Geology Reference
In-Depth Information
ate floods as the ice dam formed, failed, and reformed every few decades from 15,300 to
12,700 years ago.
In a way, the finding that Lake Missoula failed scores of times brought Bretz's heretical
idea back into line with uniformitarian thinking. Glacial dam failure is a simple process to
understand. It works via the mechanics of floating an ice dam. Fill up a glacially dammed
lake enough to float the dam and, presto, you get an instant catastrophe. Keep filling it up
and you get a repeating series of catastrophes.
Recognition of the Missoula Floods helped identify similar landforms in Asia, Europe,
Alaska, and the American Midwest, as well as on Mars. There is now compelling evidence
for many gigantic ancient floods where glacial ice dams failed time and again on the mar-
gins of great ice sheets. In hindsight, it's obvious that ice dams are not all that intelligently
designed for the simplest of reasons—they float.
At the end of the last glaciation, giant ice-dammed lakes along glacial margins in Eurasia
and North America repeatedly produced catastrophic outburst floods. Ice dammed north-
flowing Siberian rivers, spilling them over drainage divides and changing their courses.
England's destiny as an island was sealed by erosion from glacial outburst floods that
carved the English Channel. Devastating floods were a fact of life on the margins of the
world's great ice sheets.
We now know that large ice dam failures were common in pre-historic North America
and Eurasia. And since ice dams tend to fail catastrophically, people living around ice sheet
margins probably witnessed giant floods. Could survivors of such events have passed their
stories down through the ages?
A campsite with charred bones and stone artifacts buried under pre-flood deposits
along with a stone artifact recovered from a giant flood-deposited gravel bar along the
Columbia River provide the only reported physical evidence I could find that anyone could
have witnessed a thousand-foot-high wall of water crashing through the Columbia River
gorge—and no indication of whether or not any possible human witness lived to tell about
it. Early missionaries in eastern Washington reported that Yakama and Spokane Indians
had oral traditions of a great flood that described locations where survivors sought refuge.
The native inhabitants of the lower Columbia River also reportedly had a legend of a cata-
strophic flood. Upstream in Idaho, the Nez Perce and Shoshone also had flood stories.
