Chemical water quality studies in the Central Patagonian Region of Chile following the eruption of Volcan Hudson

Abstract

In February/March, 1993, a range of water-quality variables were measured in nine freshwater lakes at different locations in Region XI, Chile . Seven of the lakes, situated between the Rio Ibanez (46°08'S) and Lago Lapparent (46 ° 14'S), are characterised by low concentrations of minerals and nutrients, similar to the oligotrophic lakes of the Araucanian district of Chile (39 °S to 42 °S) .Sulphate concentrations were disproportionately high at each of these sites and it is proposed that this results from the deposition of volcanic ash following the eruption of Volcan Hudson in August, 1991 . The concentration of sulphate found in a ninth lake well to the north of the ash deposition zone was 35 fold lower than those typically measured within the main study area.Lago Lapparent is a large `blue' lake receiving glacial sediments, that forms the southern boundary of the area studied . Concentrations of minerals and nutrients found at this site were generally even lower than those found in the other seven lakes within the area . Organochlorine pesticides were not detected at any of the sites after solid phase extraction of 250 ml water samples .

Delayed Impact of New Volcanic Ejecta on Ground Water Quality

“…The abnormal SO 4 2 − concentrations recorded at most of the sites lasted for more than 6 years after the eruption, continuing today. This represents an extremely long duration compared to that reported for surface water in previous studies (Oskarsson 1980; Klein 1981; Weaire and Manly 1996).…”

“…Volcanic eruptions can lead to drastic changes in ground water quality. Many materials adsorbed to the surface of volcanic ejecta are highly soluble, meaning that rain or surface water flowing onto freshly deposited ash will readily leach certain materials into the environment (Witham et al 2005); indeed, changes in surface water quality associated with the effects of leachate have been reported in several areas (Oskarsson 1980; Klein 1981; Weaire and Manly 1996). Previous studies report that such changes last from several days to at least 1.5 years and that the magnitude of the effect of leachate is a function of the volume of ejecta; however, to our knowledge, there are few studies that have undertaken continuous monitoring of ground water quality.…”