Sunday, April 23, 2017

Bridge of the Gods...a little Geology

Here are two odd stories about the Columbia River.  The first one is one where when white settlers first got to the area, Native Americans told the story of the Bridge of the Gods, a stone arch bridge crossing the Columbia River.  There were many versions of the story, including one where Mt. Hood, the male and Mt. St. Helens, the beautiful female got in a fight, and she stomped her foot and broke the bridge.

Here's what geologists think.  At this narrow spot on the Columbia River (looking from the Oregon side to the Washington side - you see the current Bridge of the Gods and the rain),

there was a horrific landslide about 500-700 years ago.  The landslide swept across the Columbia River blocking it, and making a lake which quickly backed up.  If you can imagine the bit of mountain that's no longer between these twin peaks, that's what slide across the river.   The river pushed the bottom of the slide out and rushed through, creating a natural bridge.  No one really knows how long the bridge lasted before it fell in.

This areal view from a kiosk picture shows the twin peaks and the landslide area.  To the bottom right of the picture you can see the current Bridge of the Gods.  I skillfully put my shadow in the picture so you could see it better :-0  Notice how the slide pushed the whole river down from its original straighter channel.

This is from the Washington side of the river looking south to Oregon.  Imagine this with a natural stone bridge.  Pretty cool.

The stones created a rapid in the Columbia River called the Cascades.  To help settlers get around the area, they first made wooden tracks, then had a train to do a portage service, but they wanted boat traffic to be able to navigate the dangerous rapid.  So they built the Cascade Lock, which allowed boats to get around the rapid.  Here's a picture of the old lock.  After Bonneville Dam was built downstream, it flooded the area and they no longer use this lock.

There's lots more to tell, including the story of the Missoula Floods, the largest floods ever to occur on the planet, which swept right through the Columbia River Gorge during the ice ages.  Ice dams backed up an estimated 600 cubic miles of water, which broke throught and swept through Washington, flooding it.  Geologists estimate that the depth of the flood waters at Bonneville, just downstream of these pictures was about 650 feet.  Learn more about the Missoula Floods and Bridge of the Gods here.

Here's a cool picture showing something that I'll talk more about later.  It's a Native American fishing platform for dipnetting.  The platforms are placed overhanging rapids.  If you look, you can see the long aluminum pole of the dipnet.  The hoop of the net is about 3-4 feet in diameter.  In essence, you wait till a salmon swims up in the eddy, and catch them in the net.

Here's a couple on the other side of the lock wall.

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