Abstract Medium- to high-sinuosity, aggradational submarine channels have frequently been considered analogous to subaerial channels. However, planform evolution and resulting architecture in these submarine channels are characterized by absence of downstream migration, eventual cessation of movement, and ribbon geometries. In contrast, alluvial rivers undergo continuous downstream and lateral movement to form tabular, sheetlike bodies. A simple process model of flow structure and evolution is described for these submarine channels. Flows are predicted to be highly stratified, have significant supra-levee thicknesses, and form broad over-bank wedges of low-concentration fluid. The model, for the first time, provides a coherent set of process explanations for the primary observations of submarine channels.