Transcript No Slide Title

The Great Floods of Glacial
Lakes
Colonnades of
Columbia Plateau
basalt.
Rocks
cascading
into a lake
left by a
glacier
in the
Canadian
Rockies
CORDILLERAN ICE SHEET - GLACIAL
MISSOULA & COLUMBIA LAKES
• Cordilleran Ice Sheet -- 4000 feet thick
End Moraine
Retreating
Glacier
Steam
Ice
Face Tunnel
Braided
Stream
What
scientist
think it
would look
like
Ground
Moraine
Pre-glacial
Lake
Drumlin
Outwash
Plain
How Glaciers Move
• Large rocks (till)
at the base of a
glacier that have
been plucked
from the terrain
as the ice moved
over it.
The Cordilleran Ice Sheet south into northern
Washington, Idaho, and Montana
MISSOULA & COLUMBIA LAKES
• Ice Age 15,000 and 12,800 y.a.
• Near end of the Pleistocene Epoch
CORDILLERAN ICE SHEET LOBES
1 Purcell Lobe blocked the Clark Fork River
forming Lake Missoula Channeled Scabland
2 Okanogan Lobe blocked the Columbia River
(at Grand Coulee Dam) forming Glacial Lake
Columbia (Grand Coulee, Banks Lake,
Steamboat Rock, Dry Falls, & Moses Coulee)
3 The Puget Lobe scoured the Puget Sound
PURCELL LOBE ICE DAM
•Blocked Clark Fork River
•(Idaho-Montana border)
• Created Glacial Lake Missoula
• Covering 7,800 square kilometers
(western Montana)
PURCELL LOBE
PURCELL LOBE ICE DAM
Contained more water than Lakes
Erie & Ontario combined
• Held 2,000 square km. of water
• Approximately 600 meters deep
1st Lake Missoula floated the Ice Dam
• Ice dam, merely a small section of the
lobe
• three miles long
• ten miles across
• 2,000 feet tall
PURCELL LOBE
1st Lake Missoula floated the Ice Dam
• When the water behind the dam became
deep enough
– southern finger of the vast ice sheet
– popped up like ice cubes in a glass of
lemonade
2nd
•
Burst through the Clark Fork Canyon
Ten times combined flow of all the
rivers of the world
PURCELL LOBE
THE FIRST FRONT OF THE FLOOD
• Mass of water, debris, and ice 2,000
feet high
• Raced toward the ocean at 65 miles per
PURCELL LOBE
THE FIRST FRONT OF THE FLOOD
• Inundating 16,000 sq. miles hundreds
of feet deep
•Quickly stripped 200 feet of soil
•PURCELL LOBE
Such catastrophic floods etched coulees
now known as the Channeled Scablands
in eastern Washington where water
velocities were highest
PURCELL LOBE
STOPPED AT WALLULA GAP
Left scabs or erosion remnants of
Basalt
PURCELL LOBE
STOPPED AT
WALLULA GAP
•Several weeks 200 cubic miles of water
per day to a gap that could discharge less
than 40 cubic miles per day.
PURCELL LOBE
STOPPED
AT
WALLULA
GAP
• Water filled the Pasco basin, Yakima and
Touchet Valleys forming temporary Lake
Lewis
• PURCELL LOBE
FINAL STAGES OF THE FLOOD
The torrent widened and deepened the
Columbia River Gorge, baring the majestic
cliffs seen today
PURCELL LOBE
• Pushed back and reversed the flow of the
Snake River all the way past Lewiston,
Idaho.
PURCELL LOBE
• Temporary lakes formed in the Scablands
and silt, sand, and gravel settled out of the
water.
PURCELL LOBE
• Channeled Scablands
• The very dark areas
• = lakes and rivers
Missoula Floods
Picked
apart the
bedrock,
and carved
an
immense
channel
system
into the
land
PURCELL LOBE
Where did all the loess, dirt, sand,
gravel and silt end up?
Some of the material were deposited in
the Willamette Valley in Oregon
Flood Debris
Iceberg deposit (glacial erratic)
The flood ripped away huge
boulders from the underlying lava
rock and carried or floated them
Photo
compliments of
the National Park
Service
FINAL STAGES OF THE FLOOD
Each time Lake Missoula emptied the
Purcell lobe continued its southerly
progression
•Formed a new dam
•Causing the lake to refill
•Resulting in a new flood
Average of every 55 years or so for 2,000
years!
FINAL STAGES OF THE FLOOD
• Piles of rocks left behind near Eugene
were brought by icebergs broken off
the original ice dam formed by the
Purcell lobe of the Cordilleran Ice
Sheet
Up to 40 times
Flood Debris
Many layers of glacial lake sediments are
found situated on top of one another;
each layer represents a separate filling
of the lake
FINAL STAGES OF THE FLOOD
•
Not far from the present day site of
Portland, the river makes two 90
degree turns.
• Ice and debris formed a temporary dam
causing the floodwaters to spill into the
Willamette Valley as far south as
present day Eugene
Looking at the evidence
Ancient shorelines on Mt. Jumbo
Ancient shorelines on
Mt. Jumbo
Missoula, MT
• The
highest
known
shorelines
are found
at an
elevation
of 4,200
feet.
Camas Prairie ripple marks
13-30 feet
these ripple
marks would
dwarf any
ordinary
ripple mark
• Lake Columbia -– across Spokane
• Cut deep canyons, or coulees in bedrock
• Coulee south of Coulee City.
• Unlike the Grand Canyon, which was
eroded by a river, the coulees of Washington
were carved out by Ice Age floods.
Okanogan Lobe
DRY FALLS
by John Knapp
http://www.bmi.net/knapp/whitman.html
Dry Falls
Eastern Washington
Three &
one-half
miles wide,
Dry Falls is
five times
the width of
Niagara
Falls
Photo compliments of the National Park Service
Okanogan Lobe
OKANOGAN LOBE
• Soap Lake today
is known as Dry
Falls
• Skeleton of one
of the greatest
waterfalls
Okanogan Lobe
OKANOGAN LOBE
Dry Falls is 3.5 miles wide with a drop of over 400 ft.
OKANOGAN LOBE
Two Major North South Grand Coulees
* Larger Upper Coulee -a river over an 800 ft.
waterfall [4 miles Wide & 20 miles Long]
* Lower Coulee is [7 m long and about 1 mile wide]
Eroding power took pieces of Basalt rock
causing the falls to retreat 20 miles and
self-destruct
(where Grand Coulee Dam is today)
Okanogan Lobe
Grand Coulee
• This is a view below and down the channel at
• Palouse Falls.
• Can you imagine the amount of water it took to carve
Okanogan Lobe
out this canyon?
PUGET LOBE
• The Puget Lobe from the Glacier • Seattle under a mile of ice
• Glacier left marks on both the
– Cascade and Olympic mountain ranges.
PUGET LOBE
• 15,000 y.a.
• 1 mile thick
• Gouged/Scarred Puget Sound lowlands
– Cascades on east
– Olympics and Vancouver Island west
Puget Lobe
• 13, 500 y.a. receded
• Melting snow/ice = water runoff
• Caused
–
–
–
–
Pacific Ocean to rise
Flooded Puget Sound Trough
irregular coastline
Numerous islands
Bibliography
• Alt, David. Glacial Lake Missoula and Its
Humongous Floods. :Mountain Press
Publishing Company, 2003.
• Alt, David and Donald W. Hyndman.
Northwest Exposures: A Geologic Story of
the Northwest. :Mountain Press
Publishing Company, 1995.
Bibliography
• Durr, Gerald. Evidence of the Flood in
Franklin County. July 17, 2003
<http://www.nwcreation.net/articles/evidenc
eoftheflood.html>
• Knapp, John. John Knapp’s Art Gallery .
“Dry Falls, Washington”. July 5, 2003.
<http://www.bmi.net/knapp/whitman.html>