Nothing is sweeter than a powerfully sunny Saturday in autumn. And rock-heads think that perhaps the very finest way to spend such a fall Saturday, one stolen from the relentless turn of the seasons, is looking at gravel that reveals Ice Age history.
On just such a Saturday, several friends and I recently loaded my car with cold chicken, hot coffee, and a few topographic maps. The object of our quest was the evidence of violent change authored by Mother Nature a few thousand years ago. I’ve made the trip we had before us many times – far too many to count. But each time I go, I see something new, and I’m genuinely glad to show the tangible geologic evidence to others.
There was a day we geologists were confidant natural change was always gradual. Rivers and glaciers, we figured, must always move as slowly and predictably as we see them around us today. The shape of the land’s surface – the ups and downs around you wherever you live in the U.S. – could be explained mostly by the gradual erosions of streams. The slow erosion of glaciers completed the picture in the Northern Tier states, New England, and at high elevations in the Rockies.
It was a perfectly good way of looking at the world, at least for a long time.
But the evidence of the land and gravels in the central portions of the state of Washington don’t fit into that picture.
Essentially, I happen to live next to one of the most interesting places on the planet for studying how unkind the affects of climate change were roughly 14,000 years ago. In my neck-of-the-woods, every gravel pit or river bar can show the interested observer the effects of cataclysmic change, forces that revolutionized the landscape on the scale of hundreds of miles over just a few days.
The Mother-of-All-Surface-Change, if you will, stemmed from an enormous glacial lake that existed in the late Ice Age in what’s now Montana. Called Glacial Lake Missoula, the lake held about as much water as Lake Superior. But Lake Missoula was at high elevation – in the Rockies – and it was held in place not by the Earth but by a dam in the Clark Fork Valley of Idaho that was made of glacial ice.
Obviously, ice dams are dicey. Glacial ice always advances and retreats, and ice is a tad more fragile than rock. The day came that the ice dam melted or broke – as it simply had to at some point – and all of the waters of Lake Missoula in Montana started to move downstream and toward the west.
Lake Missoula created no ordinary springtime flood, but inundated whole sections of the Northwest. At first, the water depth was measured in thousands of feet, such was the depth of the former lake. The torrent carried boulders, gravel, sand and ice, all in the waters moving downhill at the speed of a freight train.
When the waters hit my native Washington and started to spread out, they were still hundreds of feet deep. They stripped away our soil and carved down into the bedrock creating “coulees,” or flat-bottomed gashes into the Earth. To this day, the coulees crisscross what we call the Scablands, a landscape that only a native can love (but that I surely do!).
The floodwaters continued on their journey, hitting the valleys of the Snake and Columbia Rivers. The tremendous erosional power of the mega-flood helped to enlarge the Columbia River Gorge that cuts through the Cascade Mountains. Finally, the floodwaters were discharged into the sea.
Mother Nature wasn’t sweet and gentle in the late Ice Age. If you want to learn more the tangible evidence for her fiercest moods yourself, you can spend some winter evenings reading by the fire about the events just sketched. (There are both books and zillions of internet offerings on the topic, too many to list here.) Then, next summer or early fall, come to the Inland Northwest and see for yourself.
With glorious sunny days and cold chicken lunches thrown into the mix, what’s not to like?