QUALITATIVE CHAOS IN GEOMORPHIC SYSTEMS, WITH AN EXAMPLE FROM WETLAND RESPONSE TO SEA-LEVEL RISE

The spatial and temporal complexity of earth surface processes and landforms and the presence of deterministic chaos in many fundamental physical processes provide reasons to suspect chaos in geomorphic systems. A method is presented to assess the likelihood of chaotic behavior in a geomorphic system. The method requires identification of the fundamental system components, their positive, negative, or negligible influences on each other, and the relative strength or magnitudes of these links. Based on this information, the method can classify geomorphic systems as stable and nonchaotic, unstable and potentially chaotic, or unstable and generally chaotic. Positive, self-enhancing feedback is a key diagnostic of the likelihood of chaotic behavior. A sample application of the method to the problem of coastal marsh response to sea level rise is provided, which shows the marsh to be unstable. If changes in vegetation cover are partly dependent on vegetation density, the system is generally chaotic if marsh vegetation exhibits self-enhancing feedback (for example, seed source effects) and potentially chaotic if vegetation exhibits self-limiting feedback (competitive effects). The attractors controlling the chaotic dynamics represent states of pronounced erosion/drowning or accretion/expansion.