You are here

Ice Age Floods National Geologic Trail: The Rest of the Story


This map from the Ice Age Floods Institute gives some perspective to the size of the trail. The lines running through the blue are proposed routes you'll be able to tour when they're completed.

The Ice Age Floods National Geologic Trail is the first of its kind. It's a trail whose hallmark is geology. And what geology that is.

As Professor Bob explained back in June, this "trail" is actually a network of routes in Washington, Oregon, Idaho, and Montona designed to interconnect historic sites, parks, and other facilities interpreting the geologic consequences of the Glacial Lake Missoula Floods. Those floods actually were a series of several dozen immense floods resulting from the sudden draining of a giant ice-dammed lake many thousands of years ago, floods that scoured vast amounts of sediment and rock from the eastern Washington scablands, created many unique landforms, and carved the impressive Columbia River Gorge. And all of this was done so quickly it defies the imagination.

Writer Eric Wagner was so mesmerized by the creation of this landscape that he convinced the editors at High Country News to let him spend a few days in Washington state getting to better know the trail. And then he convinced them to let him write 3,000 or so words describing the geology at hand. Here's just a snippet to whet your appetite:

Most geological parks focus on contained, stationary features. This trail, the first of its kind, will be something else -- an attempt to put rock in motion, to give it narrative, a start and a finish. All of which raises the question: How exactly do you get people to see movement in something as permanent-seeming as stone?

Here's the no-frills version: About 15,000 years ago near the end of the last ice age, a lobe of the Cordilleran Ice Sheet, which covered much of Alaska and western Canada, stretched south to what is now Missoula, Mont., blocking the Clark Fork River with an ice dam over 2,000 feet tall and 2,200 feet thick. The backed-up river formed an enormous lake, called Glacial Lake Missoula, which held over 500 cubic miles of water -- more than is held by Lakes Erie and Ontario combined. Over the decades, the water wormed its way through minute cracks in the ice, probing and wearing away at the base of the dam as only water can until the entire structure became critically unstable. When at last it failed, it did so spectacularly. A towering wall of water blasted out and rampaged across Idaho and eastern Washington at up to 80 miles per hour. Over 3,000 square miles of land were covered to a depth of 1,000 feet. The torrents peeled off columns of rock and boiled up at choke points along the Columbia Gorge, back-flooding so furiously that the Snake River ran in reverse. The waters rumbled on to present-day Portland, still hundreds of feet deep, backing up again at the narrows near Kalama, Ore., and forming another temporary lake in the Willamette Valley, before roaring on, past Astoria, another 100 miles or so to the edge of the Pleistocene coast, and then into the Pacific, spewing sediments out along the ocean floor as far south as California.

Glacial Lake Missoula took only two days to drain; the floods probably lasted two weeks. After they subsided, the ice dam started to re-form. Then, after 30 to 50 years, it failed again. The process repeated itself, perhaps more than 100 times over the next 3,000 years, before the Earth warmed and the Pleistocene Epoch ended. According to geologists, the Ice Age Floods, as they eventually became known, may have been the largest floods the Earth has ever experienced.

Mr. Wagner spins a good yarn. Better still when you realize it's all based on fact. This is a story of geology woven through with human history and modern-day vistas. It's a good story. One worth reading before you head out in search of the trail.


Thanks, I'd read the HCN story and wanted to research the trail, and here you did it for me. :)

I highly recommend Glacial Lake Missoula and Its Humongous Floods by David Alt, for even more in-depth reading. I read this a couple years ago in preparation for driving I90 from Missoula to Seattle. It was a lot of fun to look for sites along the highway that Alt mentions in the book, ancient shorelines of the lake high above the highway north of Missoula, etc. Standing in the Columbia National Wildlife Refuge on a dusty 100 degree day in August, it was almost refreshing to picture a wall of glacial water descending upon me.

I also just picked up Bretz's Flood: The Remarkable Story of a Rebel Geologist and the World's Greatest Flood by John Soennichsen a couple weeks ago. Haven't read it yet, but it focuses on the human history Kurt alludes to. It's mostly a story about the geologist J. Harlan Bretz, and I would presume it illustrates the tragedy of how cruel scientists can be to one of their own.

Yeah, once you have an idea of what to look for, it's *really* obvious.

Must look for the Alt book, if only to support someone using 'humungous' in a title.

Yeah, Sharon, I thought that took some literary guts to put "humongous" in the title of a book dealing with a clearly scientific topic.

A modern, smaller version of the glacial lakes is now in the making in Alaska at the terminus of the Hubbard Glacier. A tongue of the glacier appears close to closing the outlet of Russel Fjord, a branch of Yakutat Bay.

Add comment


This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

National Parks Traveler's Essential Park Guide