Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick

Flood Routes (basalt lava or water)

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

PURCELL LOBE

Ice dam, merely a small section of the lobe• three miles long

• ten miles across (broad and flat)

• 2,000 feet tall – thus holding back 2000 feet of hydraulic head which EVENTUALLY

Burst through the Clark Fork Canyon

• Ten times combined flow of all the riversof the world

PURCELL LOBE

2nd Burst through the Clark Fork

Canyon

• Ten times combined flow of all

the rivers of the world

PURCELL LOBE

Such catastrophic floods etched coulees now known as the Channeled Scablands in eastern Washington where water velocities were highest – average velocity was 65 mph. “Constricted Burst velocities” in excess of 100 mph instantaneous erosion.

PURCELL LOBE

First Effects of Flood•Inundating 16,000 sq. miles hundreds of feet deep

•Quickly stripped 200 feet of soil

•Left scabs or erosion remnants of Basalt

•STOPPED AT WALLULA GAP (constriction point) – creates Lake Lewis

•Several weeks 200 cubic miles of water per day (pressure in) to a gap that could discharge less than 40 cubic miles per day (pressure out). Velocity increases by square root of 5

Wallula Gap

Kalama (WA) Constriction (Carrolls Bluffs)

Restriction at Kalama

• Creates Lake Allison which filled the Willamette Valley all the way to Eugene

• Estimated depth was 380 feet at Eugene

• Flood waters delivered most of the silt to produce the most fertile agricultural soils in the country

Estimate Flood Levels

• 1250 feet at Wallula Gap

• 1000 feet at Dalles

• 925 feet at Hood River

• 400 Feet at Portland

• 275 feet at Clatskanie

The Draining of Glacial Lake Missoula

Coulees are gouged-out canyons in the high desert of central Washington that now carry little or no flowing water. The two most spectacular are Moses Coulee and, just to the east, Grand Coulee. Both photos are of Grand Coulee and show the region known as Dry Falls. During the height of the Ice Age Floods, a torrent of water plucked the basalt bedrock away, forming a waterfall 400 feet tall and 3.5 miles wide. (Niagara Falls, in comparison, measures one-mile wide, with a 165-foot drop.)

THE GREAT COULEES OF CENTRAL WASHINGTON

This is an area near Sprague Lake that shows pool formations that remain today as evidence of the great lakes flow across this area.

Dramatic evidence remains

West Bar, along the Columbia River near Quincy, exhibits “mega-ripples” -- ripples generated by the massive flood

First Noticed by Harlen Bretz in 1922 and published in 1923. Bretz was not warmly received as the scientific community hates catastrophism

Erosion Feature

FINAL STAGES OF THE FLOOD

Photo compliments of the National Park Service

The flood ripped away huge boulders from the underlying lava rock and carried or floated them – constriction points literally “shoot” these rocks out

Flood Debris

The Dalles constriction point makes Lake Condon

Columbia Gorge significantly deepened by flood

Kalama Narrows back up floods Willamette Valley

FINAL STAGES OF THE FLOOD

•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! Each Flood event 2-3 weeks

Each time Lake Missoula emptied the Purcell lobe continued its

southerly progression

• The highest known shorelines are found at an elevation of 4,200 feet.

Ancient shorelines on Mt. JumboMissoula, MT

13-30 feet

these ripple

marks would

dwarf any

ordinary

ripple mark

Camas Prairie ripple marks

• Lake Columbia -- – across Spokane

• Cut deep canyons, or coulees in bedrock

OKANOGAN LOBE

Dry Falls is 3.5 miles wide with a drop of over 400 ft.

Okanogan Lobe

Palouse Falls Canyon Carved out over 2000 year period

PUGET LOBE

PUGET LOBE

• 15,000 y.a.• Olympic Mountains help squeeze the ice

sheet down the Puget Lowlands• 1 mile thick• Gouged/Scarred Puget Sound lowlands

– Creates/defines Straits of Juan de Fuca– 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– North South Hills (Drumlins) in Seattle– Created very irregular coastline– Numerous islands remain

Mt. Erie (WA)