Saturday, July 28, 2012
NOVA: Mystery of the Megaflood (2005) [UR] ***
This is a fairly well done documentary that explains the theory of the formation of the Channeled Scablands of eastern Washington State. The theory, first proposed by geologist J. Harlen Bretz in 1923, is that the Scablands were formed by a megaflood, although he could not identify the source of the water. Another geologist, Joseph T. Pardee, had published an earlier paper describing an enormous body of water that had covered western Montana during the last period of glaciation, although he did not hypothesize about what had happened to the water. When geologists put the two theories together with the observed physical evidence, it became evident that the Channeled Scablands were created by the abrupt collapse twelve thousand years ago of the ice dam holding back Glacial Lake Missoula. The catastrophic failure of the ice dam released a torrent of water with an estimated flow rate of ten cubic miles per hour, nearly sixty times that of the Amazon River. This water traveled westward across Idaho, Washington and Oregon for over a week, carving the Channeled Scablands and the Columbia River Gorge, and depositing massive blocks of ice and glacial erratic rocks in Oregon's Willamette Valley, before finally emptying into the Pacific Ocean via the Columbia River.
The problem with the documentary is that there are no large-scale maps showing the location and size of Glacial Lake Missoula, the Channeled Scablands, and the path of the flood waters between the two. As a result, it's difficult to get a sense of the huge scale of the flood and its impact on the geography of the Pacific Northwest. Before viewing this documentary, I suggest that you visit the Glacial Lake Missoula website, and especially the Virtual Tour. It will make viewing the documentary a much more rewarding experience.
Labels: biography, documentary
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