Romina Daga

Source identification of volcanic ashes by geochemical analysis of well preserved lacustrine tephras in Nahuel Huapi National Park.

Well preserved volcanic ashes produced in recent events, recovered from sedimentary sequences extracted from three lakes belonging to Nahuel Huapi National Park, Northern Patagonia, were geochemically characterized in order to reveal patterns that allow the identification of the source. Two water bodies are situated in the direct impact area of volcanoes Calbuco and Puyehue-Cordón Caulle, while the third, lake Moreno, is situated in-between. The sedimentary sequences were dated by (210)Pb and (137)Cs techniques; the elemental composition was determined by Instrumental Neutron Activation Analysis. Distinctive patterns were found out when comparing glass shards, and also white pumice but in a lesser degree, of tephra layers extracted from lake Ilón, related mostly to volcano Calbuco events, and lake Nahuel Huapi (Brazo Rincón site), associated to Puyehue-Cordón Caulle eruptions. The geochemical parameters that showed decisive differences were SiO(2) and Na(2)O+K(2)O contents, the Eu anomaly, Rare Earth element ratios; the concentration of incompatible elements Cs, Rb, Th, Hf, Ta and Zr, and the compatible elements Cr and V. The six upper tephra layers extracted from lake Moreno showed geochemical patterns that allowed clear association with Calbuco and Puyehue-Cordón Caulle sources. These results set up the base for tephrochronological applications in historical periods in Nahuel Huapi National Park area.

The crater lake of Copahue volcano (Argentina): geochemical and thermal changes between 1995 and 2015

Abstract The crater lake and associated hydrothermal features of Copahue volcano have been studied intensively over the last 20 years (1995–2015). The geochemical and isotopic compositions of the waters provide insights into the processes occurring in the volcanic–hydrothermal system, the crater lake and the thermal springs. Variations in the temperature and chemical composition of the waters reveal fundamental changes in the system that precede and accompany the magmatic and phreatic eruptive events at Copahue. A conceptual model of the summit system was developed involving the intrusion of slivers of magma in the hot acidic hydrothermal cell, the saturation of waters with secondary minerals leading to reduced permeability, the blocking of fluid pathways by liquid sulphur during heating events and the transport of gas from the magma through the ductile–brittle transition into the hydrothermal system. Geophysical data were integrated with the chemical data to provide new insights into the behaviour of the deep magmatic system that feeds the volcano edifice. Multidisciplinary studies were used to identify precursory signals of eruptive activity to give an early warning of pending volcanic hazards. Several geochemical ratios in river water were identified as potential indicators of upcoming volcanic activity, which could be used in co-operation with the community and local authorities to deal with these volcanic hazards.

Historical records of mercury in southern latitudes over 1600 years: Lake Futalaufquen, Northern Patagonia.

Mercury is released to the environment from natural and anthropogenic sources, and through atmospheric transport is distributed globally. Lake Futalaufquen (42.8°S) is an oligotrophic lake located in Los Alerces National Park (Northern Patagonia), providing a remote and unpolluted study system. A lacustrine sedimentary sequence revealed 1600 years of Hg deposition, identifying natural baselines and marked peaks not correlated with long-range atmospheric transport. Organic matter and catchment erosion were discarded as Hg drivers. Natural background, pre-1300 CE Hg concentrations, ranged between 27 and 47 ng g(-1) (accumulation rates from 8 to 15μg m(-2) y(-1)). From 1300 CE on, the Hg background profile did not follow the generally increasing Hg pattern observed in both Southern and Northern Hemisphere since pre-industrial times. It was not until the last century that a 1.6-fold increase is observed in the Hg accumulation rate, considered among the lowest increments in southern South America. Noteworthy local/regional sources of Hg for this area, along with global transport, are forest fires and volcanic activity. Between approx. 1340 and 1510 CE, sharp increase in Hg concentration and accumulation rate (up to 204 ng g(-1) and 51 μg m(-2) y(-1), respectively) were clearly associated with extended fire episodes. Furthermore, high Hg peaks during the last 300 years were associated with volcanic eruptions in northernmost Patagonia together with fairly irregular fire episodes, caused by anthropogenic burning by settling population in the Andes.