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 outgassing, formed a dense (< 2 % porosity), highly crystalline plug. This plug had a very low matrix permeability (10-17 to 10-18 m 2) and high tensile strength (9 to 13 MPa), forming an efficient rigid seal and preventing significant outgassing from the conduit. 2) Just below the plug, a high porosity zone (up to 50%) formed, acting as a gas storage zone, with pressurisation occurring partly under closed-system degassing. 3) The shallow conduit became pressurised due to the combination of both gas accumulation and the resistance of the plug to magma column extrusion in response to a new influx of magma. 4) On the 14 th of July a critical gas over-pressure was reached, overcoming the strength of the dense plug of magma, trigging extreme decompression and evacuation of the top two kilometres of the conduit. 5) The newly intruded magma was not directly involved in the explosion and continued to ascend during the week following the explosion.

Rheological change and degassing during a trachytic Vulcanian eruption at Kilian Volcano, Chaîne des Puys, France

“…We note that the crystallinity profiles for experiments presented in Fig. 11 are also influenced by additional parameters such as variable temperatures, dwelling time at final pressure, and the experimental procedure to reach this final pressure (singlestep vs. continuous decompression; Gaunt et al 2020). However, the decompression rate appears to be a major control of the near-surficial crystallinity range attained.…”

Petrologic monitoring at Volcán de Fuego, Guatemala

“…Gas accumulation beneath a low permeability plug in the upper conduit is also invoked to explain the high intensity of the Vulcanian eruptions common in volcanoes typified by hydrous magmas of intermediate to silicic compositions. Plug failure and subsequent downward propagation of a decompression wave rapidly ejects magma from a vertical section of the conduit (e.g., Alidibirov and Dingwell, 1996;Diller et al, 2006;Druitt et al, 2002;Gaunt et al, 2020;Wright et al, 2007). The result is a wide range of pyroclast crystallinity, vesicularity and occasionally clast morphology (e.g., Sakurajima, Tungurahua, Battaglia et al, 2019).…”

Evidence for deep gas loss in open volcanic systems

“…They are from a Vulcanian explosion on February 11, 2010 at Soufrière Hills volcano, Montserrat (Burgisser et al 2019), an explosive event on October 26, 2010 at Merapi volcano, Indonesia (Drignon et al 2016), and a large Vulcanian event that occurred on July 14, 2013 at Tungurahua volcano, Ecuador (Gaunt et al 2020). We show that the magmas feeding these Vulcanian events were crystal-rich enough to promote highly efficient outgassing by channelling.…”