Triggering of the powerful 14 July 2013 Vulcanian explosion at Tungurahua Volcano, Ecuador

Abstract The 14 July 2013 Vulcanian explosion at Tungurahua occurred after two months of quiescence and was extremely powerful, generating some of the highest infrasound energies recorded worldwide. Here we report on how a combination of geophysical data, textural measurements, and physical and mechanical tests on eruptive products allowed us to determine the processes that led to the pressurization of the conduit and triggering of this large Vulcanian event. Two weeks prior to the 14 July event, daily seismic counts and radial tilt began to steadily increase, indicating the probable intrusion of a new batch of magma into the edifice. The 14 July explosion produced three different juvenile products that were each sampled for this study: airfall; juvenile, vesicular, pyroclastic density current material; and dense plug rocks in the form of ballistic ejecta. Feldspar microlite textures and vesicle size distributions were measured, and used jointly with a two-step recompression model to characterize the spatial distribution of gas in the conduit and the decompression histories of the erupted samples. Model results reveal a vertically stratified conduit with regards to porosity, crystallinity and volatile content prior to the explosion. Overall, our data suggests a complex sequence of events that led eventually to this powerful explosion. 1) Remnants of magma from the previous eruptive phase in May stalled in the shallow conduit, triggering crystallization which, coupled with efficient outgassing, formed a dense (