Hello young people.
The Ice Age Floods at Wenatchee, Washington.
The Columbia River and the foothills of the
Cascades.
There's a great Ice Age Floods geology story
here.
And the Columbia River is part of it.
Mainly deposits though, we're not talking
about ripping up the ground by the floods
here.
We're talking about depositing material out
of the Ice Age floodwater.
Upstream from Wenatchee, the Okanogan Glacier
an ice-sheet came down from Canada and blocked
the Columbia.
Sending water into Grand Coulee and over Dry
Falls and protecting Wenatchee from the power
of these Ice Age Floods.
But there were times during the Ice Age that
the Okanogan was not there and the Ice Age
Floods could come all the way down
the Columbia River.
Around the horn and down over the city of
Wenatchee.
65 Mile an hour water, 1,000 feet deep!
There's more to the story than that.
The Columbia Valley is narrow upstream from
Weanatchee cut into stubborn metamorphic rock
called gneiss.
There's also a narrow Columbia Valley downstream
from Wenatchee, cut into basalt.
But here at Wenatchee the basin is open it's
broad, so the Ice Age
floodwater coming down the Columbia slowed
here, filled this basin and waited their turn
to exit south through the narrow canyon.
That means that we had water creeping up neighboring
valleys, as well as depositing truly giant
flood bars.
The most famous of which is Pangborn Bar,
deposited
on the inside curve of the Ice Age Floods.
A pile of rock 600 feet high.
The high-water mark above Pangborn Bar, 1,700
feet in elevation that means we had so
much water here that the water started to
slowly creep up to the west, the Wenatchee
River Valley.
Quiet slack-water over Cashmere, Dryden, Peshastin.
Ice Age floodwater getting all
the way up into the Cascades as far as Leavenworth.
Have you heard this before?
Heck, there's ice at this time up at Leavenworth
coming out of the Icicle drainage.
And yet, we've got Ice Age floodwater lapping
up against that glacier.
That's quite a story, what evidence do we
have for that?
We've used Ice Age flood erratics and rhythmites
to reconstruct this part of the story.
Erratics, light-colored boulders
scattered on the hillsides here in the Wenatchee
River valley.
Up to 300 feet above the river are those boulders,
up to 600 feet above the river here at Wenatchee,
we've got
these ice-rafted erratics.
Telling us where the high-water mark was of
this quiet bathtub water working it's way
up the Wenatchee River.
In fact, all the beautiful orchards that are
in the floor of the Wenatchee Valley are on
Ice Age Flood deposits.
Those are the rhythmites, fine-grained chalky
sedimentary materiel deposited at the bottom
of this
Ice Age water.
Each rhythmite talking about an individual
flood event.
And maybe not all of the water surging up
the Wenatchee River Valley is coming from
the north.
Moses Coulee is not very far away.
And there was a big broad giant flood bar
that sealed off the mouth of Moses Coulee
that trapped water and sent more slack-water
upstream and into the Wenatchee area.
The Ice Age Floods at Wenatchee, Washington.
