Missoula Floods '14

As a meteorologist, I'm also interested in many of the other 'ologies.  Today, class, it's geology...with the Ice Age thrown in.  The bible is, as always, David Alt's classic, "Glacial Lake Missoula and its Humongous Floods".  I have the book with me and am referencing it constantly as I drive through North Central Washington.  Yes, I love nurse logs.   Another natural thing I love is glacial erratics.  Here's a nice one, a basalt stone dropped by an Ice Age glacier on the east side of the Columbia River near Lake Chelan.

For the first time I visited a little known gorge in central Washington called Moses Coulee.  When the Okanagan glacier dropped south and blocked the Columbia River about 15 thousand years ago, it dammed the river and at first diverted it into this coulee, between the current river and Grand Coulee.  Moses Coulee thus took the flow from glacial Lake Columbia for a time, and probably for several of the early Missoula floods, which sent huge walls of water through the coulee and sculpted it to its current configuration.  The talus slopes consist of chunks of basalt that have peeled off the cliffs since the end of the floods in the coulee.

The huge layers of basalt that make up the walls of Moses Coulee are products of catastrophic events themselves.  15 to 17 million years ago, much of Oregon and Washington were overrun by massive basalt flows, which deposited hundreds of feet of lava over thousands of square miles in months or a few years.  Imagine if something like that happened now...wow!  It would be massively disruptive and dangerous.

Blow up this pic for better detail.  Here the columnar basalt in Moses Coulee has been contorted by movements in the earth, and of course battered by the Ice Age floods.

Eventually the glacier that blocked the Columbia River infiltrated Moses Coulee, blocking it and diverting the Columbia yet farther east into Grand Coulee.  Jameson Lake here developed in a depression just behind the snout of the Ice Age glacier in the coulee. 

The tan colored ridge is the glacial moraine in Moses Coulee, about three miles north of US highway 2.  It's composed mostly of small rocks.  This ridge marks the farthest advance of the Ice Age glacier in the area.  Hard to envision a massive wall of ice on an 87 degree day, surrounded by sagebrush.  But it happened...only about 15 thousand years ago, which is yesterday in geologic time.

The Lizards are into geology!  After all, their fossil ancestors are found in the ancient rocks.  Here they're contemplating erratics near Dry Falls.

And here is Dry Falls, in Grand Coulee.  The falls developed when the Columbia River was blocked by glacial ice farther west, creating Glacial Lake Columbia, which rose over 500 feet above the riverbed, then flowed into Grand Coulee and thence over the falls toward the south.  Under normal conditions, the Falls were impressive enough...3 1/2 miles wide, 400 feet high, dwarfing Niagara.  But when the Missoula Floods came down, the volume of water was such that Dry Falls became a mega white water rapids!  About a class 40 on the scale of 1 to 5.  Over several thousand years the falls eroded about 20 miles of basalt from south to north, winding up here.  What a spectacle that must have been!

I saw a film at the Dry Falls visitor center, and the scientist was talking about the massive erosive power of the water from Lake Columbia and the Missoula floods, and wondering where the rocks wound up after being carved off the edge of the falls.  They wound up here, near the modern town of Soap Lake, just south of the mouth of Grand Coulee, where the floodwaters fanned out.  Of course, as they fanned out, they became shallower and moved more slowly, and the rocks they were carrying came to rest.  Blow up this pic and you can see many medium sized rocks lying in the field.  Most are basalt, and were probably moved only 30 miles or less.  The lighter colored rocks are granite, and were swept from near the site of Grand Coulee Dam down here, a good fifty miles.