Palouse Falls, WashingtonPlunging 60 meters into the river below, Palouse Falls remains the only wat

Palouse Falls, WashingtonPlunging 60 meters into the river below, Palouse Falls remains the only waterfall in existence remnant of the colossal Missoula floods that occurred 15,000 years ago. During this time period, the massive Cordilleran Ice Sheet, stretching from the Pacific Ocean to Montana dammed up the outflow near Missoula. The ice wall failed to contain it as water overtopped it, flooding the land an estimated 40 to 100 times. During this time, 500 cubic miles of water poured into the area with a force equal to that of 60 Amazon Rivers. This flooded area is known as the Columbian Plateau (southeast Washington). This massive monumental event in geological history carved the landscape, creating river channels and waterfalls.Much of the water is gone today, but the Palouse River flows in a fissure established by these massive floods. Falling into a plunge pool below, the water pounds at the basalt foundation, eroding the areas of rock both behind the waterfall and at the base of the river. This process of abrasion creates a continuous collapsing of rock behind and beneath the water fall, in which eroded basalt is deposited downstream of the river. The subaqueous, cavern-like hole beneath the waterfall continues to grow behind the waterfall today. An excellent depiction of this occurrence can be seen in this image by the U.S. Geological Survey - http://users.scc.spokane.edu/ABuddington/g210spr04/g1/?p=2The rock formation surrounding this flow of water was created during volcanic eruptions approximately 16-17 million years ago, during which 40,000 cubic miles of basaltic lava blanketed Washington, Oregon, and Idaho. This vast layer of igneous rock was formed, creating a fine-grained, basalt covered landscape, susceptible to erosion. This is one of the reasons why the great Missoula floods were able to carve a landscape so easily. Layers of this basaltic rock can still be seen in the rock surrounding the waterfall today.–Sam J.Image Credit: Tracy Fawns, Smithsonian MagazineReferences:http://users.scc.spokane.edu/ABuddington/g210spr04/g1/?p=1http://www.parks.wa.gov/parks/?selectedpark=Palouse+Falls&subject=allhttp://www.glaciallakemissoula.org/http://vulcan.wr.usgs.gov/Glossary/Glaciers/IceSheets/description_lake_missoula.htmlhttp://eesc.columbia.edu/courses/ees/lithosphere/lectures/weathering.html -- source link

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