Forecasting the Eruption of an Open‐Vent Volcano Using Resonant Infrasound Tones

Abstract

Open‐vent volcanic systems with active degassing are particularly effective at producing infrasound that exhibits resonant tones controlled by the geometry of the volcano's crater. Changes in the infrasound character can thus provide constraints on a crater's lava level, which may vary dynamically in the lead‐up to an eruption. Here we show that the increasing frequency content and damping characteristics of the resonant infrasound at Volcán Villarrica (Chile) relate to lava lake position in its crater/conduit preceding its 2015 eruption. We model the acoustic response of Villarrica's crater to determine that the lake began to rise on 27 February and reached the flared upper part of Villarrica's crater before oscillating during the two days prior to the 3 March paroxysm and 1.5 km‐high lava fountain. This study demonstrates the utility of remote infrasound monitoring for future eruptions of Villarrica and other analogous open‐vent volcanoes.

Single-Station Seismo-Acoustic Monitoring of Nyiragongo's Lava Lake Activity (D.R. Congo)

“…Two further attributes are of significance with respect to the lava lake level, namely the delay time of the infrasound arrival with respect to the seismic one and the frequency content of the infrasound events (Richardson et al, 2014;Johnson et al, 2018). Unfortunately, the delay time information, which is potentially useful for measuring the level of lava in a conduit (Ripepe et al, 2002;Johnson, 2007) is particularly affected by 6 km of propagation through the atmosphere (see section Identification of Repetitive Long-Period (LP) Seismo-Acoustic Events).…”

“…A more promising means to measure lava levels is afforded by the study of the acoustic resonance of the air column above the lava lake (Johnson et al, 2018). Several acoustic resonance models have been applied to other lava lake volcanoes (e.g., Bessel horn resonator at Villarrica in Richardson et al, 2014; Helmholtz resonator at Kilauea in Fee et al, 2010), the simplest one being the cylindrical geometry, or organ pipe, that could eventually fit to the shape of Nyiragongo's lava lake.…”

Tephra From the 3 March 2015 Sustained Column Related to Explosive Lava Fountain Activity at Volcán Villarrica (Chile)

“…Since April 2012, the surface activity of Villarrica has exhibited deepening of the active lava lake which persisted at a depth of 120-130 m below the crater rim up to February 2015 (Romero et al, 2016a;Johnson et al, 2018). Unrest initiated in August 2014, when the number of long-period (LP) seismic events increased and higher SO 2 fluxes (up to 5,000 tons/day) were recorded up until a few days before the eruption (Giacomozzi et al, 2015).…”

“…For instance, blocky scoria containing two populations of sub-spherical bubbles, such as those seen during the paroxysmal eruption and then during the activity of 9 December 2015 and 13 February 2017, have previously been interpreted as coming from a waning discharge through ponded lava during increased outgassing (Parcheta et al, 2013; Figure 6A). The simultaneous eruption of scoria with Johnson et al, 2018). The rising of fresh (volatile-rich) low-density magma to the surface produces lava bursting at two small vents within the solidified crust of the lava lake.…”

“…Aerial picture of the vent by Isa Stemberga. (B) An increased supply of deep-sourced volatile-rich magma produces a slug flow within the eruptive conduit, which results in the rise of lava lake (up to 60 m depth, Johnson et al, 2018), Strombolian activity and enriched CO 2 /SO 2 degassing by 2 February (Aiuppa et al, 2017). (C) The rise of a more primitive basaltic-andesite foamy magma is associated with the beginning of lava fountaining activity and sustained eruption column.…”