The Post-glacial landslides in the Central Subtropical Andes of Argentina (30º S).

JEANNERET, P.; MOREIRAS S.M.; MERCHEL S.; ORGEIRA J.; AUMARTRE G.; BOURLES D.; KEDDADOUCHE K.

Simposio; Virtual DEUQUA. German Quaternary Association.; 2021

German Quaternary Association.

Glacial landscapes in active tectonic environments had been proven to be subject of the paraglacial effect around the world, recording landslides and massive rock slope failures immediately or some time after the deglaciation. Nevertheless, very few studies have been performed in the Central Andes of Argentina (31-35ºS), which has the higher peaks of South America (Aconcagua Mout 6,958 m) and was heavily glaciated during the Pleistocene. The active tectonic environment adds extra difficulty in assuming the pre-conditioning and triggering factors as the seismic forcings are coupled with the climatic forcings. This is the reason why establishing the timing of such events helps elucidating the intrinsic and external mechanisms of the landslides in order to assess the hazard in high mountain environments affected by past glaciations.Age determination in such environments are extremely difficult as they are highly dynamic and few techniques are suitable, such as the exposure ages which takes into account several correction factors associated with the altitude, snow cover and topography shielding. On this note, there are no exposure ages on any landslide or slope failure recorded around the Mercedario Peak (6?m), in the Subtropical Andes of the San Juan province, Argentina, until now. Three landslides in the Rio Blanco basin were dated with cosmogenic 10Be and 26Al, representing the first exposure ages from surficial boulders on landslides recorded in the area. After a detailed geomorphological and chronostratigraphical study, these landslides were dated in 20.9 ± 1.4, 10.8 ± 0.7 and 12.8 ± 0.9 ka, being the older one the stratigraphically lower deposit. These ages are a first approach to link the deglaciation process to a readjustment of the slopes via large landslide events.