Magma and Volatile Supply to Post-collapse Volcanism and Block Resurgence in Siwi Caldera (Tanna Island, Vanuatu Arc)

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

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“…Vanuatu (Métrich et al, 2011) and, more broadly, for basaltic arc volcanism (e.g. Kelley and 292 Cottrell, 2009).…”

Section: Average Composition Of Benbow Basaltic Gas 259 260mentioning

confidence: 99%

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

Allard

Burton

Sawyer

et al. 2016

Earth and Planetary Science Letters

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“…7). Water vapour flux at Yasur exceeds 13 × 10 3 Mg day −1 (Métrich et al, 2011). Emissions of water vapour into the atmosphere at Kīlauea and Piton de la Fournaise will be even greater due to the additional contribution of evaporated seawater where lava flows meet the sea (e.g.…”

Section: Evidence For Volcanic Aerosol Indirect Effectsmentioning

confidence: 99%

Systematic satellite observations of the impact of aerosols from passive volcanic degassing on local cloud properties

et al. 2014

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Abstract. The impact of volcanic emissions, especially from passive degassing and minor explosions, is a source of uncertainty in estimations of aerosol indirect effects. Observations of the impact of volcanic aerosol on clouds contribute to our understanding of both present-day atmospheric properties and of the pre-industrial baseline necessary to assess aerosol radiative forcing. We present systematic measurements over several years at multiple active and inactive volcanic islands in regions of low present-day aerosol burden. The time-averaged indirect aerosol effects within 200 km downwind of island volcanoes are observed using Moderate Resolution Imaging Spectroradiometer (MODIS, 2002–2013) and Advanced Along-Track Scanning Radiometer (AATSR, 2002–2008) data. Retrievals of aerosol and cloud properties at Kīlauea (Hawai'i), Yasur (Vanuatu) and Piton de la Fournaise (la Réunion) are rotated about the volcanic vent to be parallel to wind direction, so that upwind and downwind retrievals can be compared. The emissions from all three volcanoes – including those from passive degassing, Strombolian activity and minor explosions – lead to measurably increased aerosol optical depth downwind of the active vent. Average cloud droplet effective radius is lower downwind of the volcano in all cases, with the peak difference ranging from 2–8 μm at the different volcanoes in different seasons. Estimations of the difference in Top of Atmosphere upward Short Wave flux upwind and downwind of the active volcanoes from NASA's Clouds and the Earth's Radiant Energy System (CERES) suggest a downwind elevation of between 10 and 45 Wm−2 at distances of 150–400 km from the volcano, with much greater local (< 80 km) effects. Comparison of these observations with cloud properties at isolated islands without degassing or erupting volcanoes suggests that these patterns are not purely orographic in origin. Our observations of unpolluted, isolated marine settings may capture processes similar to those in the pre-industrial marine atmosphere.

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“…600-700 tonnes/day of SO 2 - Bani and Lardy, 2007;Bani et al, 2013) then we can infer what the vent areavelocity product should be. Metrich et al (2011) suggest the H 2 O/SO 2 ratio at Yasur is 50-90 (nominally 70), and thus the gas is about 5% by mass SO 2 . Thus (assuming the total Yasur SO 2 flux distributed equally between 3 vents) the vent flux of 200 tonnes/day or~2 kg/s SO 2 requires a total gas flux, dominated by H 2 O, of about 50 kg/s.…”

Section: Spectral Analysis and Vent Velocitymentioning

confidence: 98%

“…For a water-vapor dominated gas composition (e.g. Metrich et al, 2011) and temperatures of~1000 K, the sound speed is of the order of 700 m/s, about double that in the ambient air. A 263 Hz emission would be associated, then, with a L~1.3 m cavity, perhaps not an unreasonable value.…”

Section: Spectral Analysis and Vent Velocitymentioning

confidence: 99%

The roar of Yasur: Handheld audio recorder monitoring of Vanuatu volcanic vent activity

Lorenz

Turtle

Howell

et al. 2016

Journal of Volcanology and Geothermal Research

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Magma and Volatile Supply to Post-collapse Volcanism and Block Resurgence in Siwi Caldera (Tanna Island, Vanuatu Arc)

Cited by 90 publications

References 55 publications

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

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

Systematic satellite observations of the impact of aerosols from passive volcanic degassing on local cloud properties

The roar of Yasur: Handheld audio recorder monitoring of Vanuatu volcanic vent activity

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