Mass-wasting events and related morphology along a coastal portion of Nahuel Huapi lake bed (Patagonia)

BEIGT, DÉBORA; VILLAROSA, GUSTAVO; GÓMEZ, EDUARDO ALBERTO

Mendoza

Congreso; 18th International Sedimentological Congress; 2010

IAS - International Association of Sedimentologists

A bathymetric survey using a Phase Measuring Bathymetric Sonar System (“GeoSwath Bathymetry SystemPlus”, GeoAcoustic Ltd.) (CONICET-IADO) was carried out at selected coastal areas of Nahuel Huapi lake onApril 2007. The equipment records the bed morphology and sedimentology with a high (submetric) resolution upto 100m depth approximately (Gómez and Maraschin, 2006).The aim of the survey was to study the origin of thetsunami that hit the coasts of S. C. de Bariloche on 22 May 1960, destroying the pier of San Carlos harbour.Analysing bathymetric data acquired at the vicinity of the harbour, a large subaqueous landslide and recent masswastingdeposits were identified below 70- 80m water depth (Villarosa et al., 2009). Through sedimentary coreinformation and high resolution seismic profiles, the authors linked the mass-failure and consequent tsunami tothe 1960 Valdivia earthquake, suggesting that the failure was probably induced by the presence of a non-cohesivesurface (tephra layer?) that acted as a sliding surface. Based on these previous results, a hypothesis about theprobable existence of landslide-prone areas in the lake bottom was established. These areas, with steep slopesand/or materials prone to fluidization below, could be destabilized during a high magnitude earthquake, causingan extraordinary wave that would affect vulnerable coasts. The aim of this work is to present preliminary resultsof a landslide susceptibility study on costal areas of Nahuel Huapi lake, particularly at the urbanized coasts of S.C. de Bariloche, Dina Huapi and adjacent zones. Subaqueous morphology along a 9-km coast from Playa Bonitato the vicinity of Ñireco stream outlet (S. C. de Bariloche) was studied. Digital elevation models (DEMs), slopemaps, bathymetric maps and bathymetric profiles were performed. Stream outlets were located and mapped.Steep slopes, subaqueous landslides, debris flow channels and probable mass- wasting deposits were found. Thegeneral areas affected by mass-wasting events were identified and related to slope ranges. In order to verify thehypothesis about the presence of potentially unstable areas in this portion of the lake bottom, next step will becollecting sedimentary cores at selected sites to determine the characteristics of the subjacent sediments.