Geology Reference
In-Depth Information
Downstream, the Santiam Kalapuya people of the southern Willamette Valley, Oregon, had
a story of a time the valley filled with water, forcing all the people to flee up a mountain-
side west of Corvallis before the waters receded.
One problem with attributing such stories to the Lake Missoula floods has been that the
floods occurred before the generally accepted time of human arrival in North America.
However, the recent discovery of human coprolites (fossilized excrement) radiocarbon
dated to 14,000 to 14,270 years ago at Paisley Caves, in south-central Oregon, places hu-
man populations in the region during the time of the Missoula Floods. If the region's flood
stories do record the Missoula Flood and backwater flooding of the Willamette Valley, then
it means that science is only now catching up with folklore.
In North America, glacial dam failures were not restricted to the Pacific Northwest. Cata-
strophic drainage of glacial Lake Agassiz, a vast lake that formed in a moatlike depression
on the edge of the retreating Canadian ice sheet, happened numerous times as the lake's
shoreline kept shifting as the ice melted off. Exposure of new outlets sent great floods cas-
cading off in different directions, south to the Mississippi, north through Hudson's Bay, and
east down the St. Lawrence River to the Atlantic. When the lake finally emptied for the
last time more than eight thousand years ago, it was still a hundred times larger than Lake
Missoula, releasing a pulse of freshwater big enough to change ocean circulation and shut
down the current of the Gulf Stream, which brings warm water to the North Atlantic and
keeps northern Europe habitable (without it Britain would have a climate like Siberia's).
It's no coincidence that cold periods recorded in Greenland ice cores correspond to major
drainage events from Lake Agassiz.
Given that the ancestors of Native Americans from Alaska to Tierra del Fuego are
thought to have come from Asia via the Bering Strait (whether overland or by paddling
along the coast), they would have passed near the ice sheet margin. The Native American
Clovis culture overlaps with the great outburst floods in the Midwest and Northeast that
continued to occur until glacial Lake Agassiz drained for the last time around 8,400 years
ago. Algonquin flood stories center around the Great Lakes region, along the shifting out-
lets of ice-dammed Lake Agassiz. Downstream, in Nebraska and Kansas, Pawnee stories
associate the bones of giant bison with catastrophic floods along the Missouri River. Do
