Tephra characterisation of the 2013 eruption of San Miguel volcano, El Salvador

Abstract

Abstract
On December 29th, 2013, San Miguel volcano, located in the south-eastern region of El Salvador, erupted after ~40 years of inactivity. The VEI 2 eruption was multi-phased and lasted for ~2 hours. The eruption ejected approximately 106 m3 of ash across more than 20,000 km2 of El Salvador extending into Honduras. The only reported damage took place in the coffee plantations on the flanks of the volcano. This eruption was of significant importance given the safety of the coffee plantation workers. In addition, approximately 70,000 people live within a 10 km radius of the vent. The abrupt nature of this eruption is also of cause for concern; a larger eruption with as little warning would be very hazardous.
Analysis and reconstruction of the eruption is based on an assortment of video evidence, photographs, and laboratory results from field sampling. Five eruptive phases occurred during the December 29th, 2013 eruption of San Miguel, including vulcanian eruptions, a pyroclastic density current, and multiple ash plumes. The eruption was a result of reactivation and mixing of the contents of underlying magma chambers.
The purpose of this study is to aid in the understanding of this particular eruption and to expand the scientific database. Scoria, ash aggregates, and juvenile ash particles collected from the eruption were analysed for compositional and textural evidence of the nature of the eruption. Ash aggregates and lithic fragments in scoria samples provide evidence of a phreatomagmatic event. Different glass types (tachylite and sideromelane) discovered in all three types of material indicate differential magma fragmentation and movement. Different internal lithofacies of ash aggregates result from the interaction with a pyroclastic density current. A transition in tephra deposits from lithic-rich to more juvenile-rich clasts support the conclusion that the eruption transitioned from partly phreatomagmatic to magmatic.