La erupción del 22 de diciembre de 2012 del volcán Copahue, Neuquén, Argentina: caracterización del ciclo eruptivo y sus productos

2 INIBIOMA - CONICET-UNComa, Bariloche. 3 CIG - CONICET-UNL, La Plata. 4 IBiGeo - CONICET-unas, Salta. 5 INREMI - CONICET-UNLP, La Plata. ABSTRACT The December 22 nd 2012 eruption of the Copahue volcano, Neuquen, Argentina: Characterization of the eruptive cycle and its products This paper describes the characteristics, nature and distribution of the products of the 12/22/2012 eruption of the Copahue volcano (Neuquen Province, Argentina). The eruptive cycle was dominated by a pulsatory behavior, with a continuous decrea- se in the released energy since the onset of the eruption in the morning of December 22, when the eruptive column reached its maximum height (1,500-2,000 m). The volcanic plume extended for almost 250 km toward the ESE of the volcano and was characterized by a mean width of 20 km in proximal areas and 35 km in distal areas. This initial pulse was accompanied by significant SO 2 emissions. A second, less intense, eruptive pulse occurred during the afternoon of December 22, leading to the development of a smaller volcanic plume. Eruption products can be classified as: i) ballistic bombs and blocks emitted from the eruptive center, and ii) fallout pyroclasts deposited directly from the volcanic plume, including large flattened juve - nile fragments of highly vesiculated scoria. The characteristics of the eruptive event lead to the accumulation of tephra up to a distance of about 40 km from the crater, distributed along a surface of about 200 km 2 to the SE of the volcano. Petrographic analysis performed on the fallout deposits showed the presence of juvenile fragments with different degrees of vesiculation and accessory fragments of hydrothermally altered subvolcanic rocks. Ballistic bombs and blocks were dispersed to a distance of 1,800-1,900 m from the eruptive center. We estimate a VEI 2 eruption intensity, with an emitted volume of about 0.005 km 3 , which rapidly declined in about 48 hours after the onset of the eruption. The initial stages of the eruption were related to the interaction of an ascending column of magma with the shallow hydrothermal system of the volcano, triggering a hydromag- matic eruption. Once the conduit was open, the progressive decompression of the system led to an eruption dominated by a pulsatory magmatic fragmentation.