HILLSLOPE AND CHANNEL EVOLUTION IN A MARINE TERRACED LANDSCAPE, SANTA-CRUZ, CALIFORNIA

A flight of marine terraces along the central California coastline provides a unique setting for the study of topographic evolution. Wavecut platforms mantled by 2-6 m of marine terrace cover deposits are separated by 10-50 m tall decaying sea cliffs. Paleocliff edges become more rounded with age, yet the details of the profiles and frequent bedrock exposure on the upper slopes imply weathering-limited transport. Five bedrock stream channels etched through the marine terrace sequence display one to three distinct convexities in their longitudinal profiles. Detailed hand level surveys of the hillslopes and of the stream channel longitudinal profiles constrain hillslope evolution and channel incision components of a numerical model of landscape evolution. We account for regolith production as a function of regolith depth. In accord with the field observation that hillslope processes are presently dominated by the activities of burrowing rodents, the transport process is taken to be diffusive. Stream incision is assumed to be controlled by stream power, for which we use the surrogate of local drainage area-slope product. Best fits of the numerical model to field data imply: hillslope diffusivity is 10 m2 kyr-1; regolith production rate on bare bedrock is 0.3 m kyr-1, and falls off rapidly with regolith cover, and the constant controlling the efficiency of stream incision is 5 to 7 x 10(-7) m-1 kyr-1.