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This Land Long Ago
The Glacial Lake Missoula Floods & Ancient Climate Change
Charley Pike
April 15, 2024
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Charley
Overheard last week
“If I have to keep telling you everything, how are you going to learn anything?”
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— This Week —
The Glacial Lake Missoula Floods
Where’s This Picture?
On Charley’s Mind—Public Land Access
Coming Next Week
The Glacial Lake Missoula Floods-Then and Today
As early as the 1880s geologists suggested an immense lake had once filled the mountain valleys of western Montana.
New research is suggesting the Glacial Lake Missoula floods contributed to global climate change—13,000 years ago!
Some 20,000 years ago the Pleistocene Ice Age was waning. For 2 million years ice sheets had covered much of the Northern Hemisphere. But these continental glaciers, thousands of feet thick, were beginning to retreat as global temperatures began ever so slowly increasing.
The Cordilleran Continental Ice Sheet had pushed immense fingers of ice into the deep mountain valleys of what is now northwestern Montana and north Idaho and Washington. About 15,000 years ago one of those fingers, the Purcell Lobe, slide into a trench at present-day Lake Pend Oreille in the Idaho panhandle—the 4th deepest lake in the U.S.
In the 1920s geologist J. Harlan Bretz began publishing papers suggesting a massive lake was created by the Purcell Lobe ice dam. Bretz’s papers were controversial and even ridiculed.
Bretz said a 2,000-foot-tall, 10-mile-long lobe dammed the Clark Fork River that flowed west out of Montana.
It’s now accepted that Bretz had it pegged. The Purcell Lobe caused the formation of a lake which filled the valleys of what is now western Montana. Glacial Lake Missoula covered 3,000 square miles containing 500-600 cubic miles of water—more than the combined volume of lake’s Ontario and Erie.
At Missoula, the lake’s depth reached 1,050 feet, defined by the highest “strandlines” which are still visible today on the mountainsides near the city and throughout western Montana.
Eventually the ice dam began to succumb to the tremendous pressure behind it. The glacial-till water became superheated by friction as it blasted through fissures in the ice. It’s believed that once the lobe’s erosion began, it took only hours for the dam to explode. And it took only 2-3 days for Glacial Lake Missoula to drain—a picosecond in geologic time.
And drain it did! Water blew by the dam at speeds of up to 80 mph. Peak volume was equivalent to the flow of 18 Amazon rivers. The flood waters swept west and south inundating thousands of square miles, gouging out the Grand Coulee and the Columbia Gorge along the way. At a pinch-point in the lower Columbia valley, the Kalama Gap, the floodwaters backed 100 miles up the Willamette River valley.
The floodwater hit the Pacific Ocean with enough volume and force to carry sediment hundreds of miles into the ocean.
By the 1980s geologists began discovering that there were actually a series of Glacial Lake Missoula floods. The stubborn Purcell Lobe had formed and reformed while still attached to the ice sheet. Up to 100 floods are thought to have occurred in 50-100-year intervals. The transformation of the outwash plains in Washington and Oregon is of well-documented and epic proportions.
What Does it Matter today?
“The overall trigger for the end of the last ice age came as Earth's orientation toward the sun shifted about 20,000 years ago.” — National Science Foundation
Scientists are using novel conceptual and physical modeling to study the climate impacts of the ancient Glacial Lake Missoula Floods. And emerging information about the effects of the floods is contributing to present-day climate change theories.
In reports as controversial today as J. Harlen Bretz’s 1920s Glacial Lake Missoula research, workers with the Woods Hole Oceanographic Institution suggest the Lake Missoula floods accelerated Pleistocene era climate shift.
North Pacific seawater was much saltier (and thus denser) 15,000 years ago than today—and much colder. Woods Hole scientists believe the water released from the floods changed seawater composition and altered North Pacific currents as far west as Japan and north to the Bering Sea.
Also, the last of the floods occurred during the time when the Bering Land Bridge was being inundated by rising sea levels. Models show sea currents carrying the flood waters through the Bering Strait and into the Arctic Ocean.
These periodic thermal intrusions are thought to have alternately warmed and cooled Arctic waters as far east as the Scandinavian Peninsula. That shift in water temperatures may have been enough to accelerate an already changing global climate. It’s comparable to how the undulating El Nino and La Nina Pacific current patterns impact global weather patterns today.
This research by Woods Hole and other institutions is important as scientists try to sort out the dynamics of Pleistocene era climate change and compare that information to theories about current-day climate change.
It’s interesting to note there’s no evidence that humans inhabited the region at the time of the Lake Missoula floods. Humans though were probably crossing the Bering Strait from Siberia a thousand years before, and during the floods.
Who knows but there may have been witnesses to the Glacial Lake Missoula Floods!
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On Charley’s Mind - Public Land Access
Especially in election years arguments and rhetoric surrounding the issue of public lands access cause fevers to soar and tempers to erupt. There’s hardly any middle ground. The battles wage between those who assign the sovereignty of the Public Trust Doctrine to the land, and those who believe personal property rights are fundamental to American life.
Nearly 60% of Montana is privately owned. The federal government manages about 29% and the rest is mostly held in Indian Trust and State School Trust.
Since non-Indigenous people started working their way into Montana, someone has always had a few bucks to stake a claim to a chunk of the state.
The U.S. government carved Forest Service and Bureau of Land Management lands off from areas that were roughly of less value for tillage and grazing. Most notably by homesteading, land was up for grabs. Wealthy investors competed with homesteaders in a long and sorted story of land and water battles fought in and out of Helena…
Fast-forwarding to today, the landscape is changing—figuratively and literally. More money than we ever thought possible is flooding into the state. And with money comes control, further widening the rift between those who own land and those who want access to it and through it.
But for now I’m remined of what Ted Turner once said during an invited visit to the 1993 Montana Stockgrowers Association convention in Billings. Responding to a query as to why he posted his newly-purchased Flying D Ranch to hunting and fishing—and closed off access to adjacent Forest Service land—Turner replied:
“If you want to be guaranteed a place to hunt, work hard for 40 years and buy your own goddam ranch.”
There’s a lot to think about in Turner’s comments… Over the next few months we’ll be sorting through the arguments swirling around land and water access. Stay connected— Charley Pike
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Where’s this Photo?
Here’s this week’s “mystery” photo - a Charley Pike original. Name the bridge! Email [email protected] with your guess! You can see the answer in next week’s post.
Last week’s photo was Big Horn Lake. The lake extends 70 miles into Wyoming behind the 425-foot-high Yellowtail Dam at Ft. Smith.
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Coming Next Week
Fish On! - Feature—Getting spring fever? Let’s talk more fishing!
On Charley’s Mind—Of course Charley always has opinion, analysis, commentary, or random thoughts on his mind.
Where’s This Picture?—This is a regular content in these posts and on montanacharley.com.
Book Sharing—Every so often you’ll find a review of a book about Montana.
What else?—’Thinking about it…
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Still in the Works—A feature detailing a study to re-establish the former North Coast Hiawatha passenger rail line through southern Montana.
Formulating—More on public lands access and the growing social and political controversies surrounding land and water access.
