The Most Cataclysmic Ice Age Floods

Climate patterns were different during Ice Ages.  The Rocky Mountain region of North America is mostly arid today, but more precipitation and lower rates of evapotranspiration led to the formation of vast lakes during cooler climate phases.  Most of these lakes gradually disappeared in non-dramatic fashion after the climate became warmer and drier.  Evaporation changed the former sites of these freshwater lakes into empty basins, salt plains, and much smaller salt lakes.  But the demise of Glacial Lake Missoula caused a spectacular flood, perhaps the largest deluge in earth’s history.

A southern lobe of the Cordilleran Ice Sheet blocked the flow of the Clark Fork River near the border of present day Idaho and Montana, creating a glacial lake as big as Lake Erie and Lake Ontario combined.  At times it was almost 2000 feet deep, though it periodically lowered and partially drained.  The ice dam itself was an astonishing 2000 feet high.  The warm climate phase that marked the end of the Ice Age beginning about 15,000 years ago melted the ice dam, and the tremendous volume of water in Lake Missoula burst across Idaho and eastern and central Washington, finally emptying through the Columbia River valley into the Pacific Ocean near the present day town of Astoria, Oregon.  This massive flood created a landscape known as the “channeled scablands.”  The geological formations that serve as evidence of this cataclysm are impressive and picturesque.

Areal Scenario Map of the Ice Age Floods - Click to View Larger Image

The largest floods in the history of North America occurred in the Pacific northwest following the end of Ice Ages.

Image result for Channeled scabland

These geological landforms were caused by post Ice Age floods.

Below is a link to many more photos of these formations.

The flood carried large boulders encased in icebergs.  These “erratics” can be found throughout the channeled scablands.  There are dry falls–350 foot tall hills under where 300 feet of Lake Missoula water formerly flowed in what were temporary waterfalls.  Huge ripple marks can be seen on Camas Prairie.  Other amazing formations are the kolk potholes where swirling eddies gouged out deep troughs.  Strandlines and lake deposits visible on the sides of mountains are evidence the dissolution of glacial lakes occurred repeatedly in this region–perhaps more than 34 times during the Pleistocene.

The scouring of these intermittent Ice Age floods eroded most of the topsoil in this region and much of the scabland is unsuitable for crops.  But there are some exceptions.  The tops of some hills were above the flood and still have enough soil for growing crops, and some soil eroded from mountains into some valleys where crops can also be grown.  But for the most part agricultural activity here is limited to livestock grazing.

Humans began colonizing North America about the same time this cataclysmic flood occurred. Any people in the path of the deluge perished.  Members of the sparse population living on the edge of the flood witnessed an unusual, awe-inspiring event, a story they likely told their children and grandchildren.  It may be the origin of ancient flood myths found in Native American lore.  Flood myths are known in cultures worldwide and probably are based on inherited memories of local floods that occurred at the end of the Ice Age when glaciers melted and sea level rose rapidly.


Smith, Larry

“Repeated Sedimentation and Expanse of Glacial Lake Missoula Sediments: A Lake Level History of Garden Gulch, Mountain, USA”

Quaternary Science Review January 2017


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6 Responses to “The Most Cataclysmic Ice Age Floods”

  1. ina puustinen-westerholm Says:

    What you have exactly..what these lands around us. Our family has several generations..that have hiked, camped, floated, and played at the deathdealing game of..boulder-hopping..on the edges of the high lands. Thanks much.

  2. Neil Barden Says:

    The Americas were peopled many, many 1000’s of years earlier than 14500BP. There are about 50 well documented sites. Monte Verde, Topper, Pendejo Cave, Pedra Furada and Bluefish Caves to name a few.

    • markgelbart Says:

      There are not 50 well documented archaeological sites in the Americas before 14,500 BP. The supposed ages of the sites you mention are disputed by lots of archeologists.

    • markgelbart Says:

      Evidence from the Topper site was debunked by the study I discussed in this blog article.

      • Neil Barden Says:

        Dear Mark, thank you for the reference to the Deter-Wolf et al, (2011) paper – Jesse Tune 2nd author. I had a quick skim through it. While it may cast some doubt on the Coats-Hines Site (although I am not convinced by the author’s arguments), it most certainly does NOT ‘debunk’ the Topper site’s extreme antiquity – >50,000BP. The simple fact is that the Topper site was never a ‘high energy stream environment’. Therefore the very primitive stone tools found at Topper could not be Geofacts. This matter is fully discussed by Al Goodyear in publications on the site. In fact in a massive (1500 page) PhD study of the lithics from the Pleistocene terrace at Topper ( Sain, Douglas Allen, “Pre Clovis at Topper (38AL23): Evaluating the Role of Human versus Natural Agency in the Formation of Lithic Deposits from a Pleistocene Terrace in the American Southeast. ” PhD diss., University of Tennessee, 2015.), found that the tools were made by early humans more than 50,000 years ago.
        On another of your blog posts you note that the body mass of mammal in the USA over the last 130,000 years has gone down from 215kg to 16kg. This is the date when the evidence of humans scavenging mastodon flesh at the Cerutti site in California appears. Coincidence? I think not! If you want my full list of well documented pre-LGM sites I can post it here for you – with references. Best Regards NeilB

      • markgelbart Says:

        You didn’t read the right paper. It’s Jesse Tune’s 2018 paper that debunks the supposed antiquity of the Topper site. Here’s a link. See page 57.

        You can list 50 sites that supposedly pre-date the LGM, but most archaeologists dispute the evidence.

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