Erosional processes, topographic length-scales and geomorphic evolution in arid climatic environments: the ‘Lluta collapse', northern Chile

The ‘Lluta collapse' of northern Chile is one of the oldest recognizable landslides (>2.5Ma) in a hyperarid continental setting. This paper develops a conceptual landscape evolution model of the ‘Lluta collapse' and analyzes the controls of mass wasting and erosion/sediment transport in channels on the topographic development. The data presented here imply that high relief along a topographic scarp, surface fracturing, elevated groundwater table during a more humid climate and an aquitard underlying permeable ignimbrites are preparatory causal factors for landsliding >2.5Ma ago. A strong seismic event then possibly resulted in the displacement of ca. 26km3 of mass. Subsequent modification of the landslide scar occurred by backward erosion, resulting in the establishment of a dendritic drainage network and the removal of an additional ca. 24km3 of material. It appears that this mass was produced by mass wasting in the headwaters, and exported by high-concentrated debris flows in channels. In addition, morphometric information suggest that whereas the geometrical development of the ‘Lluta collapse' has been controlled by gravitational mass wasting, the rates of the development of this geomorphic unit have been limited by the export rates of mass and hence by the transport capacity of the flow