USING FLUVIAL GEOMORPHOLOGY TO DESCRIBE ALONG-STRIKE VARIATIONS IN QUATERNARY DEFORMATION IN THE EASTERN FOOTHILLS OF THE EASTERN CORDILLERA, COLOMBIA

The Colombian Andes, comprised of the Western, Central, and Eastern Cordilleras, is actively being deformed by the interaction between the Nazca, South American, and Caribbean plates. However, how the strain at the plate boundaries is partitioned across the Andes and into the South American plate remains unclear. Of particular interest is how the mountain belt is evolving and propagating to the east. Geodetic shortening rates and shallow seismicity in the Eastern Cordillera (EC) indicate that this area is experiencing active faulting, yet the Quaternary deformation in the EC foothills remains largely unexplored. The deformation along the foothills of the EC is remarkably preserved in the landscape and thus allows us to quantify deformation. Using digital elevation models (DEMs) we have created drainage maps and longitudinal profiles along a ~230 km portion of the EC from the town of Villavicencio north to Tame. From these, we provide the magnitude of uplift and fluvial incision relative to the local base level. Additionally, we have characterized channel steepness and concavity. Plots of channel slope vs. drainage area were created to calculate normalized steepness indices and describe erosion rates relative to uplift rates. Knickpoints in river profiles record a landscape response to increases in Quaternary uplift rates. Finally, we have compared the patterns in profile steepness and knickpoints to the underlying lithology. These data have allowed us to describe along-strike patterns of uplift and gain a better understanding of where the thrust front is advancing and where the greatest seismic hazards lie. Future work will include using Terrestrial in situ Cosmogenic Nuclide geochronology on deformed terraces along the Guaicaramo thrust fault. Dating the deformed terraces will allow us to gain a quantitative understanding of how strain is partitioned in the EC foothills.