Ice Age Floods of the Pacific Northwest

ISS011E13607: Lake Pend Oreille on 26 September 2005 at 17:54:50 GMTIt's raining again in North Idaho. After a snowy winter and wet spring, the Pack River is running high. The broken pilings from the old logging railroad bridge near the store are covered with water, something that always happens during a high water year. This is not unusual for North Idaho, however, and other years have been much higher. Old timers will be happy to tell you about the flood of 1948 when water crept up the streets in Sandpoint almost to the courthouse. And that flood paled in comparison with the one in 1894 that washed out many sections of railroad tracks around Lake Pend Oreille and forced the Northern Pacific to ship passengers and freight via steamboat between Ventnor and Clark Fork. The flood that year set the historic high water mark that remains unchallenged.

But all of these disasters were just a proverbial drop in the bucket compared to the unbelievably huge floods during the last part of the Ice Age that ended around 14,000 years ago. As the Cordilleran ice sheet moved south, smaller lobes of ice extended into what are now the states of Montana, Idaho, and Washington. One of these blocked the Clark Fork River where it flows into Lake Pend Oreille and backed water up all the way to Missoula, creating a lake that covered 3,000 square miles.

From time to time this ice dam failed and released catastrophic floods that shaped the landscape we see today, from western Montana to the Pacific Ocean. When the dam broke, the impounded water rushed out so fast that geologists estimate that the massive Glacial Lake Missoula drained in just a few days. These floods scoured eastern Washington, rushed along the Columbia River, and spilled back into the Willamette Valley of Oregon before emptying into the ocean. The water moved at an incomprehensible volume and rate, calculated as several times the combined flow of all the rivers of the world today. The lake refilled and emptied dozens of times until a warmer climate caused the ice sheet to retreat northward permanently.

There are still signs of these giant floods seen in today's landscape. Some indications are subtle, like the lake level lines on the bare hillsides around Missoula, while others are dramatic, like the Dry Falls in eastern Washington which at one time dwarfed Niagara Falls. Congress provided special recognition for these features when it established the Ice Age Floods National Geologic Trail in 2009. Although still in the planning stages, the trail will include interpretive sites along 700 miles through four states in the Pacific Northwest. It will be managed by the National Park Service.

If you're looking for more information on the Ice Age floods, geologist Bruce Bjornstad offers good graphics and a birdseye view that can be downloaded as a pdf.

Aerial photos, taken from space, provide a chance to follow the path of the floods across the Idaho Panhandle and into eastern Washington. NASA astronaut John L. Phillips, now a Sandpoint resident, took a series of these photos from the International Space Station. They are available for viewing and/or downloading (no charge) at www.bonnercountyhistory.org. They include:

Lake Pend Oreille

26 September 2005 at 17:54:50 GMT

ISS011E13608: Priest Lake on 26 September 2005 at 17:54:54 GMT

Priest Lake

26 September 2005 at 17:54:54 GMT

ISS011E13126: Spokane on 15 September 2005 at 22:45:40 GMT


15 September 2005 at 22:45:40 GMT

ISS011E13606: Coeur d’Alene Lake on 26 September 2005 at 17:54:45 GMT

Coeur d’Alene Lake

26 September 2005 at 17:54:45 GMT

There are a number of good books with additional information on the Ice Age floods. The newest one, On the Trail of the Ice Age Floods: The Northern Reaches, by Bruce Bjornstad and Eugene Kiver, is available from Keokee Books in Sandpoint.

The Ice Age Floods Institute, which helped push through the legislation establishing the first National Geologic Trail, has a lot of good information on its website.

In the meantime, if you're planning to fly to the conference in Spokane, grab a window seat so you can see the unique channeled scablands of eastern Washington, miles and miles with prominent "scabs" of basalt where the floods washed away the soil and exposed the underlying rock.


At-risk features of the Floods

Hello, Nancy,

I googled 'ice age floods preservation' and found your article. Good on you, mate. Some of the high-value features of the Floods are likey to be erased or degraded by developement soon. I'm desperately looking for someone whose wider circle of acquaintances might include someone who either knows of a preservation trust that would preserve these features, or would be willing to take on this task.

Someone has bulldozed a trail across the giant current ripples below Moses Coulee, probably to show the property to developers. It's on the main highway - high volume - berween Wenatchee and Quincy. Developed for education, it has the potential to place the imprint of GCRs in the brain of thousands of tourists yearly. And our brains, too. Once the pattern is in the head, then one is able to recognize GCRs elsewhere.

The hospital in the Tri-Cities is selling its land on Wallula Gap, to finance a new hospital.

Know anyone?


Ice Age Floods Institute

Wiley -

I appreciate your concern for the giant current ripples and hope that you can find others in your area who share your interest in them.  I suggest that you contact the Ice Age Floods Institute (www.iafi.org) to find the local chapter nearest you.  Folks in your chapter will have the knowledge and contacts to help you.  IAFI's support was key to the passage of legislation authorizing the National Park Service to establish the Ice Age Floods National Geologic Trail.  You may also be able to get some assistance from the National Park Service at Coulee Dam.

Good luck!


your article

Great article, Nancy!
With your very latest info I want to go do more exploring....

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