CLIMATE FEEDBACKS AND CRITICAL WEDGE OROGENS

A number of recent papers have demonstrated that in an idealized setting of a critical wedge orogen where fluvial erosion dominates there exists a robust scaling relationship between the accretionary flux, the average precipitation rate and the width of the wedge. This scaling relationship provides a useful measure of the relative sensitivity of wedge size and rock uplift rate to the tectonic and climatic forcing. In reality of course, the presence of the mountain alters the climate in which it finds itself. A primary mechanism through which this happens is orographic precipitation. We present a modification of the scaling relationship to include the effect that precipitation changes with the size of the critical wedge. If precipitation increases as the wedge grows, the feedback is negative. If precipitation decreases due to drying of the atmosphere with increasing average elevation, the feedback is positive. The strength of this feedback can be readily expressed in terms of the windward and leeward precipitation rates, the magnitude of the accretionary flux, the wedge geometry, and the percentage of sediment recycling. We evaluate the magnitude of these feedbacks for two recently proposed models of orographic precipitation. Under a realistic range of values, the feedback results in anywhere between a halving and a doubling of orogen width depending on the climatic and tectonic setting. Although the model framework is very idealized, it can be shown that the lessons drawn from it extend to any active orogenic belts with a tendency to evolve self-similarly.