Search

Outburst floods from glacial Lake Missoula largely explain erosion of the Channeled Scabland, a system of overfit, basaltic channels in Washington, northwestern United States. However, it is challenging to explain Missoula flood routing into Moses Coulee due to its topographic isolation from flood routes. To clarify flood pathways into Moses Coulee, we mapped channels that delineate a radial-anastomosing network connecting to Moses Coulee. Channels consist of coulee-like features eroded mainly in basalt. Channels climb adverse slopes and cross divides, and the network is draped with eskers and recessional moraines. These channel geometries and glacial landform associations suggest a tunnel channel network. Large channel dimensions and network anastomosis indicate formation in subglacial floods. The network connects to Moses Coulee with sufficient cross-sectional area to convey megafloods, hinting that subglacial floods may have been a significant source of Moses Coulee meltwater, in addition to possible diverted Missoula floods. [ABSTRACT FROM AUTHOR]

The Channeled Scabland, Washington State, United States, is only partly the result of erosion by the catastrophic drainage of Glacial Lake Missoula: there were other sources of meltwater. Recent sedimentary investigations of some sites in the Missoula basin, and in the Channeled Scabland, support a single large late Wisconsin flood, as opposed to multiple floods proposed for this time period. Sediment in the Glacial Lake Missoula basin records rapid infill by jokulhlaups draining into Lake Missoula from upstream, punctuating a long period of normal varve sedimentation. This was independent of sedimentation in the main Scabland tract, where proximal and distal rhythmic beds are explained as resulting from multiple pulses, or surges, within a single flood. Geomorphic and sedimentary evidence supports the conclusion that drainage from the Cordilleran trunk valleys was important, and pulses were probably related to the drainage of these valleys.