The extensive zone of slides on the eastern erosion scarp of Pampa de Salamanca, Chubut

Abstract

On the eastern erosion scarp of Pampa de Salamanca (extraandean Chubut) adyacent to Atlantic Coast, an extensive area of slides is identyfied. The description was done exclusively with the study of photograms and satellital images and lacking of field control. The area is located between 45°00´S and 45°45´S, and is aproximately 70-75 km in lenght from north to south. Two types of slide movements were clearly distinguished: the ancient and the modern. The first are bigger and show degradation evidences. The second are smaller and are later local movements on sections of the ancients, such as earth flows and slumps. A provisional classification of ancients is: 1) great slumps with scarse initial morphological characteristics in the proximal side and an extensive flow distal phase; 2) multiple retrogressive slumps; and 3) coalescent slumps with small terminal earthflows. The author suppose that the argillaceous lower levels (plastic and expansive) of Chenque Formation, one section on the complex Tertiary sequence, are essential to these gravitational movements. In the ancient excesive precipitations at indetermined times (Interglacial ?, Postglacial ?), were the triggering factors. In the modern movements the basal fluvial erosion contributes with the instability of the slopes. The main scope of this paper is the description and the knowledge, not only their conspicuous morphology but also is proposed its genesis.ocurred on a regional horizontal structural landscape. Other Geomorphic units are also synthetically described.