INTERPRETACIóN DE LA ACTIVIDAD ERUPTIVA DEL VOLCáN NEVADO DEL HUILA (COLOMBIA), 2007 - 2009: ANáLISIS DE COMPONENTES DE MATERIALES EMITIDOS

the reactivation of the nevado del huila volcano in 2007 and subsequent activity, led to the formation of large cracks at the top, small emissions of ash and continuous emissions of mud in october-november 2008. there were also major lahars, notably those generated on april 18 2007 and on november 20 2008 in where an excess of 10 and 77 million m3 of water respectively, was repported in betania reservoir (which was substantially higher than the water that could be generated by the fusion of ice-snow due to the activity). magmatic episode led to the extrusion of coalescent domes in the sw flank of pico central in 2007 and 2008. analysis of emitted ash during the eruptive episodes are characterized by varying amounts of hydrothermal mineral such as quartz, silica, feldspar, pyrite, alunite, anhydrite, gypsum, chlorite, muscovite, smectite, kaolinite and ilmenite, while the juvenile material is few or absent. these facts and the unusual volume of water involved in the generation of lahars indicate that, except for the domes, the material emitted by the volcano nevado del huila are associated to phreatic activity due to the interaction of fluids and magmatic gases with water from shallow aquifers and possibly with a hydrothermal reservoir beneath the volcano. the results of the analysis of ash as well as sediment, water and precipitates taken from the páez river support this hypothesis.