HR: 0830h
AN: T31C-0858    [PDF]
TI: Landscape Evolution Changes Along the Western Andean Mountain Front of Peru and Northern Chile
AU: * Hoke, G D
EM: gdh7@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University Snee Hall, Ithaca, NY 14853 United States
AU: Isacks, B L
EM: bli1@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University Snee Hall, Ithaca, NY 14853 United States
AU: Jordan, T E
EM: tej1@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University Snee Hall, Ithaca, NY 14853 United States
AB: We describe the along-strike changes in geomorphology on the western Andean mountain front of Peru and northern Chile, using the newly released SRTM 90 m digital topography. Strong contrasts in drainage systems and slope distributions occur along the mountain front between Lima, Peru and Santiago, Chile in concert with major latitudinal changes in climate. The climatic gradients appear to have been approximately stable since the middle Miocene. We link morphologies observed in satellite images, topography, topographically derived slope, and river networks to along-strike variations in erosional processes occurring along the climate gradient. The areas characterized below include: 1) between $12-15\deg$S, a zone where landforms suggest the important role of local precipitation, 2) from $15-18\deg$S the landforms are indicative of no significant local precipitation but significant stream power from upland regions, 3) from $18-25\deg$S there is neither local precipitation nor appreciable stream power and 4) between $25-32\deg$S where the influence of the westerly air masses gradually increases the amount of local precipitation falling on the western mountain front. Near Lima, on the western coast of Peru, the landscape is actively eroding with high median values of slope and well-developed drainage systems. We interpret this to signify that precipitation is delivered directly on the mountain front. The western mountain front of southwestern Peru contains possibly the greatest relief on earth. There, we see a bimodal slope distribution highlighting the steep slopes of the canyon networks and the low slopes of the smooth, low relief interfluve areas. The interfluves are little eroded geomorphic surfaces suggesting that precipitation rarely falls on the mountain front and that most of the water required to cut the deep canyons are derived from snow melt on the high elevations in the northernmost Altiplano. Channel profiles of the deeper canyons in this sector show that, relative to the interfluve, the river has cut back substantially into the Altiplano. A similarly smooth mountain front landscape with deeply incised canyons exists around the Arica bend in Northern Chile. However, these canyons are much smaller in drainage area and the depth of incision is much less. The channel profiles of the largest canyons in northern Chile have the same form as the interfluve, suggesting that the rivers are downcutting into the western slope but are not cutting back into the Altiplano. Slope distributions for the northern Chile region peak at approximately 3.5 degrees, the slope of the western monocline, and then fall off quickly towards higher slopes. The smooth slopes show a lack of fluvial dissection in northern Chile, which is most likely related to prolonged long-term aridity in this sector. In the north-central part of Chile, well-developed drainage systems and high median slope distributions return as the strength of the Westerlies increase towards the south.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 8110 Continental tectonics--general (0905)
DE: 9360 South America
SC: Tectonophysics [T]
MN: 2003 Fall Meeting