Mass wasting and fluvial erosion processes in Río Los Sosas gulch, province of Tucumán, Argentina

Abstract

During summer storms in late 2000 and early 2001 several mass wasting movements and fluvial erosion episodes took place along the Río Los Sosas and caused serious damage to Provincial Road N° 307, which runs parallel to the river course. The cost of the repairs amounted to U$S 821,598, and was met by external credits. The two main environmental factors directly affecting the zone were the accumulative rainfall and the intensity of the storm. In addition, man-made alteration of the natural environment intensified the affects. Lithology and regional slopes also exerted a significant control on the type of processes observed. Thus, flows occurred mainly over outcrops of low-grade metamorphic rocks, whereas debris slides took place in previous altered materials formed by weathering of the "El Indio" tonalite. Thirty six separate events were recognized in the area; most were shallow debris slides, but debris flows were more impressive in terms of magnitude. A zone of maximum hazard zone was identified between km 23 and 38 of Provincial Road N°307 where the majority of the down-slope mass movements were recognized.