WEBVTT

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[Intro Music]

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The Pacific Northwest is famous for many 
things.

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Including huge floods.

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Floods of lava that buried almost 40%
of Washington,

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

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of scab lands.

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

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North America?

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

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the lowest point in the state.

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The basalt bedrock here,

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

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

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A flood of water from a giant lake in Utah

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

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

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A giant lake in Montana

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flowed to the cascades, got backed up
to here.

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Each of these layers representing a 
separate flood.

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The Columbia River basalts,

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the Bonneville flood,

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and the Missoula floods.

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Let's dig into together and learn,

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about huge floods in the Pacific 
Northwest.

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[ Music Plays ]

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

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

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The Columbia River basalt group,

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a pile of lava rock more then 2 miles
thick,

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is an exception to the global rule.

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Basalt lavas usually erupt in ocean 
basins,

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but these low silica lavas flooded North
America from below.

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Much like a boat with a leak.

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

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and central Siberia.

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In each case, very large volumes of fluid
basaltic magma

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

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tens of thousands of square miles.

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

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Washington and eastern Oregon,
starting 17.5 million years ago.

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

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of a tectonic hot spot,

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

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

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North American plates slowly moving over
the stationary hot spot.

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These spectacular basalt lava eruptions,

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

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each lava flood.

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

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

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to the towering cliffs 
of the Oregon coast.

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At Pasco Washington the stack of Columbia
River basalt lava flows is 16,000 ft.

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thick, more then 3 miles of lava.

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Sitting on top of a 17 million year old
landscape.

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

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

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

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and the Columbia River Gorge,

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or in the Grand Coulee,

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

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By the Ice Age floods.

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[ Music Plays ]

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

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advancing and retreating in response to
global climate.

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

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

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of ice, above present day Seattle.

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With enormous erratics left behind

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after the ice melted back.

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

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

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

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ice margin.

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

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Gorgeous glacial moraines and impressive
glacial erratics

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

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

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and sent due south, through the Grand
Coulee,

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and over dry falls.

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

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

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near present day Saint Point Idaho.

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

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

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

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

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

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

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across eastern Washington.

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Through the cascade range and reached the
mighty Pacific Ocean.

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Up to 10 cubic miles per hour.

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

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

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

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on the lake's floor.

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

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and another Glacial Lake Missoula formed.

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Which led to the next Missoula flood.

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Drama repeated many times.

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

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of times and released quickly over 
Washington each time.

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Rinse and repeat up to 100 times.

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These are slack water sediments from the
Missoula floods.

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

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Each of these is a separate Missoula 
flood.

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

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

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

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And another flood, and another flood.

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Now that's amazing.

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[ Music Plays ]

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Meanwhile, another Ice Age flood, the 
Bonneville flood,

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happened around the time of Missoula
flooding.

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

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Filled and spilled out of Utah and into
southern Idaho.

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The old shorelines of Lake Bonneville,

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

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in 1890.

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A desert under water.

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

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

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lowering of Lake Bonneville,

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

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Unlike the Missoula floods and it's ice
dam,

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

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Probably about twice as much water.

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

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

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The Bonneville water came out slower.

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

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

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Each Missoula flood lasted for days.

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The Bonneville flood lasted for weeks.

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Gorgeous deposit.

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All these rocks were deposited by the
Bonneville flood,

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just one flood, right?

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Just a few weeks all these rocks were
dropped.

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17,400 years ago.

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Sitting on top are Missoula flood
sediment,

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there are 20 different Missoula food
layers here.

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

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So how do we know this stuff?

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Carefully crafted geographic maps,

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

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erosional chasms cut by the floods

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

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left behind.

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

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

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

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that flowed millions of years earlier.

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

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flood paths of Drumheller Channels,

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and Palouse Falls.

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Tons of bedrock were hauled away by the
floods,

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as the water exploited deep cracks in
the bedrock.

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Box shaped valleys called Coulees formed,

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where the most aggressive water did the
most digging.

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

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in places.

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

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

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Lost worlds hidden in the salt bedrock.

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

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

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thrived in eastern Washington, during
the thousands of years between

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devastating lava floods that repeatedly 
buried vibrant thriving ecosystems

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in thick lava.

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

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featureless, moonscape.

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

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but does that mean that each flood
maintained

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a high speed for Montana to the Coast?

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

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Rocky's to the Pacific Ocean.

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The Ice Age floods had the same 
roadblocks.

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

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for the floods.

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

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which was the secret passage through
the cascades,

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and onto the Pacific.

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

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The bigger the flood, the larger the
Lake Lewis.

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Calm and dirt brown with suspended loose,

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which crept up neighboring river valleys.

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

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

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

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the result?

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Impressive layers of slack water sediment.

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Each layer from each Lake Lewis.

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And the surface of Lake Lewis was
full of icebergs.

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How do we know that?

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

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the icebergs drifted to the edge of the 
lake.

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

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over Wenatchee.

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

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and depth of the floods.

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

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over the Snake River Canyon?

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That's the canyon that the Bonneville
flood,

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the one from Utah flowed through,
remember?

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

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of Southern Idaho.

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

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Creating Shoshone Falls and Twin Falls.

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The water ripping through the narrow
regions of the canyon,

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dislodging the salt boulders, and
tumbling them down stream.

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Where the flood channel widened,

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the boulders were heaped into
impressive piles.

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The Bonneville flood then entered Hells
Canyon,

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the deepest canyon in North America,

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before joining the channeled scab lands
of eastern Washington.

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The deposits left by the flood give us
reach detail.

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

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

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Creating flood stages hundreds of feet
feet high behind it.

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

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

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remember, there was just one Bonneville
flood.

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

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in eastern Washington.

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100 Missoula floods!

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But there is work yet to be done.

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What's the age of each flood?

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

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mouth of the Columbia River?

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

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continental scene?

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And how did the lava stay molten for 300
miles?

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Much yet to be determined.

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With our huge floods, in the Pacific
Northwest.

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[ Outro Music Plays ]