Effects of tributary debris on the longitudinal profile of the Colorado

river, with the rapids owing their existence primarily to tributary debris flows. The debris flows deposit subaerial debris fans that constrict the channel laterally and, when they enter the river, raise the bed elevation. The rapids are short-wavelength (0.1 to 1 km), small-amplitude ( 5 m) convexities in the river’s longitudinal profile, arising from the shallow gradient in the upstream pool and the steep gradient through the rapid itself. Analysis of the entire longitudinal profile through Grand Canyon reveals two long-wavelength (100 km), large-amplitude (15–30 m) river profile convexities: the eastern canyon convexity between river mile (RM) 30 and RM 80 and the western canyon convexity between RM 150 and RM 250. Convexities of intermediate scale are also identified in the longitudinal profile. These longer-wavelength, larger-amplitude convexities have strong spatial correlations with high rates of debris flow occurrence, high densities of Holocene debris fans, the largest debris fans along the river, and alluvial thicknesses of 10 m or more. River profile convexities are unstable and require an active and powerful geologic process to maintain them, in this case the abundant, frequent, and voluminous Holocene debris flow activity in Grand Canyon. At all wavelengths th