This is a land of abandoned erosional waterways, streamless coulees with empty cataract cliffs and plunge basins, potholes and deep rock basins, all eroded into the basalt of the gently southwestward dipping slope of the Columbia Plateau. The pattern of dry stream ways; a plexus, an anastomosis; totally unlike any other drainage pattern on earth. A debacle was demanded to explain this landscape, the volume of which would fill normal stream valleys to overflowing. These great floods spilled over former divides, eroding their summits to complete the new network.
Associated with the enormously enlarged drainage ways were similarly huge mounds of stream gravel; great river bars. Huge stream-rolled boulders occurred in these bars. The boulders were obviously plucked from the columnar basalt bedrock by the high-velocity currents. The term valley would not suffice for the abandoned rock-bound former waterways; channels, and the entire composite; the "Channeled Scabland."
The total area involved was 18 townships wide by 22 townships long (approximately 15,500 sq miles). This seems to call for a return to "Catastrophism", a discredited theory harkening to Noah's flood. But this was no such flood and was never caused by a month of rain. This flood, or rather series of floods can be traced all the way to the Willamette Valley, south of Portland, Oregon, wherein is found a river delta of 200 square miles. Caused by the bursting of ice dams across what is now the Clark Fork of the Columbia River system in the Idaho panhandle. A lake of 3,000 square miles containing 500 cubic miles of water, half the volume of Lake Michigan. The dams are thought to have been 2,000 feet high.
The Channeled Scabland
A Guide to the Geomorphology of the Columbia Basin, Washington
Prepared for the Comparative Planetary Geology Field Conference held in the Columbia Basin
June 5-8, 1978
edited by
VICTOR R. BAKER
Department of Geological Sciences
The University of Texas at Austin
Austin, Texas 78712
and
DAG NUMMEDAL
Department of Geology
The University of South Carolina
Columbia, S. C. 29208