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Abstract:

Rabaul is a caldera volcano on New Britain Island, Papua New Guinea, whose active cone Tavurvur ranks seventh globally for long-term mean SO2 and CO2 emissions. It is unknown why Rabaul is such a strong emitter of volcanic gases. Magma mixing between basaltic and dacitic magmas is envisioned to play a fundamental role in driving eruptions at Rabaul, but the compositions of mafic recharge magmas, their volatile contents, and their contribution to ongoing gas emissions are poorly constrained. Rabaul's recent eruptive history includes the 1994 twin eruption, a VEI 4 eruption in 2006, and a prolonged phase of strong SO2 degassing from late 2006 to 2009 prior to the most recent eruption in 2014. We analysed 84 plagioclase-, clinopyroxene- and olivine-hosted melt inclusions from 2014 Tavurvur volcanic bombs for major, trace and volatile elements (H2O, CO2, SO2, Cl, F), corrected for post-entrapment crystallisation, and combined these data with satellite-derived SO2 retrievals (OMPS, OMI, IASI). Olivine- and high-Mg# clinopyroxene-hosted melt inclusions record basaltic compositions likely representing the mafic recharge magmas of the volcanic system. Low-An plagioclase- and low-Mg# clinopyroxene-hosted melt inclusions are andesitic to dacitic in composition which closely match dacites erupted in caldera-forming eruptions at Rabaul (e.g. the 1400 years B.P. Rabaul Pyroclastics event) and likely record the composition of magma resident in Rabaul's shallow plumbing system. Reverse fractional crystallisation and trace element constraints imply primary volatile contents of ∼1.1–1.9 wt% H2O, 1400–2600 ppm SO2, ∼392 ppm Cl and ∼ 59 ppm F, indicating Rabaul magmas are not anomalously volatile-rich within the global range of subduction zone magmas. Our analyses of satellite data yield a best estimate of SO2 mass of ∼37 kt for the 2014 eruption. Petrological estimates derived from our melt inclusion analyses give ∼110 kt. We attribute the modest 2014 SO2 release to low erupted magma volumes and extensive pre-eruptive degassing of the shallow reservoir between 2006 and 2010, and note that volatile-rich mafic magma was volumetrically minor in the erupted material. Our results reconcile melt-inclusion and satellite records and constrain the roles of magma mixing and prior degassing in governing Rabaul's gas output.

Abstract:

The eruption of Hunga volcano on 15 January 2022 was an exceptional event in the satellite era. Record-breaking heights of the volcanic plume were reported, a large amount of water was injected into the stratosphere and a broad spectrum of atmospheric waves were detected. Here, we use satellite measurements to show that a transient ring of small ice particles (~2 μm) formed around the plume. We hypothesize that the ice ring was generated by the passage of an atmospheric wave triggered by a pressure pulse at the surface corresponding to a violent explosion that occurred during the 15 January 2022 eruption sequence. The passage of the atmospheric wave produced a transient rarefaction in the upper troposphere-lower stratosphere, which in turn led to oscillations in ambient temperature. Due to the supersaturated state of the atmosphere with respect to ice, ice particles formed in the wake of the radially propagating atmospheric wave, allowing an exceptional opportunity to study ice particle growth via vapour deposition. This atmospheric phenomenon serves as an important natural experiment that reveals the time scale on which ice particles nucleate and grow given an abrupt perturbation in ambient temperature.

Abstract:

300–400 km in diameter. Previous reports showed that one of these entities was traceable for 3 months. Anticyclonic circulation was also previously reported. We present multiple lines of evidence to characterize these cloud subelements by their spatial confinement, morphology, and sulfate-dominated aerosol aspect, which was evident from plume onset. In addition, we show that they were ably identifiable in geostationary satellite “cirrus channel” reflectance imagery and had an enduring signal of window infrared absorption, detectable for at least 1 month. The term we apply to this phenomenon is “sulfate/SO₂ anticyclonic contained circulation,” abbreviated SSACC. Anticyclonic circulation is first detectable on 24 June, 2 days posteruption. Two SSACCs persist beyond June. One is traceable until mid-August over Canada. The other SSACC was discernible until 5 October after having completed three global circumnavigations. The internal SSACC circulation aspect is gleaned from geostationary-based visible image animations and confirmed in situ via a novel application of high-resolution radiosonde wind direction and balloon position data. We also examine diabatic lofting of both SSACCs in relation to their individual geographic and constituent morphologies. Thermal infrared observations show that SSACC aerosols produce brightness temperature depressions of ~2.6 K, opening a new line of investigation into the source of heating that contributes to diabatic rise.

Abstract:

Volcanic ash clouds are carefully monitored as they present a significant hazard to humans and aircraft. The primary tool for forecasting the transport of ash from a volcano is dispersion modelling. These models make a number of assumptions about the size, sphericity and density of the ash particles. Few studies have measured the density of ash particles or explored the impact that the assumption of ash density might have on the settling dynamics of ash particles. In this paper, the raw apparent density of 23 samples taken from 15 volcanoes are measured with gas pycnometry, and a negative linear relationship is found between the density and the silica content. For the basaltic ash samples, densities were measured for different particle sizes, showing that the density is approximately constant for particles smaller than 100 µm, beyond which it decreases with size. While this supports the current dispersion model used by the London Volcanic Ash Advisory Centre (VAAC), where the density is held at a constant (2.3 g cm-3), inputting the measured densities into a numerical simulation of settling velocity reveals a primary effect from the silica content changing this constant. The VAAC density overestimates ash removal times by up to 18 %. These density variations, including those varying with size beyond 100 µm, also impact short-range particle-size distribution (PSD) measurements and satellite retrievals of ash.