Resumo

GONZALEZ DIAZ, Emilio F.  e  FOLGUERA, Andrés. Mass wasting in the Neuquén Cordillerasouth of 38º: its trigger factors. Rev. Asoc. Geol. Argent. [online]. 2009, vol.64, n.4, pp.569-585. ISSN 0004-4822.

The previous analysis of the prehistoricslide phenomena in the main Andes of Neuquén Province in Argentina (36º-38ºS), triggered the study of those locatedsouth of this latitude. Therefore a new set of mass wasting deposits has beenidentified, whose trigger factors and corresponding tectonic framework, wherethey are located, differ from the northern slides. Their study was performed inthree specific areas: Aluminé, Chapelco and Arroyo Limay Chico. Earth flowspredominate in relation to slumps. The only exception is the Chapelco rockavalanche. Their occurrence seems to be related to the presence of Limay Chicomember of the Caleufú Formation, whose lithology (expanding clays), particularrheology before water saturation, and particular disposition underlyingbasaltic lava and conglomeradic plains were conditioning factors. The triggerfactor of the Present and prehistoric earth flows has been intense orographicprecipitations. Water saturation reduced friction and cohesion in materials,incrementing water pore pressure and producing slope instabilities. Rotationalslides are related to the slope basal erosion produced by lateral rivermigration and additionally to precipitations. Slope orientation has beenimportant in determining location of main slides. Lateral slope release throughthe flanks of glacial valleys due to debutressing because of the glacial retirein the area, has produced instability and rock fracturation that led to slidephenomena. The Chapelco rock avalanche is particularly related to copiousprecipitations during postglacial times. Thus sliding main trigger factorssouth of 38ºS differ from those proposed for the northern area whereearthquakes dominated. Their specific age is still unknown, although theirgeomorphologic analysis allow to constraint a postglacial age for all theseoccurrences. However, temporal relationships are lacking for the specific caseof the arroyo Limay Chico, beyond the glaciated area.

Palavras-chave : Neuquén Andes; Landslide induction; Slides; Rock avalanche; Earth slopes; Slumps; Caleufú Formation.

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