HR: 15:25h
AN: T33E-08    [Abstracts]
TI: Climatic controls on drainage basin topography â€" a synopsis of the western Andean flanks between 15.5 S and 41.5 S lat
AU: * Rehak, K
EM: rehak@geo.uni-potsdam.de
AF: University of Potsdam, Karl-Liebknecht-Str. 24, Potsdam, 14476, Germany
AU: Strecker, M R
EM: strecker@geo.uni-potsdam.de
AF: University of Potsdam, Karl-Liebknecht-Str. 24, Potsdam, 14476, Germany
AU: Echtler, H P
EM: helle@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473, Germany
AU: Bookhagen, B
EM: bodo@pangea.stanford.edu
AF: Stanford University, Serra Mall, Stanford, CA 94305, United States
AB: Topography in tectonically active mountain ranges is determined by the interplay between tectonics and climate. Due to the complexity of natural systems it is difficult to evaluate tectonic versus climatic contributions to the long- term landscape evolution. Previous studies suggest that rainfall and its variability strongly influence the morphology of river profiles and mountain ranges. However, it is still controversially discussed how drainage basins reflect tectonic and climatic processes. The Andean Cordillera provides a unique natural setting for studying the relationship between climate, tectonics, and topography. The Andes host various climatic zones with pronounced differences in rainfall regimes. In the central to southern western Andes, climate ranges from hyperarid in the Atacama Desert, 22 to 23°S lat, with a mean annual rainfall of ~ 5 mm/yr to year-round humid conditions south of Valdivia, ~ 40°S lat, with more than 2500 mm/yr. This zonation is controlled by hemisphere-scale atmospheric circulation patterns. With the exception of a northward shift of the Southern Hemisphere Westerlies during glacials the overall precipitation pattern has remained stable on the west coast of South America. The shelf width is reasonably constant along the margin. Uplift rate and lithology vary non-systematically and do not correlate with climatic parameters. Here, we present an analysis of 120 drainage basins along the watershed of the western Andean flank between 15.5 S and 41.5 S lat, using SRTMV3-90m data and a high-resolution rainfall dataset (TRMM 5x5 km). The basins comprise drainage areas of 1 to ~ 30 x 103 km2 and were split into subsets according to position and size. For each basin, we extracted 21 geometry, relief, and climate parameters in order to unravel the determinants of drainage-basin morphology. Our data shows that river-profile concavity and slope, hypsometric integral, basin maximum and mean elevation decrease with increasing rainfall and descending snowline. Interestingly, our results document that local relief (calculated over a 4.5-km-radius) reaches a maximum of ~ 750 m in a zone between ~ 30° to 35°S lat, which is characterized by a low-frequency, high-magnitude rainfall regime in the transition between arid to semi-arid climate. During glacials this region was affected by the Westerlies and influenced by localized glacial erosion. Relief generation in this region might be enhanced by landslides, flooding events, and debris flows, which quickly dislocate and transport large amounts of material out of the higher-elevated parts of drainage basins. High local relief appears to be preserved due to the absence of continuous rainfall and associated diffusive hillslope processes, preventing sediment production, valley infill, and the coeval smoothing of interfluves. Contrasting, the southern regions between 35° to 40°S lat, receiving higher rainfall amounts, show a lower local relief of ~ 200 m. This might be controlled by a combination of more efficient erosion, sediment production, and accumulation. Our results suggests that the transition zone between 30° and 35°S lat constitutes a transient in landscape evolution which still reflects past climatic conditions. The interaction between sparse, highly episodic rainfall and long periods of aridity appears to significantly facilitate relief preservation and maybe generation. Contrasting, continuous rainfall and the dominance of fluvial processes appear to efficiently smooth relief.
DE: 1807 Climate impacts
DE: 1824 Geomorphology: general (1625)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: 2007 Fall Meeting