Multi-Parametric Field Experiment Links Explosive Activity and Persistent Degassing at Stromboli

Abstract

Visually unattainable magmatic processes in volcanic conduits, such as degassing, are closely linked to eruptive styles at the surface, but their roles are not completely identified and understood. To gain insights, a multi-parametric experiment at Stromboli volcano (Aeolian Islands, Italy) was installed in July 2016 focusing on the normal explosive activity and persistent degassing. During this experiment, gas-dominated (type 0) and particle-loaded (type 1) explosions, already defined by other studies, were clearly identified. A FLIR thermal camera, an Ultra-Violet SO₂ camera and a scanning Differential Optical Absorption Spectroscopy were deployed to record pyroclast and SO2 masses emitted during individual explosions, as well as persistent SO₂ fluxes, respectively. An ASHER instrument was also deployed in order to collect ash fallouts and to measure the grain size distribution of the samples. SO2 measurements confirm that persistent degassing was far greater than that emitted during the explosions. Further, we found that the data could be characterized by two periods. In the first period (25–27 July), activity was mainly characterized by type 0 explosions, characterized by high velocity jets. Pyroclast mass fluxes were relatively low (280 kg/event on average), while persistent SO2 fluxes were high (274 t/d on average). In the second period (29–30 July), activity was mainly characterized by type 1 explosions, characterized by low velocity jets. Pyroclast mass fluxes were almost ten times higher (2,400 kg/event on average), while persistent gas fluxes were significantly lower (82 t/d on average). Ash characterization also indicates that type 0 explosions fragments were characterized by a larger proportion of non-juvenile material compared to type 1 explosions fragments. This week-long field experiment suggests that, at least within short time periods, Stromboli’s type 1 explosions can be associated with low levels of degassing and the mass of particles accompanying such explosive events depends on the volume of a degassed magma cap sitting at the head of the magma column. This could make the classic particle-loaded explosions of Stromboli an aside from the true eruptive state of the volcano. Instead, gas-dominated explosions can be associated with high levels of degassing and are indicative of a highly charged (with gas) system. We thus suggest that relatively deep magmatic processes, such as persistent degassing and slug formation can rapidly influence the superficial behavior of the eruptive conduit, modulating the presence or absence of degassed magma at the explosion/fragmentation level.

An interpretative view of open-vent volcanoes

“…The degassing at Stromboli has been extensively described (Fig. 12) and quantified by gas and geophysical studies (Harris and Ripepe 2007;Ripepe et al 2008;Ripepe et al 2005; Del Donne and Ripepe 2012; Thivet et al 2021). The main techniques, which have been used separately or simultaneously, consist into 1) videos in the visible and infrared range and rarely high-speed cameras (Patrick et al 2007;Harris et al 2012;Taddeucci et al 2012a, b;Harris et al 2013;Gaudin et al 2014a;Bombrun et al 2015;Gaudin et al 2017); 2) DOAS, multi-gas, open-path Fourier transform infrared spectroscopy, ultraviolet-cameras for gas studies (Burton et al 2007;Aiuppa et al 2010;Tamburello et al 2012), 3) infrasound, seismicity and radar for geophysical studies (Weill et al 1992;Vergniolle and Brandeis 1994;Chouet et al 1999;2003;Scharff et al 2008;Genco and Ripepe 2010;Del Donne et al 2016;Patanè et al 2017) and 4) laboratory experiments and models (Lane et al 2013;Del Bello et al 2012;.…”

VIGIA: A Thermal and Visible Imagery System to Track Volcanic Explosions

“…In the current state (to June 2022), the VIGIA system captures still images in infrared and visible spectrum, which can be used to perform long term studies, for example, studies of morphology changes (e.g., [65]) and of effusion of lava flows (e.g., [23]). The system automatically recognizes when the volcano is unclouded and when an explosion occurs, then it captures high-temporal resolution thermal videos of the explosion; the resulting videos constitute the input material for studies of explosion or plume dynamics (e.g., [66,67]). VIGIA also records information from temperature, pressure and relative humidity sensors.…”

Standardized analysis of juvenile pyroclasts in comparative studies of primary magma fragmentation; 1. Overview and workflow

“…Yoshimoto et al 2005;Swanson et al 2009;Bustillos et al 2016), have been used to collect sufficient material (within known surface areas) to estimate the magnitude of the event through the mass load per unit area and to obtain a sufficient number of clasts for chemical and textural characterization. More sophisticated devises, designed especially for ash, have been used for collecting ash, but also to measure its load (Bernard 2013;Shimano et al 2013), its grain size and terminal velocity (Freret-Lorgeril et al 2019;Thivet et al 2021).…”