Oregon State University

College of Earth, Ocean, and Atmospheric Sciences

Alumni Field Trip: Tracing the Route of the Missoula Floods

—By Peter Clarke

November 27, 2012

This August, 2012, 16 alumni, friends of OSU, and faculty (as well as 'Geo dog' Luca Bratsi) participated in a five-day field trip that followed the route of the Ice-Age Missoula floods from their source in Montana to near their final destination in Portland. This was the third alumni field trip, which has been held every other year. With the success of each one, the field trip is well on its way to becoming a tradition that allows alumni, friends, and faculty the opportunity to see great geology and share in some wonderful experiences.

The group met in Missoula, Montana, on August 14, and had a fine dinner at the Flathead Brewery.

The morning of August 15 started with an introductory overview of the trip and a discussion of the main highlights that the group would see along the way. Here the group was told about the great Glacial Lake Missoula that formed in the Clark Fork drainage of Montana and Idaho due to an ice dam that formed just northeast of Spokane. Periodically the ice dam gave way, releasing the lake waters in a matter of hours, with the resulting flood rushing out over Spokane and across central Washington, down the Columbia River, and ultimately into the Pacific Ocean. To grasp the amount of water involved, the group was told that it was equivalent to 10-20 times all of the world's rivers combined flowing along its flood route for 2-3 weeks.

Following this introduction, the group spent the rest of the day looking at the record of glacial Lake Missoula, ending the day in Sandpoint, Idaho, where the ice dam had blocked to Clark Fork River to form the lake.

August 16 started with the group visiting the sites where the great floods first emerged from the collapse of the ice dam. They then headed west to one of the most startling sites formed by the floods, known as Dry Falls, where there are four major alcoves eroded into Columbia River Basalt (CRBs), extending ~ 5 km across and each with a 120 m drop. As the name implies, they are now completely dry, but at the time of the floods, they would have been filled with rushing water that likely would have been heard for miles in any direction.

The group then spent the afternoon looking at glacial deposits from the lobe of the Cordilleran Ice Sheet that occasionally blocked the westerly route of the floods, forcing the waters to head south across central Washington where they left their erosional signature on the landscape known as scablands.

On August 17, the group followed the flood path down the Grand Coulee, where the floods had carved a huge canyon (coulee) into the CRBs, exposing fantastic columnar jointing. There was some truly spectacular scenery as well as geology, and the pace of the trip was slow to take it all in. By mid-afternoon, it was getting very hot (mid-August in central Washington), so the group headed south to the Tri-Cities. After being treated to a special song written (and sung) by Anita Grunder just for the occasion, the group headed to Carmine's Italian restaurant, where they were treated to great home-style Italian food.

The group spent the morning of August 18 heading back east to look at some of the classic scabland topography where some of the greatest opponents of the original flood hypothesis, upon seeing the landscape for the first time, finally admitted that J Harlan Bretz, who conceived of the idea, was right. That afternoon was spent heading back west, meeting up with the Columbia River at Wallula Gap. At the time of the floods, the river level was some 1000 feet above the group's heads at this site. After touring, the group perched on the terrace of Maryhill Estate Winery overlooking the Columbia River below. Dinner that night was at Windseeker Restaurant in The Dalles, where a huge buffet of salmon and prime rib was enjoyed.

The morning of the last day of the trip, on August 19, was spent at the Columbia Gorge Discovery Center in The Dalles, which has outstanding exhibits of the geology and local history of the area. Then it was time for the group to split up, with some having to head to Portland airport for early afternoon flights while another party still were able to take in some of the sites of the Columbia River Gorge.

Participants on the trip were Ken and Donna Barrow, Luca Bratsi, Doug Brusa, Peter and Jorie Clark, Anita Grunder, Buddy and Betsy Haas, John and Sherry Moran, George and Danielle Sharp, Joe and Karina Stoner, and Denny and Sue Tower.

Alumni in Montana

CEOAS alumni followed the route of the Ice-Age Missoula floods from their source in Montana to near their final destination in Portland, in their five-day fi eld trip in August of 2012. Photo courtesy of Peter Clark.

Alumni dinner

After a day spent looking at the record of glacial Lake Missoula, the 2012 Alumni Field Trip ended the day for dinner in Sandpoint, Idaho, where the ice dam had blocked to Clark Fork River to form the lake. Photo courtesy of Peter Clark.

Missoula floods map

Map showing the extent of the Missoula Floods in the Pacific Northwest. The blue area indicates the Cordilleran Ice Sheet. Yellow indicates the maximum extent of Glacial Lake Missoula (eastern) and Glacial Lake Columbia (western). Tan shows the areas swept by Missoula and Columbia Floods. Courtesy of USGS.

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