Okanogan lobe tunnel channels and subglacial floods into Moses Coulee, Channeled Scabland, northwestern United States

Abstract

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.