Recent tectonic and volcanic influence on the fluvial dynamics of the Anaime River (Cajamarca, Central Cordillera of Colombia)

Abstract

The Anaime River valley is located at the central segment of the Central Cordillera of Colombia, a zone where regional structures like the Palestina and Ibagué fault systems have a significant tectonic influence. Additionally, the study area has been affected by recent volcanic activity produced by the Cerro Machín Volcano in the past 5000 years. In this work, we present a quantitative geomorphology analysis along the Anaime River valley by using several geomorphic indexes such as the hypsometric curve, the index of drainage basin shape, the asymmetry factor, the ratio of valley floor width to valley height, normalized longitudinal stream profiles, and the relative slope-extension index. The main goal of this work is to better constraint the influence of tectonic and volcanic processes on the recent landscape evolution along the Anaime River. The geomorphological analysis carried out in this work suggests that recent landscape evolution of upper reaches of the Anaime River and some tributaries has been controlled by a base-level fall induced by recent surface uplift along the Palestina Fault and with some influence of the Ibagué Fault. The presence of multiple mobile knickpoints in some tributaries of the Anaime River can be positively correlated with interpreted lineaments of the Palestina Fault, and therefore it is hypothesized that this structure has been acting modeling both the long and the shortterm landscape evolution. On the other hand, pyroclastic events associated with the Holocene activity of the Cerro Machín Volcano have induced landscape and drainage adjustments to compensate the large volumes of pyroclastic material introduced into the Anaime River Valley. These anomalies induced by pyroclastic flows have remained in a timescale of about 102 to 103 years, and it can be observed by analyzing the hypsometric curves and normalized longitudinal profiles of some tributaries located on the lower reaches of the Anaime River.