INTERPRETATION OF 2007 - 2009 ERUPTIVE ACTIVITY OF NEVADO DELHUILA VOLCANO (COLOMBIA): COMPONENT ANALYSIS OF EMITTEDMATERIAL.

Abstract

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 excessof 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 episodeled to the extrusion of coalescent domes in the SW flank of Pico Central in 2007 and 2008. Analysis of emitte dash 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, whilethe juvenile material is few or absent. These facts and the unusual volume of water involved in the generation oflahars 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 aquifersand possibly with a hydrothermal reservoir beneath the volcano. The results of the analysis of ash as well assediment, water and precipitates taken from the Páez River support this hypothesis.

Keywords: Volcán Nevado del Huila, phreatic eruptions, ash fall, hydrothermal minerals, lahars, dome.