Grandes colapsos holocénicos en el Parque Provincial Aconcagua, Mendoza.

MOREIRAS S.M.

Malargüe

Encuentro; E-ICES 7. Séptimo Encuentro Internacional Center For Earth Sciences; 2011

Landslides are major processes in the Aconcagua Park; nonetheless, this kind of events has been rarely reported as a consequence their hazard has being underestimated in the management of this natural reserve (Moreiras et al., 2008). Still rockfalls and debris flows are frequent at present, giant rotational slides moving extraordinary quantity of debris material occurred in the past. Based on stratigraphic relations with Pleistocene moraines, a Holocene age is established for these deposits. They are located above 3,200 m asl. without any evidence of being eroded by Pleistocene glacier masses. Blocks measured on the surface of the Horcones deposit resulted 11,110±760 years and 8,170±1220 years (Fauqué et al. 2009). The last catastrophic event dammed the Cuevas River valley generating an impounded lake with radiocarbon age of 11 ka (Espizúa, 1993) and cosmogenic age of 14.8±14 ka (Fauqué et al. 2009). Likewise, cosmogenic datings of rupture planes generated on the western hillslope of the Tolosa peak gave 14,650±1,900 and 11,380±1,500 years, respectively, which matches with ages measured on block surfaces of 15.5±2.1 ka and 13.9±2.1 ka (Rosas et al., 2008). Even though a seismic triggering mechanism is proposed for the dated rock avalanches, giant rotational slides identified in the Vacas River seem to be more related to debuttressing effect combined with land isostatic rebounding after Pleistocene glacier mass retreat. Maybe greater permafrost degradation and thawing during the Holocene forced slope instability in the Central Andes as well. Following this idea, Wilson et al. (2008) proposed climate as the main conditioning factor of catastrophic geological processes in Las Cuevas valley. Hence, this study advertises about the natural hazard of Aconcagua Park with an increasing tourism demands denoting the necessity of its zonation. Geomorphological parameters reveal that 89% of these events are active with very likely future reactivations amazing park activities.