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Multnomah Falls
Photo: Jason Kenworthy

More than 600 ft of Columbia Plateau basalt forms the precipice for Multnomah Falls. During the great ice age floods, floodwaters would completely inundate the gorge.
 

The Columbia Gorge traces the paths of two monumental floods, one of flowing rock and one of flowing water. The now hardened basalt layers of the Columbia Plateau forms some of Oregon’s most dramatic scenery, and comprise the most well-studied flood basalt deposit in the world. The Columbia Gorge owes much of its natural wonder to deluges of water that carved away at the basalt layers during the waning stages of the last great Ice Age.

In this window, learn about the unimaginable amounts of basalt that erupted from giant cracks in northeastern and southeast Oregon. Some flowed all the way to the coast starting 17 million years ago and ending about 6 million years ago. Much later, 15,000 years ago, tremendous ice age floods helped carve the gorge. Today, waterfalls and waves continue to sculpt the massive basalt flows.


Digging Deeper: For more information, visit these websites.

Columbia River Basalts (US Geological Survey):

http://vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlateau/framework.html


Columbia Gorge Ice Age Floods (US Geological Survey):

http://vulcan.wr.usgs.gov/Glossary/Glaciers/IceSheets/description_lake_missoula.html


In the 1920s, geologist J Harlan Bretz, began amassing evidence for the ice age floods. It wasn’t until decades later that geologists finally accepted his spectacular field evidence for such floods. Learn more about him and the quest to understand the curious landforms of the Pacific Northwest created by these floods:

Ice Age Floods Institute:
http://www.iafi.org/floods.html

NOVA television program featured the story of these “megafloods”:
http://www.pbs.org/wgbh/nova/megaflood/


Digging Deeper: For more information, give this sample of books a read:

Wild Places by Terry Toedtemeier and John Laursen (2008 OSU Press [http://oregonstate.edu/dept/press/]) features historic photographs of Columbia Gorge (1867-1957)

Geology of Oregon, 5th Edition by Elizabeth L. Orr and William N. Orr (2000, Kendall/Hunt [
http://www.kendallhunt.com/]) Professors at the University of Oregon, the Orr’s have been writing about Oregon’s geology for decades.

In Search of Ancient Oregon by Ellen Morris Bishop (2003, Timber Press [
http://www.timberpress.com/]) Take a photographic journey through time and see Oregon’s ancient places.

Windows
Assembling Oregon
Geological Resources
Geology and People
Volcanoes of Oregon
Oregon on Shaky Ground: Earthquakes and Landslides
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