POSITIVE FEEDBACK CONTROLS IN THE UPLIFT OF THE NORTHERN ANDES

In actively deforming orogens local geology, tectonics, climate and surface processes do not only interact and feedback each other, but exert a control in deformation patterns, and uplift and erosion rates in mountain belts. Determining the influence that each one of these physical parameters causes in mountain growth is a complex multivariable problem. To gain some insights into this problem we isolate one variable and look at the influence of rainfall distribution in the erosion rates for a swath profile in the Eastern Cordillera of the northern Andes. We hypothesize that the marked differences in total rainfall between both sides of an orogen cause distinctive erosion rates that drive asymmetrical uplift in this region. We show that geomorphometric indexes for present landscape document a strong difference between both flanks of the mountain range and directly correlate with the rainfall distribution for this mountain range. High precipitation rates in the east flank of the Eastern Cordillera correlate with deeply incised river valleys that cut across the tectonic grain whereas lower precipitation rates in the west flank of the Eastern Cordillera correlate with moderately incised topography and structurally-controlled river valleys. Systematic long river profiles along the east flank of the Eastern Cordillera show a two-step profile where the longer upper-valley segment shows low concavity and high steepness and the lower-valley segment presents intermediate concavity and low steepness. Systematic long river profiles along the west flank of the Eastern Cordillera show a variable number of steps along the profiles with a lower steepness and a higher concavity than that of the rivers draining the east flank. Using tectonic geomorphology techniques, we isolate and determine the influence of climate patterns in erosion and uplift processes across an orogen that presents a double-verging symmetric structural style and a relatively homogeneous rock type.