The twin catastrophic flows occurred in 2014 at Ambato Range (28°09′–28°20′S), Catamarca Province, Northwest Argentina

Abstract

Two destructive and almost simultaneous flows occurred in January 2014 in Catamarca Province, Northwest Argentina. They took place in the Ambato and Siján river watersheds where the villages El Rodeo and Siján are located respectively. As a result, 15 people lost their lives, almost 100 houses and buildings were destroyed and bridges collapsed. In this paper, a comprehensive assessment of the flow events is done by the study of triggering conditions, basin morphometric parameters, flow deposits description and runout characteristics. To achieve this goal, field data, satellite image analysis, digital elevation model information and empirical equations are used. The data analysis suggests that two distinct process types acted in the Ambato and Siján watersheds. The flow event of the Ambato river basin was a debris flood characterized by an extremely high velocity (5.6 m/s) with a peak flow of 581 m3/s. The debris flood was generated by abundant sediment influx coming from landslides generated by the storm in different sub-basins and by the break of a small landslide-dam. In the case of the Siján river basin the event was a debris flow characterized by a velocity that ranged between 2 m/s to 4 m/s with a peak flow of 472 m3/s. The event was generated by an important input of sediments from hillslopes debris flows and translational slides generated during the storm that coalesced downstream forming one large debris flow. Morphometric differences between the two basins under study influenced the type and mechanism of the flows registered. The catastrophic consequences of the events highlight the necessity of an early warning system based on rainfall thresholds and hydrogeomorphic response of the basins.