Wednesday, October 15, 2014

The great Glacial Lake Missoula Floods

As we left Yellowstone, Chris had plotted our course to follow the geologic history of the great floods that swept from western Montana through central Washington and to the coast.

During the last great ice age, glaciers moved down to block the Clark Fork River, creating what was believed to be the largest lake ever impounded by an ice dam.  It wasn't until the 1990s that an even larger example was found in Siberia.    The blockage of the Clark Fork occurred about where the present day town of Sandpoint, Idaho and Pend Orielle Lake are.   The water backed up, flooding the huge valley where present-day Missoula, Montana, stands, creating a lake roughly the size of Lake Ontario.   As the water backed up behind the dam, it reached a depth of 2000 feet, eventually weakening the ice and causing the dam to fail catastrophically.

This didn't happen just once.  It happened many times, roughly between 15,000 and 13,000 years ago. At one point, 36 water level marks have been counted.

Our first good look at the water marks was behind the University of Montana in Missoula.The top shoreline was 950 feet above our heads.

As we traveled along the Clark Fork River, we saw further evidence of the forces of water.

One of my favorite spots along the route was Camas Prairie, a unique valley in western Montana (on a map of Montana, look northwest of Missoula to find route 28 off Montana Hwy 200).  Here giant ripples as shown in the three photos below, were the important clue in understanding what took place here.   What was extraordinary was to image that the water was about 800 feet above where we stood at the top of the pass where I took the third photo in this series.

Large boulder left behind.  the white object is a bit of the spine of a deceased cow, just to give a bit of perspective on size.

Looking through the Camas Prairie.  Although the antidunes are not plowed, the lower, flat area of  the valley includes a number of large ranches.

A huge debate began in 1923 when J Harlan Bretz first proposed that the Scablands of central Washington State were created by a huge flood.   His colleagues, who at that time subscribed to the notion that geology is a slow process, met his proposal with derision.  (It wasn't until much later that he was vindicated.  Fortunately Bretz was long lived, and in 1962 geologists wired him to let him know they were now convinced of the accuracy of his theory.He also received the highest award among geologists.)

One of the things that supported Bretz was the work of Joseph T. Pardee.  And it was aerial photos of the Camas Prairie which supported his believe that a huge body of water, created by an ice dam, caused the cataclysmic flooding that Bretz believed caused the Scablands.

The ripples run as much as 35 feet high.   Hydrologists explain that there are two main kinds of ripples in stream beds.  One is formed from slower moving water which leaves ripples called dunes.  Fast flowing water leaves "antidunes" called such because the steepest slope faces into the current.  The ripples at Camas Prairie are antidunes, proof of not slow erosion, but a huge flood.

As we moved further to the west, we watched more of the phenomenon of the "Scablands," the name given by early settlers to the steep coulees (those deep ravines, often dry, and called by other names such as arroyos, in other parts of the country), or steep rocks, islands of hard rock, and tortured terrain.  We spent a night at Palouse Falls, photographing it in the evening and again in the morning.  this falls is still running.  It is in terrain carved by the cataclysmic floods of Glacial Lake Missoula.  The falls is 180 feet high and the top of the cliff is 477 feet and water rushed over the top of that level.

 Our next stop was also a falls, but one that is now dry.

Our next stop was also a waterfall; a dry one.   Dry Falls, between present day Soap Lake and Coulee City was once the largest waterfall in the world.  As we drove towards the Falls, we passed spectacular walls of basalt.

The falls extended from about where the man in the red shirt on the platform at left is standing, all the way across to the far wall on the upper right hand side of the photo...the wall in the rear, not the small rock face in front of it.  

We drove the car down to the basin at the bottom of the falls.  Here you seem some of the hard rock which survived the torrential flows of water while softer rock was torn away.  Even these rocks had huge chunks forced apart and carried downstream.

Also at the bottom of the falls.

Downstream of Dry Falls, water now impounded.

Further north, we stopped at Grand Coulee Dam.  The dam, a major project during the Depression era and beginning of World War II, utilizes some of the area cut away by the Glacial Lake Missoula Floods.

We did do a short side trip from Palouse Falls to the Snake River near Little Goose Lake Dam and Lock.   Here the water from the Glacial Lake Missoula continued its course from the Snake to the mighty Columbia and then to the Pacific.  Maybe someday we will continue the journey.  I have traveled up the Columbia Gorge, but did it admiring the scenery and the story of the Lewis and Clark Expedition and the cultures of the Native American peoples of the region.  Now I would add the geological history to the wonder.

As we left Palouse, we stopped by this grain elevator.  The Palouse County, except where it was eroded by the floods, contains which silt which has blown there, to be deposited in rich farmlands where grains are raised today.   At Washtucna we stopped at the local watering hole for a great breakfast and friendly conversation with the cook\waitress\bartender who makes great omelets, and one of the local farmers.
My motorhome gives a sense of scale to the grain elevator.  

Our journey ended in Spokane, WA.  Chris had only an evening, but got to meet RVing friends, Sherry and Jim White who have a home there.   I put him on the plane home early that morning and he was at a meeting in Richmond, CA by late morning.  I spent another two nights parked in Jim and Sherry's driveway and got more time to visit.  Other RV friends also have a home nearby and so Marilyn and Jerry came over for a visit.  It was fun getting caught up.

And from there I headed south and west, across Oregon.  But those adventures await another blog entry.

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