Geology of the Columbia River Gorge

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Geology of the Columbia River Gorge

• a.k.a THE GORGE ROCKS!

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Prepare for a catastrophic journey
Yikes!
that will help you understand the formation of
the Gorge and see some key locations.
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How did the Gorge form???

• Two major factors
• Basalt lava flows
• Missoula Floods

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Basalt Flows

• About 17.5 mya, fractures in the Earths crust
  near the southern end of the Wallowa Mountains
  (in NE Oregon) released basaltic lava
• There are three major theories about how this
  the Earths crust fractured
• 1. Hot spot released lava (similar to the hot
  spot that has formed the Hawaiian islands)
• 2. Meteorite impact fractured the crust
• 3. Cracks in the crust formed due to pressure
  from large amounts of magma (chunk of subducted
  plate broke off, creating a large amount of magma
  in a relatively short amount of time)

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Over the next 11 million years or so, different
flows of basalt covered an area of about 63,200
mi2
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What were these basalt flows like?

• Imagine a lava flow about 100 feet high and more
  than 50 miles wide its speed ranged from 3-10
  mph and was 2000 F
• Repeated flows stacked on top of one another
• In the central part of the Gorge, the basalt
  layers are more than 2 miles thick

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Vista House at Crown Point State Park
A good place to learn more about the geology
of the Columbia Gorge and take some splendid
photos
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First named by Lewis Clark, this is the eroded
remnant of an ancient volcano
Beacon Rock
OR
WA
Vista House at Crown Point
Columbia River
Basalt that flooded the Columbia River channel
about 14.5 mya, cutting across basalt laid down
in earlier eruptions
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Layers of basalt are evident on the Oregon side
Its me again! Vista House!
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and on the Washington side
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Ancient floods make hiking dangerous
Many steep drop-offs are the result of the
carving of the Gorge by catastrophic floods
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Why are there so many waterfalls in the Gorge?

• The Glacial Lake Missoula Floods cut away
  streams, causing the water to suddenly fall over
  tall outcroppings of basalt

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Latourell Falls
Shepperds Dell
WATERFALL POP QUIZ
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Wahkeena Falls
Multnomah Falls
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Horsetail Falls
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Some words of warning concerning the pursuit of
geology

• Dont take pictures as a driver

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Some words of warning concerning the pursuit of
geology

• Dont take pictures as a driver
• Dont fall off cliffs

But look at those cool rocks down there
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Some words of warning concerning the pursuit of
geology

• Dont take pictures as a driver
• Dont fall off cliffs
• Watch out for flying logs

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Bibliography

• Unless otherwise noted, your amazing teacher took
  the photographs seen in this presentation ?
• Geology of the Columbia River Gorge. USDA Forest
  Service. January 3, 2006 
• lthttp//www.fs.fed.us/r6/columbia/forest/geology/
  index.shtmlgt. 
• (slide 5)