage through
the cascades,

and onto the Pacific.

At Wallula Gap, flood water waiting to
enter became Lake Lewis.

The bigger the flood, the larger the
Lake Lewis.

Calm and dirt brown with suspended loose,

which crept up neighboring river valleys.

The Yakama river, the Walla Walla River,
and the Snake River.

The water of Lake Lewis must have gotten
clear with each passing day.

The fine grain material falling out of the
lake and onto the lake bottom,

the result?

Impressive layers of slack water sediment.

Each layer from each Lake Lewis.

And the surface of Lake Lewis was
full of icebergs.

How do we know that?

There are large erratics all across
central Washington that mark spots where

the icebergs drifted to the edge of the
lake.

Upstream some of the largest Missoula
floods came down of Columbia River

over Wenatchee.

And downstream Wenatchee, West bar is a
classic location to ponder the speed

and depth of the floods.

You old enough to remember the media
frenzy over Evil Kneviel daredevil jump

over the Snake River Canyon?

That's the canyon that the Bonneville
flood,

the one from Utah flowed through,
remember?

Lake Bonneville spilling over Red Rock
Pass and into the Snake River drainage

of Southern Idaho.

The floods scoured canyon walls
and gouged holes in the canyon floor.

Creating Shoshone Falls and Twin Falls.

The water ripping through the narrow
regions of the canyon,

dislodging the salt boulders, and
tumbling them down stream.

Where the flood channel widened,

the boulders were heaped into
impressive piles.

The Bonneville flood then entered Hells
Canyon,

the deepest canyon in North America,

before joining the channeled scab lands
of eastern Washington.

The deposits left by the flood give us
reach detail.

Giant flood bars, more then 100 ft.
above todays Snake River,

sit in narrow stretches of Hells Canyon,
showing us where the flood got choked up.

Creating flood stages hundreds of feet
feet high behind it.

In shlock water sediments are found all
through the Bonneville flood route,

but not the repetitive shlock water
sediments, like the Missoula Floods,

remember, there was just one Bonneville
flood.

All told, 100 different layers of shlock
water sediment have been documented

in eastern Washington.

100 Missoula floods!

But there is work yet to be done.

What's the age of each flood?

Is a more complete record of the Ice Age
flood sitting in the Pacific Ocean at the

mouth of the Columbia River?

And with the floods of lava, why did such
pure oceanic lava flood a

continental scene?

And how did the lava stay molten for 300
miles?

Much yet to be determined.

With our huge floods, in the Pacific
North West.

[ Outro Music Plays ]