Tracking eruptive phenomena by infrasound: May 13, 2008 eruption at Mt. Etna (original) (raw)
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Monitoring Seismo-volcanic and Infrasonic Signals at Volcanoes: Mt. Etna Case Study
Pure and Applied Geophysics, 2012
Deriving eruption source parameters from geophysical data is critical for volcano hazard mitigation, yet remains a challenging task in most volcanoes worldwide. in this work, we explored the temporal relationship between geophysical signals and eruptive parameters measured during six explosive episodes from the new Southeast crater of Mt. etna (italy). the quadratic reduced seismic velocity and pressure were calculated to track the temporal variation of volcanic elastic radiation, and the lava fountain height was estimated by thermal camera image processing. the temporal relationships between these geophysical and eruptive time series were studied. In particular, the first considered lava fountain exhibited a "clockwise hysteresis" pattern: higher seismic amplitude with respect to the fountain height during the waxing phase as compared to the waning phase. We also calculated the regression parameters for both linear and power laws, linking seismo-acoustic and eruptive time series. For the linear regressions, we found fairly constant values of the scaling factors in five out of six eruptive episodes, which can be considered as a promising step to derive eruption source parameters from geophysical data in real-time. Regarding power law regressions, a clear relationship was observed between the exponents determined for the power law linking quadratic reduced velocity and lava fountain height, and the time interval duration from the previous eruption. these results suggest that the condition of the uppermost part of the plumbing system (e.g. viscosity of residing magma and conduit conditions) play a key role in the seismic energy generation during the eruptions. Effective hazard assessment and consequently risk mitigation during ash-rich explosive activities mainly rely on volcanic ash transport and dispersion models, which require as input the eruption source parameters (i.e. mass eruption rate, column height, total mass), that can change rapidly during an eruption (e.g. 1,2). However, on the basis of the current state of scientific knowledge, real-time estimation of the eruption source parameters is not feasible for most volcanoes worldwide (e.g. 1,3). Indeed, the real-time retrievals of those parameters can be carried out with remote sensing systems as radars and lidars that, however, are expensive and used at only a few volcanoes (e.g. 3-6). Seismic and infrasonic monitoring is routinely operated on many volcanoes around the world and sensors are relatively cheap. Hence, deriving eruption source parameters from real-time streaming of these geophysical data is a fascinating and challenging task that could seriously improve the monitoring of ash-rich explosive eruptions. Some studies have shown how the increase in seismic amplitudes (for instance due to volcanic tremor variations) corresponds to the intensification in magma discharge rate, column height and, consequently, to the Volcanic Explosivity Index (e.g. 7-12). Furthermore, infrasound has been used to infer mass eruption rate, plume height and volatile mass flux (e.g. 11,13-17). As summarized by Ichihara 11 who focused on eruption seismic and acoustic tremor, most of the authors have developed power-law models with seismic or acoustic squared-amplitude or energy proportional to eruption rate
Interpretation and utility of infrasonic records from erupting volcanoes
Journal of Volcanology and Geothermal Research, 2003
In the most basic seismo^acoustic studies at volcanoes, infrasound monitoring enables differentiation between sub-surface seismicity and the seismicity associated with gas release. Under optimal conditions, complicated degassing signals can be understood, relative explosion size can be assessed, and variable seismo^acoustic energy partitioning can be interpreted. The extent to which these points may be investigated depends upon the quality of the infrasonic records (a function of background wind noise, microphone sensitivity, and microphone array geometry) and the type of activity generated by the volcano (frequency of explosions, bandwidth of the signals, and coupling efficiency of the explosion to elastic energy). To illustrate the features, benefits, and limitations of infrasonic recordings at volcanoes, we showcase acoustic and seismic records from five volcanoes characterized by explosive degassing. These five volcanoes (Erebus in Antarctica, Karymsky in Russia, and Sangay, Tungurahua, and Pichincha in Ecuador) were the focus of seismo^acoustic experiments between 1997 and 2000. Each case study provides background information about the volcanic activity, an overview of visual observations during the period of monitoring, and examples of seismo^acoustic data. We discuss the benefits and utility of the infrasound study at each respective volcano. Finally, we compare the infrasound records and eruptive activity from these volcanoes with other volcanoes that have been the focus of previous seismo^acoustic experiments.
Volcanic eruptions observed with infrasound
Geophysical research letters, 2004
1] Infrasonic airwaves produced by active volcanoes provide valuable insight into the eruption dynamics. Because the infrasonic pressure field may be directly associated with the flux rate of gas released at a volcanic vent, infrasound also enhances the efficacy of volcanic hazard monitoring and continuous studies of conduit processes. Here we present new results from Erebus, Fuego, and Villarrica volcanoes highlighting uses of infrasound for constraining quantitative eruption parameters, such as eruption duration, source mechanism, and explosive gas flux.
Volcano infrasound: progress and future directions
Bulletin of Volcanology
Over the past two decades (2000–2020), volcano infrasound (acoustic waves with frequencies less than 20 Hz propagating in the atmosphere) has evolved from an area of academic research to a useful monitoring tool. As a result, infrasound is routinely used by volcano observatories around the world to detect, locate, and characterize volcanic activity. It is particularly useful in confirming subaerial activity and monitoring remote eruptions, and it has shown promise in forecasting paroxysmal activity at open-vent systems. Fundamental research on volcano infrasound is providing substantial new insights on eruption dynamics and volcanic processes and will continue to do so over the next decade. The increased availability of infrasound sensors will expand observations of varied eruption styles, and the associated increase in data volume will make machine learning workflows more feasible. More sophisticated modeling will be applied to examine infrasound source and propagation effects from...
Journal of Geophysical Research, 2009
1] The period September-November 2007 was characterized at Mount Etna by explosive activity and intense degassing. During this time interval, infrasonic signals were recorded by an infrasonic network. By a triggering procedure, about 1000 infrasonic events were found, characterized by very high signal-to-noise ratio and grouped into nine families. Successively, the spectral analysis allowed subdividing these nine families into three clusters based on the peak frequency and the quality factor of the events. Finally, by the location analysis a cluster (cluster 1) was related to the degassing activity of the northeast crater (NEC), while the other two (clusters 2 and 3) to the explosive activity of the southeast crater (SEC). The comparison between the stacked infrasonic waveforms, interpreted as generated by the vibration of large gas bubbles, and the synthetic ones, permitted to calculate radius, length of the bubble, and initial overpressure, by a genetic algorithm method. The higher overpressure values of cluster 3 compared to the cluster 2 values were in good agreement with the stronger intensity of the explosions accompanying the infrasonic events of cluster 3. The variation of both intensities and waveforms is tentatively attributed to the occasional accumulation of lithic clasts (due to moderate landslides?) on the explosive vent. Indeed, events belonging to cluster 3 were no longer observed once the landslides had ended. Finally, the daily emitted gas volume, related to the active degassing, was estimated for NEC and SEC by using the infrasonic data during the studied period.
Bulletin of Volcanology
Infrasound signals are used to investigate and monitor active volcanoes during eruptive and degassing activity. Infrasound amplitude information has been used to estimate eruptive parameters such as plume height, magma discharge rate, and lava fountain height. Active volcanoes are characterized by pronounced topography and, during eruptive activity, the topography can change rapidly, affecting the observed infrasound amplitudes. While the interaction of infrasonic signals with topography has been widely investigated over the past decade, there has been limited work on the impact of changing topography on the infrasonic amplitudes. In this work, the infrasonic signals accompanying 57 lava fountain paroxysms at Mt. Etna (Italy) during 2021 were analyzed. In particular, the temporal and spatial variations of the infrasound amplitudes were investigated. During 2021, significant changes in the topography around the most active crater (the South East Crater) took place and were reconstruc...
Journal of Volcanology and Geothermal Research, 2011
On 13 May 2008 an eruptive fissure opened on Mount Etna's eastern flank feeding both explosive activity and lava effusion from multiple vents for about 14 months. During the investigated May-September 2008 eruptive period, infrasound recordings from a 4 station-sparse network allowed tracking of the explosive activity in terms of location and dynamics. In order to focus on activity from the eruptive fissure, the infrasonic events generated by the summit craters were selected by using both spectral features and time delays between pairs of stations and excluded from our analysis. Then, to accurately locate events from the fissure, we used a composite method, based on the semblance and brightness functions. This enabled the study of the co-existence of more than one infrasound source and/or its migration along the eruptive fissure. Hence, results permitted us to discriminate the number of active vents and their location along the fissure even when, due to poor weather conditions, it was not possible to access the vents or carry out direct observations. The eruptive activity was characterised by variations in the number of active vents according to the overall intensity of the eruptive event. Variability of the infrasound waveforms highlighted either that distinct vents produced signals with different waveforms, or that single vents generated different events during distinct periods of time, or finally both the previous phenomena. We applied the strombolian bubble vibration model to model waveform differences and attributed the signal variations to bubble radius changes.► Infrasound investigation provides insights into eruptive fissure activity. ► Joint semblance-brightness technique allows very precise locations of eruptive vents. ► Infrasound waveform variability shows different active vents or their time changes.