Coastal instability associated to gravitational processes in the large patagonian lakes: a study of recent events

Abstract

Subaqueous mass wasting involving coastal areas of large patagonian lakes is a little known and almost unexplored phenomenon. However, its impacts over people and coastal infrastructure are increasingly reported. In order to characterize these processes and identify their conditioning and triggering factors, we selected four sites at different lakes (Nahuel Huapi, Huechulafquen, Lacar and Espejo) where recent events took place. Available information related to these events was collected through interviews with witnesses, municipal government officials, national parks staff, owners and concessionaires of coastal areas in Parque Nacional Nahuel Huapi and Parque Nacional Lanín. The lake floor was surveyed using geophysical and photogrametric equipment (georadar, side scan sonar, phase-measuring bathymetric sounder, sub-bottom profiler, dual-frequency echosounder and drone). Satellite imagery was visually interpreted.  Morphological features suggest the occurrence of rotational mass-movements initiated at coastal sublacustrine slopes (18° - 32°) and evolving into traslational movements or channelized flows. From sedimentological and morphological analysis of the affected sites we conclude that coastal areas with high sedimentation rates show higher susceptibility, especially those with recent anthropic intervention on the subaqueous slopes. Regional or local seismic events are the most probable triggers.