Unit Washingtons Geography Topic Formation of the Columbia
• Unit: Washington’s Geography • Topic: Formation of the Columbia Plateau • GQ: How was the landscape of the Columbia Plateau formed? What role did the Great Missoula flood have in shaping the landscape of Washington? What are the contributions of J. Harlan Bretz to understanding the formation of the landscape in our region (Columbia Plateau)? To begin, watch the following video: Video: Floods and Basalt Flows Shape the Landscape
Three Factors that shaped the Columbia Plateau • 1. Lava Flows • Uplifting through fissures (cracks) in the earth’s surface between 6 to 16 million of years ago created a large raised relatively flat plateau in what is now the Columbia basin Photo of basalt pillars (near Othello Washington) formed by cooled magma. Evidence of the ancient lava flows from 6 million years ago.
• 2. Volcanic Eruptions • After the lava flows ended volcanic eruptions and the wind caused much of the Pacific Northwest to be covered with volcanic ash and dust that would become the rich and fertile soil of the Palouse region of eastern Washington. In some areas of eastern Washington, there are over 100 feet of rich top soil. Farm field in the Palouse region near Pullman Washington.
• 3. Ice Age Floods • At the end of the last Ice Age 10, 000 to 15, 000 years ago glacial lake Missoula in Montana flooded as a giant ice dam gave way. Other glacial lakes would also flood. (over 100 floods) • Floods carved impressive coulees, channels in the landscape, and carried giant boulders throughout the Columbia basin • The Prosser and Tri-Cities area was covered by water for many years. The lake left over from the great Missoula floods was called lake Lewis. • Watch the first 10 minutes of this video: https: //www. pbs. org/video/ksps-documentariessculpted-by-floods-the-northwests-ice-age-legacy/ Glacial Erratic near Chelan Washington. Erratics are boulders that floated on Icebergs during the great ice age floods and were deposited as the icebergs melted.
Notice how Prosser and the Tri-Cities area were covered by glacial lake Lewis which was formed by the Missoula and Bonneville floods.
This is a Lake Lewis high water marker located on the Badger Mountain trail in the Tri-Cities. Badger Mountain, Candy Mountain, and Rattlesnake Mountain were all islands during the ice age floods.
Journal Topic: Perseverance (Sticking with a belief action or purpose. ) • Task: Have you ever been in a situation where people challenged your opinion and ideas? Did you stick to your opinion or purpose? Do you know of anyone who has been in a situation like this? This Photo by Unknown Author is licensed under CC BY
J. Harlan Bretz is considered the “guru” (influential teacher or popular expert) of Geology in Washington State. Bretz is the first geologist to maintain that great ice age floods shaped the scablands of eastern Washington. He was doubted and ridiculed by his colleagues until he was proven right. Watch this short video: https: //www. pbs. org/video/j-harlen-bretzs-discovery-c 4 gpkg/
What did Bretz do? • He Explained how the geography of the Columbia Plateau was shaped by catastrophic glacial floods. • For most of his life other geologists were critical of his theories. Some people even called him a crackpot, yet he persisted with his theories using supportive geological evidence. • Came up with the name channeled scablands to describe the rough, jagged, landscape of much of Eastern Washington. • To support his theory about the floods, Bretz cited the existence of 200 ton erratic boulders, dry river beds, and dry water falls. • He speculated that the winding canyons were carved by great rivers. For more information on the accomplishments of Bretz, you can watch the rest of this video: https: //www. pbs. org/video/ksps-documentaries-sculpted-by-floods-the-northwests-ice-agelegacy/ (You have already watched the first 10 minutes. ) • The other extra enrichment reading assignment for this week also includes very specific information about Bretz and how the ice age floods shaped the landscape of eastern Washington. (The article: “The Great Columbia Flood: An Epic Geologic Event that Shaped Landforms and Ideas, ” by Tom Mullen)
Evidence of water on the Columbia Plateau https: //www. pbs. org/video/ice-dam-and-glacial-lakemissoula-iqoslk/
Dry Falls near Coulee Dam. Bretz maintained that these scabbed rocks were evidence of a great water fall.
Dry Falls Facts • Was one of the largest prehistoric waterfalls • During the Ice Age, the falls were 3 miles wide and 400 feet deep • No water runs over it today
Giant “Erratic” Boulder Carried by a glacial flood
The Grand Coulee is one of Washington State’s most spectacular geologic features spanning almost six miles wide in some places and 50 miles long.
Banks Lake was created when the Grand Coulee Dam was built across the Grand Coulee, damming the mighty Columbia river.
- Slides: 15