Sedimentologic analyses of deposits of a historic landslide dam failure in Barrancas valley causing the catastrophic 1914 Rio Colorado flood, northern Patagonia, Argentina

摘要

Most landslide dams fail shortly after their formation, however they can also persist several hundreds to thousands of years and never fail catastrophically. The interpretation of the type of failure of paleo-landslide dams bases only on sediments downstream the dam. Here we describe the matrix of sediments in Barrancas river downstream a dam which failed catastrophically in 1914. This description will help to reconstruct the process of failure of paleo-landslide dams elsewhere. Most striking feature of the outburst flood deposit is mineralogic due to the similarity of its composition with the landslide dam contrasting with the normal river sediments. Grain roundness of the outburst flood deposit is poor and increases only with erosion of substrate material from Barrancas valley several tens of km downstream the failed dam. The low fraction of clay and silt within the matrix of the outburst flood deposit ( > 3.5%) indicates the high energy of this event.