500 cubic miles. Cubic. Fucking. Miles.
Glacial Lake Missoula.
Imagine, then, the pressure at the base of the dam. The ice wall, seamed and fissured by pressure, by the stresses of traveling thousands of miles from the snowy field of its origin. And the water, beneath tens of millions of gallons of water above it, forcing its way into the cracks, wedging into those fissures. Fingers of water driven by incalculable mass; melting, shearing, driving deeper and deeper into the glacier. Wedging the frozen mass away from the bare rock on which it rests. Burrowing ever closer to the far side of the monster jumble of ice, snow and rock. Closer…closer…
And then, finally, a jet of water from the base of the ice dam. Another. Three more, a dozen; the first block tumbles from the bulging pile. Groaning, shrieking, the ice wall collapses, the water boiling through.
Another flood has begun.
“When Glacial Lake Missoula burst through the ice dam and exploded
downstream, it did so at a rate 10 times the combined flow of all the rivers of the world. This towering mass of water and ice literally shook the ground as it thundered towards the Pacific Ocean, stripping away thick soils and cutting deep canyons in the underlying bedrock. With flood waters roaring across the landscape at speeds approaching 65 miles per hour, the lake would have drained in as little as 48 hours.”
“From stratigraphic successions of approximately 40 rhythmic beds at exposures in Montana, Washington, and Oregon, Waitt (1980b) inferred that approximately 40 great jökulhlaups had escaped last glacial Lake Missoula. The number "40" is a minimum; there were at least that many huge floods during the last glaciation. Although problems remain on the number and correlation of events attributed in various areas to successive Missoula floods, regionally scattered sections indicate that there were more than 40 colossal last-glacial floods, probably more than 60. “
Of all the geologic acts that shaped my home here in the Pacific Northwest, perhaps the most dramatic and greatest were these: the Missoula Floods. Everywhere I go, every day, I see the work done by the last of these inundations. Even our little house, way up in North Portland, is set on the tail end of the monster pendant bar of Alameda Ridge, a pile of boulders, gravel sand and silt that settled in the calm water behind the volcano we now call Rocky Butte, the then-conical hill serving as a flowbreak and being ripped to pieces in the process.
One of the questions I was always asked by my students during our PCC geology field trips was: “Were there any people who could have actually seen the floods?” As of today no fossil remains have been found in any of the flood deposits, although we know there were many large animals living on the Columbia Plateau at the time. When Harlan Bretz’s flood theories were accepted our notion of human arrival in North America postdated the last flood by about 1,000 years. Those ideas are in the process of changing. So it is possible, and even likely, that small bands of firstcomers were abroad on the high plateau at the time.
Maybe it’s a tiny tremor in the ground beneath you. Maybe it’s a sound, a breathless hush of a sound, just below the threshold of true hearing. Maybe it’s just a feeling inside you, like the feeling you’ve learned to trust while hunting, the feeling that something has changed. You sit up, then you stand up. You stare out into the darkness, willing your eyes to see whatever it is that is pressing on you like a stone on your chest. You know, now, you know that something is out beyond the ring of firelight, something moving, something vast, something frightening, but you can’t see and don’t know what it is.
Perhaps you have time to wake your companions. Perhaps you all jump up, try to run, try to hide, dissolve into hopeless panic before the wall of water sweeps you all away into chaos and the darkness of the vanished years.
Or perhaps you can only stand there, transfixed, staring at the long white line across the black horizon, as the first cold puff of wind racing out before the waters shivers your cheek like a lover’s last caress.