Degassing dynamics of basaltic lava lake at a top-ranking volatile emitter: Ambrym volcano, Vanuatu arc

Abstract

Persistent lava lakes are rare on Earth and provide volcanologists with a remarkable opportunity to directly investigate magma dynamics and degassing at the open air. Ambrym volcano, in Vanuatu, is one of the very few basaltic arc volcanoes displaying such an activity and voluminous gas emission, but whose study has long remained hampered by challenging accessibility. Here we report the first high temporal resolution (every 5 sec) measurements of vigorous lava lake degassing inside its 300 m deep Benbow crater using OP-FTIR spectroscopy. Our results reveal a highly dynamic degassing pattern involving (i) recurrent (100-200 sec) short-period oscillations of the volcanic gas composition and temperature, correlating with pulsated gas emission and sourced in the upper part of the lava lake, (ii) a continuous long period (∼8 min) modulation probably due to the influx of fresh magma at the bottom of the lake, and (iii) discrete CO 2 spike events occurring in coincidence with the sequential bursting of meter-sized bubbles, which indicates the separate ascent of large gas bubbles or slugs in a feeder conduit with estimated diameter of 6±1 m. This complex degassing pattern, measured with unprecedented detail and involving both coupled and 2 decoupled magma-gas ascent over short time scales, markedly differs from that of quieter lava lakes at Erebus and Kilauea. It can be accounted for by a modest size of Benbow lava lake and its very high basalt supply rate (~20 m 3 s -1 ), favouring its rapid overturn and renewal. We verify a typical basaltic arc signature for Ambrym volcanic gas and, based on contemporaneous SO 2 flux measurements, we evaluate huge emission rates of 160

Slug Stability in Flaring Geometries and Ramifications for Lava Lake Degassing

“…We find that in these cases, slugs break up before they reach the flare region. This prediction is consistent with visual observations of chaotic bubbling on the lava lake surface at Ambrym (Allard et al, ) and supported by measurements of persistent gas emissions at Erta Ale and Nyriagonga that suggest the presence of multiple smaller bubbles, rather than a single, conduit‐filling slug (e.g., Sawyer et al, ).…”

“…Mechanisms that could contribute to the episodic eruptions observed at many lava lakes include gas pistoning (e.g., Patrick et al, ; Swanson et al, ), dynamic pressure equilibration (e.g., Witham et al, ), unstable bidirectional conduit flow (e.g., Oppenheimer et al, ), and the intermittent rise of large gas slugs (e.g., Blackburn et al, ; Jaupart & Vergniolle, ; Wilson & Head, ). Of these mechanisms, the slug model has been most commonly invoked (e.g., Allard et al, ; Aster et al, ; Bouche et al, ; Calder et al, ; Gerst et al, ; Johnson et al, ; Pyle et al, ; Vergniolle & Jaupart, ).…”

“…The associated high gas flux drives constant recirculation of the degassing magma, through which the system maintains high heat flux and degasses continually (e.g., Wilson & Head, 1981). Despite the persistent degassing, lava lakes exhibit a wide range of eruptive behavior, from passive and persistent gas loss to energetic explosions, fountaining, and strong gas jetting (Allard et al, 2016;Daly, 1911;Dibble et al, 2008;Johnson et al, 2008;Oppenheimer et al, 2009;Patrick et al, 2011;Perret, 1913).…”

A CO2‐gas precursor to the March 2015 Villarrica volcano eruption

“…Our observations, covering a period of ∼3 months, improve the currently sparse volcanic gas data set for this unique but remote volcano. On a broader scale, our results contribute to a better understanding of lava‐lake degassing dynamics [ Sawyer et al ., , ; Oppenheimer et al ., ; Martin et al ., ; Moussallam et al ., ; Allard et al ., ; Molina et al ., ].…”

From magma ascent to ash generation: investigating volcanic conduit processes by integrating experiments, numerical modeling, and observations

“…Parameters as plume exit velocity and trajectory, mass discharge rates, gas fluxes, gas compositions, and grain size distributions can now be measured in real time using high-speed visual, thermal, infrared and sulfur dioxide cameras [Bani et al 2013, Harris 2013, Bombrum et al 2014, Gaudin et al 2014a, b, Valade et al 2014, Barni et al 2015, Bombrum et al 2015, Cerminara et al 2015, Bombrun et al 2016, Gaudin et al 2016], a combination of thermal camera, weather radar observations and/ or infrasound measurements , De Angelis et al 2016, Vulpiani et al 2016, and open-path Fourier transform infrared (OP-FTIR) spectrometry [La Spina et al 2015, Allard et al 2016. These measurements have highlighted the unsteady nature of these parameters.…”