Análisis textural de los depósitos de ceniza emitidos por el volcán Tungurahua durante las fases eruptivas de marzo y julio 2013 y su relación con el dinamismo eruptivo.

Abstract

This work presents a textural analysis of plagioclase microlites, components of volcanic ash samples, collected during the March and July 2013 eruptive phases at Tungurahua volcano. For this study, open-source softwares were used to obtain textural parameters from back-scattered electron images (BSE). These parameters and previous geochemical data were used to calculate magma ascent rates. Different eruptive dynamics influenced by crystallization, volatile contents, and magma ascent rate, were present in the March and July phases. The March eruptive phase shows an inverse correlation between magma ascent rate and plagioclase microlite abundance. The activity occurred in an open-vent system for magma outgassing. Therefore, the behaviour observed is interpreted as the result of the rise of a magma whose ascent rate is conditioned by the variation of its viscosity, which depends on the degree of degassing-induced crystallization. Ash samples collected during the July 14th vulcanian event show a direct correlation between magma ascent rate and microlite abundance. The event took place within a closed-vent system due to the formation of a dense plug prior to the eruption. This study proposes that in closed systems, the principal factor affecting the ascent rate is magma buoyancy, unlike open systems, where viscosity prevails. During the rest of the July phase, the eruptive activity returned to an open-vent system. This work shows that textural analysis of volcanic ash samples can provide insights into magmatic processes occurring within the conduit. Therefore, this method represents an effective petrological monitoring tool for active volcanoes.cd