Bubbles in Basalts: Measuring and Modelling Basaltic Degassing

Basaltic degassing is driven by the release of CO2, H2O, and SO2. Hitherto, the measurement of SO2 has been commonplace due to the lack of significant ambient atmospheric content. UV camera technology is currently among the best of techniques to measure this SO2 release from volcanoes given its high spatial and temporal resolutions. Given that an elevated CO2 flux can be an indication of magma movement at depth, a reliable method of measuring this species at similarly high temporal resolutions would be valuable. A technique making this possible is described here. This technique combines measurements of SO2 flux at Mt. Etna, using a UV camera, with CO2/SO2 gas ratios, which when multiplied together allow the creation of a contemporaneous CO2 flux datasets at a time resolution of ≈ 1 Hz. This also allowed the comparison of degassing with infrasonic and seismic datasets. This comparison was facilitated by the development of a new analysis technique to investigate correlative trends between noisy environmental datasets. The technique works by combining the continuous wavelet transform of two separate signals, with correlation of their respective coefficients at matching timescales using Spearman’s rank to produce a visually intuitive graphical plot. This revealed intriguing links between CO2 degassing and seismicity. Stromboli is renowned for its regular explosive activity. Through a permanent network of UV cameras at the summit area, a large number of explosive (120) and puffing events (80) were characterised in terms of their explosive and coda masses, termed the total strombolian event mass. Through this analysis, it was discovered that a large proportion of gas for each strombolian event is contained within the coda, ≈ 53 to 75% and for hornito events ≈ 70 to 84 %. The events were also characterised into six separate groups according to gas release pattern following the main eruptive burst. Through computational fluid dynamical simulations, for a range of appropriate strombolian eruption gas masses, the results demonstrated that there is potential for the release of daughter bubbles from the base of rising slugs. These daughter bubbles act to reduce the mass of slugs and can make slug flow unsustainable. Models were initiated over a suitable range of event masses, which demonstrated that ≈ 43 to 69% of the initial slug masses was released into the daughter bubble train. By applying the average mass loss rate, of ≈ 13.2 kg s-1, with total event masses, slugs are unlikely to be self-sustainable below depths of ≈ 740 m. A non-linear relationship between the dimensionless inverse viscosity term, N_f, and mass loss rate was also discovered. Also noted for its explosive activity is Mt. Etna. This activity includes hard to measure strombolian activity. During a rare period of activity at the Bocca Nuova summit crater ≈ 27 minutes of frequent but mild strombolian behaviour was captured using a UV camera. Given the unorthodox use of a rock background for the reflectance of light, calibration was tested and performed successfully on a basaltic background at the summit. Results show an SO2 mass range of ≈ 0.1 – 14 kg and a total gas mass range, on combination with measured Multi-GAS ratios, of ≈ 0.2 – 74 kg. Compared to events at Stromboli the activity was more frequent with an ≈ 4 s modal repose and with much lower overall masses. On investigating temporal trends between events it was observed that the largest mass events were followed by longer repose periods before another event occurred, smaller events occurring more frequently, a feature which is termed repose gap behaviour. Given the rapidity and mass of events it is reasonable that this activity was driven by gas slugs and that they were travelling in close proximity to each other. Using existing fluid dynamical models for the wake interaction length, an area behind a slug where a trailing slug can begin to interact with a leading one, it is possible that slugs are close enough to interact and coalesce. Indeed, this would provide a plausible mechanism for the repose gap. Building on the observations in the field at Mt. Etna a series of analogue laboratory experiments and computational fluid dynamics models were devised to investigate rapid strombolian activity, that driven by slugs. Behaviour of slugs acting independently of one another in a single-slug volcanic regime have been investigated thoroughly, however, the behaviour of slugs in a multi-slug volcanic regime have been neglected, largely a result of its comparative complexity. Laboratory experiments allowed the investigation of a series of average gas flow rates and hence slug lengths (i.e. overall gas volume fractions). The rates of expansion were also varied to simulate slug flow at depth and nearer to the magma surface. In particular, the process of coalescence was investigated. By comparing slug length at burst with repose time the repose gap feature was also identified. Given that values for rise speed, liquid, and conduit dimensions are known, this enabled the definition of the minimum period of repose as the wake length plus the length of the slug all divided by the rise speed of the base of the slug. This relation is validated successfully on the laboratory data and also on the collected Etna data. Additionally the laboratory analysis identified a previously unidentified feature whereby coalescence can occur between rising slugs, even when the trailing slug base is rising at a slower speed than the leading. This is likely related to the expansions of gas slugs. Computational fluid dynamics identified similar processes whereby the gap between identically massed slugs was maintained by slug expansion which acted to increase the speed of slugs above them. It is only when slugs are initiated within the wake length that coalescence occurs. Further relationships were discovered between slug rise speed and gas volume fraction, whereby the average rise speed of a slug increases with regime volume fraction, and burst slug length and volume fraction. Finally, building on the repose gap observations and developed relation, the observed relationships between slug length and gas rise speed with gas volume fraction are used to develop two separate models categorising the styles of volcanic activity which will be prevalent. The first, slug length model, is based upon repose time and slug lengths, with the second based upon overall volume fraction and repose time. The slug length model splits activity into: passive, puffing, strombolian explosive and strombolian rapid. This model performs well when applied to strombolian events, successfully differentiating between explosive and passive events. The volume fraction model applies fluid dynamical relationships for transitions to churn and annular flow, in addition to the already defined strombolian relationships, assumed here to play some part in defining the transition to hawaiian lava fountaining activity. This allows the definition of critical volume fractions above which large gas slugs or pockets can burst with increasing frequency until full lava fountaining behaviour is realised. Both models allow eruption parameters to be estimated via the delay time between events or vice versa. On comparison of known correlative relationships between gas emissions and seismicity a log relationship is discovered when all events are normalised to comparable parameters, suggesting that seismicity could also be incorporated into such a model in the future. In particular, the latter volume fraction model is the first step in developing a unifying theory of basaltic degassing based on a varying delay between events and could be particularly useful when used in tandem with real time gas emission data for eruption forecasting and understanding the fluid dynamical flow processes occurring in the sub-surface

Strombolian eruptions and dynamics of magma degassing at Yasur Volcano (Vanuatu)

Open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux, largely through passive degassing and mild explosive activity. We present volcanic gas flux and composition data from Yasur Volcano, Vanuatu collected in July 2018. The average volcanic plume chemistry is characterised by a mean molar CO2/SO2 ratio of 2.14, H2O/SO2 of 148 and SO2/HCl of 1.02. The measured mean SO2 flux in the period of 6th to 9th July is 4.9 kg s−1. Therefore, the mean fluxes of the other species are 7.5 kg∙s−1 CO2, 208 kg∙s−1 H2O and 4.8 kg∙s−1 HCl. The degassing regime at Yasur volcano ranges from ‘passive’ to ‘active’ styles, with the latter including Strombolian activity and spattering. Gases emitted during active degassing are enriched in SO2 over HCl and CO2 over SO2 relative to passive degassing, with CO2/SO2 ratios of 2.85 ± 0.17, SO2/HCl of 1.6 ± 0.22, and H2O/SO2 of 315 ± 78.8. Gases emitted during passive degassing have CO2/SO2 ratios of 1.96 ± 0.12, SO2/HCl of 0.50 ± 0.07 and H2O/SO2 of 174 ± 43.5. We use a model of volatile degassing derived from melt inclusion studies (Metrich et al., 2011), combined with our observations of chemical variations in the outgassing bubbles to propose a mechanism for magma degassing in the conduit at Yasur. We envisage a shallow conduit filled with crystal-rich magma, forming a viscous and mobile plug that develops an effective yield strength from the surface to a depth of at least 2000 m, in which bubbles are trapped, grow, ascend towards the surface and burst in a typical Strombolian eruption. Deeper bubbles released during active degassing are enriched in CO2 and SO2 compared to bubbles released during ‘passive degassing’, which are sourced from close to the surface, and are, consequently, HCl-rich

Strombolian eruptions and dynamics of magma degassing at Yasur Volcano (Vanuatu)

Open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux, largely through passive degassing and mild explosive activity. We present volcanic gas flux and composition data from Yasur Volcano, Vanuatu collected in July 2018. The average volcanic plume chemistry is characterised by a mean molar CO2/SO2 ratio of 2.14, H2O/SO2 of 148 and SO2/HCl of 1.02. The measured mean SO2 flux in the period of 6th to 9th July is 4.9 kg s−1. Therefore, the mean fluxes of the other species are 7.5 kg∙s−1 CO2, 208 kg∙s−1 H2O and 4.8 kg∙s−1 HCl. The degassing regime at Yasur volcano ranges from ‘passive’ to ‘active’ styles, with the latter including Strombolian activity and spattering. Gases emitted during active degassing are enriched in SO2 over HCl and CO2 over SO2 relative to passive degassing, with CO2/SO2 ratios of 2.85 ± 0.17, SO2/HCl of 1.6 ± 0.22, and H2O/SO2 of 315 ± 78.8. Gases emitted during passive degassing have CO2/SO2 ratios of 1.96 ± 0.12, SO2/HCl of 0.50 ± 0.07 and H2O/SO2 of 174 ± 43.5. We use a model of volatile degassing derived from melt inclusion studies (Metrich et al., 2011), combined with our observations of chemical variations in the outgassing bubbles to propose a mechanism for magma degassing in the conduit at Yasur. We envisage a shallow conduit filled with crystal-rich magma, forming a viscous and mobile plug that develops an effective yield strength from the surface to a depth of at least 2000 m, in which bubbles are trapped, grow, ascend towards the surface and burst in a typical Strombolian eruption. Deeper bubbles released during active degassing are enriched in CO2 and SO2 compared to bubbles released during ‘passive degassing’, which are sourced from close to the surface, and are, consequently, HCl-rich

Low-cost 3D printed 1 nm resolution smartphone sensor-based spectrometer: instrument design and application in ultraviolet spectroscopy.

We report on the development of a low-cost spectrometer, based on off-the-shelf optical components, a 3D printed housing, and a modified Raspberry Pi camera module. With a bandwidth and spectral resolution of ≈60  nm and 1 nm, respectively, this device was designed for ultraviolet (UV) remote sensing of atmospheric sulphur dioxide (SO2), ≈310  nm. To the best of our knowledge, this is the first report of both a UV spectrometer and a nanometer resolution spectrometer based on smartphone sensor technology. The device performance was assessed and validated by measuring column amounts of SO2 within quartz cells with a differential optical absorption spectroscopy processing routine. This system could easily be reconfigured to cover other UV-visible-near-infrared spectral regions, as well as alternate spectral ranges and/or linewidths. Hence, our intention is also to highlight how this framework could be applied to build bespoke, low-cost, spectrometers for a range of scientific applications

Low-Cost Hyperspectral Imaging with A Smartphone.

Recent advances in smartphone technologies have opened the door to the development of accessible, highly portable sensing tools capable of accurate and reliable data collection in a range of environmental settings. In this article, we introduce a low-cost smartphone-based hyperspectral imaging system that can convert a standard smartphone camera into a visible wavelength hyperspectral sensor for ca. £100. To the best of our knowledge, this represents the first smartphone capable of hyperspectral data collection without the need for extensive post processing. The Hyperspectral Smartphone's abilities are tested in a variety of environmental applications and its capabilities directly compared to the laboratory-based analogue from our previous research, as well as the wider existing literature. The Hyperspectral Smartphone is capable of accurate, laboratory- and field-based hyperspectral data collection, demonstrating the significant promise of both this device and smartphone-based hyperspectral imaging as a whole

Dynamics of Outgassing and Plume Transport Revealed by Proximal Unmanned Aerial System (UAS) Measurements at Volcán Villarrica, Chile

Volcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing, and, on geological timescales, constitute an important source of volatiles to the Earth’s atmosphere. Measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles. However, significant gaps remain in our global inventories of volcanic emissions, (particularly for CO2, which requires proximal sampling of a concentrated plume) for those volcanoes where the near-vent region is hazardous or inaccessible. Unmanned Aerial Systems (UAS) provide a robust and effective solution to proximal sampling of dense volcanic plumes in extreme volcanic environments. Here, we present gas compositional data acquired using a gas sensor payload aboard a UAS flown at Volcán Villarrica, Chile. We compare UAS-derived gas timeseries to simultaneous crater rim multi-GAS data and UV camera imagery to investigate early plume evolution. SO2 concentrations measured in the young proximal plume exhibit periodic variations that are well-correlated with the concentrations of other species. By combining molar gas ratios (CO2/SO2 = 1.48–1.68, H2O/SO2 = 67–75 and H2O/CO2 = 45–51) with the SO2 flux (142 ± 17 t/day) from UV camera images, we derive CO2 and H2O fluxes of ~150 t/day and ~2850 t/day, respectively. We observe good agreement between time-averaged molar gas ratios obtained from simultaneous UAS- and ground-based Multi-GAS acquisitions. However, the UAS measurements made in the young, less diluted plume reveal additional short-term periodic structure that reflects active degassing through discrete, audible gas exhalations.Alfred P. Sloan Foundation; Leverhulme Trus

A rapidly convecting lava lake at Masaya Volcano, Nicaragua

Lava lakes provide a rare opportunity to study conduit flow processes through direct observation of the exposed magma surface. The recent lava lake activity at Masaya volcano (Nicaragua), which commenced in 2015, displayed several unusual phenomena. We report on the dynamics of this rapidly convecting lake, which, to the best of our knowledge manifested the highest lava flow velocities ever reported for a lava lake: 13.7–16.4 m s−1, in addition to unusual fluid dynamic behavior involving alteration in surface flow direction. We studied this system with multiparametric and high time resolution remote sensing measurements, performed during June 2017, including ultraviolet camera observations of SO2 emission rates, near infrared thermal camera measurements and video analyses of the lake surface. Median SO2 emission rates of 3.1 (±0.8) and 3.7 (±0.9) kg s−1 were found, which are lower than previously published estimates, and could represent challenging remote sensing conditions or a waning in lava lake activity. Video analyses enabled characterization of frequent bursts of approximately hemispherical spherical-cap bubbles on the surface with diameters ranging 0.6–8.5 m (median of 2.6 m), and calculation of individual bubble masses, which contribute to active bubble bursting values estimated at 1.9 to 3.9 kg s−1. We show that only a small fraction, 7–17%, of total emission volumes are contributed by these bubbles, based on estimated emission rates of 22.5 and 26.9 kg s−1. Furthermore, periodicity analysis reveals regular 200–300 s oscillations in SO2 emissions. These are not shared by any of our other datasets and particularly during the contemporaenously acquried thermal data, hence, we tentatively assign an atmospheric causal generation mechanism, driven by atmospheric transport and turbulence phenomena, such as eddying. Overall, we highlight the uniquely high velocity and fluid dynamic behavior of Masaya lava lake

Volatile metal emissions from volcanic degassing and lava–seawater interactions at Kīlauea Volcano, Hawai’i

Funder: EPSRC-CASE studentshipFunder: NERC studentshipFunder: Leverhulme Trust; doi: https://doi.org/10.13039/501100000275Funder: NERC-CASE studentshipFunder: Rolex InstituteAbstract: Volcanoes represent one of the largest natural sources of metals to the Earth’s surface. Emissions of these metals can have important impacts on the biosphere as pollutants or nutrients. Here we use ground- and drone-based direct measurements to compare the gas and particulate chemistry of the magmatic and lava–seawater interaction (laze) plumes from the 2018 eruption of Kīlauea, Hawai’i. We find that the magmatic plume contains abundant volatile metals and metalloids whereas the laze plume is further enriched in copper and seawater components, like chlorine, with volatile metals also elevated above seawater concentrations. Speciation modelling of magmatic gas mixtures highlights the importance of the S2− ligand in highly volatile metal/metalloid degassing at the magmatic vent. In contrast, volatile metal enrichments in the laze plume can be explained by affinity for chloride complexation during late-stage degassing of distal lavas, which is potentially facilitated by the HCl gas formed as seawater boils

High-Resolution Hyperspectral Imaging Using Low-Cost Components: Application within Environmental Monitoring Scenarios

High-resolution hyperspectral imaging is becoming indispensable, enabling the precise detection of spectral variations across complex, spatially intricate targets. However, despite these significant benefits, currently available high-resolution set-ups are typically prohibitively expensive, significantly limiting their user base and accessibility. These limitations can have wider implications, limiting data collection opportunities, and therefore our knowledge, across a wide range of environments. In this article we introduce a low-cost alternative to the currently available instrumentation. This instrument provides hyperspectral datasets capable of resolving spectral variations in mm-scale targets, that cannot typically be resolved with many existing low-cost hyperspectral imaging alternatives. Instrument metrology is provided, and its efficacy is demonstrated within a mineralogy-based environmental monitoring application highlighting it as a valuable addition to the field of low-cost hyperspectral imaging

Ultraviolet Imaging with Low Cost Smartphone Sensors: Development and Application of a Raspberry Pi-Based UV Camera

Here, we report, for what we believe to be the first time, on the modification of a low cost sensor, designed for the smartphone camera market, to develop an ultraviolet (UV) camera system. This was achieved via adaptation of Raspberry Pi cameras, which are based on back-illuminated complementary metal-oxide semiconductor (CMOS) sensors, and we demonstrated the utility of these devices for applications at wavelengths as low as 310 nm, by remotely sensing power station smokestack emissions in this spectral region. Given the very low cost of these units, ≈ USD 25, they are suitable for widespread proliferation in a variety of UV imaging applications, e.g., in atmospheric science, volcanology, forensics and surface smoothness measurements