cordilleran ice sheet 15-20,000 years ago – 4000 feet thick
TRANSCRIPT
![Page 1: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/1.jpg)
Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick
![Page 2: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/2.jpg)
Flood Routes (basalt lava or water)
![Page 3: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/3.jpg)
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
![Page 4: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/4.jpg)
![Page 5: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/5.jpg)
PURCELL LOBE ICE DAM
•Blocked Clark Fork River
•(Idaho-Montana border)
![Page 6: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/6.jpg)
• Created Glacial Lake Missoula• Covering 7,800 square kilometers
PURCELL LOBE
![Page 7: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/7.jpg)
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
![Page 8: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/8.jpg)
2nd Burst through the Clark Fork
Canyon
• Ten times combined flow of all
the rivers of the world
PURCELL LOBE
![Page 9: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/9.jpg)
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
![Page 10: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/10.jpg)
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
![Page 11: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/11.jpg)
Wallula Gap
![Page 12: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/12.jpg)
Kalama (WA) Constriction (Carrolls Bluffs)
![Page 13: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/13.jpg)
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
![Page 14: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/14.jpg)
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
![Page 15: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/15.jpg)
The Draining of Glacial Lake Missoula
![Page 16: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/16.jpg)
![Page 17: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/17.jpg)
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
![Page 18: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/18.jpg)
This is an area near Sprague Lake that shows pool formations that remain today as evidence of the great lakes flow across this area.
![Page 19: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/19.jpg)
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
![Page 20: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/20.jpg)
Erosion Feature
![Page 21: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/21.jpg)
FINAL STAGES OF THE FLOOD
![Page 22: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/22.jpg)
![Page 23: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/23.jpg)
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
![Page 24: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/24.jpg)
The Dalles constriction point makes Lake Condon
Columbia Gorge significantly deepened by flood
Kalama Narrows back up floods Willamette Valley
![Page 25: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/25.jpg)
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
![Page 26: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/26.jpg)
• The highest known shorelines are found at an elevation of 4,200 feet.
Ancient shorelines on Mt. JumboMissoula, MT
![Page 27: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/27.jpg)
13-30 feet
these ripple
marks would
dwarf any
ordinary
ripple mark
Camas Prairie ripple marks
![Page 28: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/28.jpg)
• Lake Columbia -- – across Spokane
• Cut deep canyons, or coulees in bedrock
![Page 29: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/29.jpg)
OKANOGAN LOBE
Dry Falls is 3.5 miles wide with a drop of over 400 ft.
![Page 30: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/30.jpg)
Okanogan Lobe
Palouse Falls Canyon Carved out over 2000 year period
![Page 31: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/31.jpg)
PUGET LOBE
![Page 32: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/32.jpg)
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
![Page 33: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/33.jpg)
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
![Page 34: Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick](https://reader036.vdocuments.site/reader036/viewer/2022062515/56649ccb5503460f9499515f/html5/thumbnails/34.jpg)
Mt. Erie (WA)