Recent tectonic activity along the Bucaramanga Fault System (Chicamocha River Canyon, Eastern Cordillera of Colombia): a geomorphological approach

Tectonic geomorphology and geomorphic indices are nowadays one of the most used tools to quantify landscape response to recent tectonic activity and thus to study active faulting in orogens around the world. Based on this, a tectonic geomorphology study was conducted on the Bucaramanga Fault System (BFS) at the Chicamocha Canyon, which is structurally controlled by the Bucaramanga fault along a 36 km long section. The Chicamocha Canyon is one of the most striking landforms in the Colombian Andes, and its local environmental conditions, i.e., semi-arid climate and poorly vegetated slopes make it an outstanding laboratory to study Earth surface processes avoiding typical humid conditions. In this work, several geomorphic indices like the Hypsometric Integral (HI), the Asymmetry Factor (AF), the Ratio of Valley Floor to Valley Height (Vf), the Drainage Basin Shape index (Bs), and the Normalized Concavity Steepness (ksn) in 27 drainage basins of the Chicamocha Basin as well as channel width and slope measurements along the Chicamocha River are presented. From these indices, it was observed that drainage basins on the upthrown fault block of the Bucaramanga Fault, especially those located in southern segments between Cepita and Ricaurte, show recent tectonic surface uplift characterized by high HI, low Vf, and high ksn values. Tectonic-induced rejuvenation in some drainage basins like the Perchiquez, Guaca and Negro rivers, formed several geomorphic features such as deep V-shaped valleys, deflected drainages, barbed drainages and a regional tilting towards the NW. Besides this, threshold hillslopes reached after tectonic uplift in some drainage basins are expressed by intense landsliding in the form of debris and rock-slides, debris avalanches and debris flows, which in turn have modified the landscape of the Chicamocha canyon. Geomorphic indices obtained on the western block of the BFS hint at relatively low tectonic activity, even so recent surface uplift within three drainage basins in the San Miguel area seems to be associated with a Riedel-type structure of the Bucaramanga Fault. This work proposes a fault segmentation of the Bucaramanga Fault along the Chicamocha canyon, thus providing new evidence for the recent tectonic activity of this fault system.