[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 Hells 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 Hells 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 expose 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 towering cliffs of the Oregon coast.
At Pasco Washington the stack of Columbia River basalt lava flows is 16,000 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 flow layers, 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, silt 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 Lake 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 where lava 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 Northwest.
[ Outro Music Plays ]