NATURAL OSCILLATIONS IN COUPLED GEOMORPHIC SYSTEMS - AN ALTERNATIVE ORIGIN FOR CYCLIC SEDIMENTATION

Internally oscillating cycles of cutting and filling occur naturally i n many coupled geomorphic systems. As a demonstration, we have modeled stream entrenchment and backfilling where alluvial systems couple to uplifting mountain blocks. This simple model tracks bedrock stream ero sion and transport of alluvium to base level. Internal oscillations ar ise from coupling of a kinematic wave model for mountain erosion to a diffusion model for the alluvial basin. Decaying periodic cutting and filling occur on time scales of 10(5) yr; the largest magnitudes are f ound at the coupling point. Model results suggest that cyclic sediment ation may result from the tintinnabulation of single perturbations app lied to natural systems and need not record cyclic changes in climate, tectonics, or base level.