Thursday, July 7, 2011
A Convergence of Wonders: Day 6, In the Land of the Great Draining
The young man was stalking an elk along the shore of the huge lake where he had lived for much of his short life. Stepping quietly through the underbrush, he was sweating, not from the heat, but from exertion. There was no heat, even now in the height of summer. The ice lands lay just a few miles to the north, and the scattered low shrubs provided little shelter from the winds pouring off the frigid glacial slopes. He had been stooping for hours, staying out of sight of the animal. He carried no bow, no atlatl, for his culture knew nothing of these things. His weapon was a spear.
He was nearly close enough, and positioned himself for the attack. The elk looked up, startled, but the man had done nothing to reveal himself. The animal started bounding up the slope, and the man started running, hoping for a lucky throw, but he stopped, for now he heard what startled the animal. The ground was rumbling. The lake, he realized, was moving, and currents of muddy water were starting to tear at the banks. He watched, stunned, as the lake level started to drop. From his vantage point on the high ridge, he could see water surging through the gap in the hills, tearing away at the soil and rock. He could hear giant boulders bouncing in the depths.
In the next four days, the lake that he and his people had known for all of their lives simply disappeared. In its place were stinking mud-filled canyons and strange forests of dead trees and stumps that had been hidden by the lake's dark waters.
The elders had spoken of times like these, when the gods removed the lake as punishment for their indiscretions. The young man had no reason to disbelieve the stories, but neither had he ever thought that he would live to see the punishments carried out. His people prepared to migrate south in hopes of better hunting...
Before my archaeologist friends jump all over me, I can state that my story of people in Montana 15,000-20,000 years ago is based in no way on known archaeological data. It's just that I have read the story of the Spokane Floods from the point of view of imaginary witnesses downstream, but not from people who could have been living at the source of the great floods.
The story of J Harlan Bretz and the Spokane Floods is one of the legends of the geological sciences. Bretz had amassed a great deal of evidence supporting his contention that vast amounts of water had swept across Washington in a series of massive floods, but he could not pinpoint a source of the waters. Joseph Pardee, a U.S. Geological Survey scientist could. He had been studying odd terraces on the hills above Missoula Montana, and eventually outlined the boundaries of a huge lake in western Montana that had been hundreds of feet deep, with enough water to fill one of the Great Lakes. It was formed by a glacier that had blocked the westward drainage of the lake near Lake Pend Oreille in Idaho. The floods had come when the unstable dams had collapsed, sending cubic miles of water surging over the Columbia Plateau in Washington.
It was day 6 of our Pacific Northwest expedition, and after exploring the effects of the flood in Washington the previous day, we were having a look at the evidence for the presence of glacial Lake Missoula. Our day would end with our arrival at Glacier National Park.
We didn't stop there, but we couldn't help but pull off the highway and drive through the business district of Wallace, Idaho (below). If that elevated freeway looks somehow familiar, you have seen the movie Dante's Peak. Wallace was the stand-in for the town that was destroyed by the giant volcanic eruption while Pierce Brosnan ran around saving Linda Hamilton, and watching irritating grandma die in the acid lake. We looked and looked, but there just wasn't a huge volcano looming over the town...
The freeway is elevated because town residents fought to keep their historical district from being bulldozed for the highway. There isn't a lot of room in these narrow canyons. The towns grew along with logging and mining (this is a big silver and lead mining district), and there wasn't a lot of level ground to work with.
USGS page for a good shot), but we had a pretty good angle from near the top of Markle Pass. These ridges are ripple marks! Just like the kind you can see in the silt of any river. Of course, in a river the ripples may be an inch high, and on the Camas Prairie, the ripples are 30-35 feet high. How? In short, the ripple size is determined in large part by velocity. Water was moving over the surface of this prairie at speeds of 50-60 mph, in water that was hundreds of feet deep! It is astounding to stand at the crest of Markle Pass and imagine the scene during the collapse of the ice dam...