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.
•FTIR and Multi-GAS measurements at Yasur Volcano constrain volcanic gas compositions•The cyclic variation in gas geochemistry at Yasur is explained by therupture and reforming of a crystal-rich plug.•High fluxes of volcanic gases have persisted at Yasur Volcano for decades
Abstract
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 S
2−
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.
We used low-cost Raspberry Pi ultraviolet (UV) cameras to measure sulphur dioxide (SO2) fluxes from Sabancaya volcano, Peru, during eruptive activity on 27 April 2018. Light dilution corrections were ...made by operating instruments at two distances simultaneously. Estimated SO2 fluxes of 27.1 kgs-1 are higher than previously reported, likely due to the current eruptive episode (ongoing since November 2016). Each eruptive event included frequent (2–3 per minute), ash-rich emissions, forming gas pulses with masses of 3.0–8.2 tonnes SO2. Sustained degassing and lack of overpressure suggest open-vent activity. Mean fluxes are consistent with those measured by a permanent NOVAC station (25.9 kgs-1) located under the plume, with remaining differences likely due to windspeed estimates and sampling rate. Our work highlights the importance of accurate light dilution and windspeed modelling in SO2 retrievals and suggests that co-location of UV cameras with permanent scanning spectrometers may be valuable in providing accurate windspeeds.
Gadolinium-DTPA (Gd-DTPA) is routinely used as a marker for inflammation in MRI to visualize breakdown of the blood–brain barrier (BBB) in multiple sclerosis. Recent data suggest that ultra-small ...superparamagnetic particles of iron oxide (USPIO) can be used to visualize cellular infiltration, another aspect of inflammation. This project aimed to compare the novel USPIO particle SHU555C to the longitudinal pattern of Gd-DTPA enhancement in multiple sclerosis. Nineteen relapsing-remitting patients were screened monthly using Gd-enhanced MRI. In case of new enhancing lesions, USPIO were injected and 24 h later, MRI was performed and blood was collected to confirm USPIO loading of circulating monocytes. Lesion development was monitored by 3 monthly Gd-DTPA-enhanced scans and a final scan 7–11 months after injection. USPIO-enhancement was observed as hyperintensity on T1-weighted images, whereas no signal changes were observed on T2-weighted-gradient-echo images. In 14 patients with disease activity, 188 USPIO-positive lesions were seen, 144 of which were Gd-negative. By contrast, there were a total of 59 Gd-positive lesions, 15 of which were USPIO negative. Three patterns of USPIO-enhancement were seen: (i) focal enhancement; (ii) ring-like enhancement and (iii) return to isointensity of a previously hypointense lesion. The latter pattern was most frequently observed for lesions that turned out to be transiently hypointense on follow-up scans, and ring-enhancing lesions were less likely to evolve into black holes at follow-up than lesions without ring-like USPIO-enhancement; we speculate this to be associated with repair. In 4% of the USPIO-positive/Gd negative lesions, USPIO-enhancement preceded Gd-enhancement by 1 month. USPIO-enhancement remained visible for up to 3 months in 1.5% of all USPIO-positive lesions. In 29% of the lesions enhancing with both contrast agents, USPIO-enhancement persisted whereas Gd-enhancement had already resolved. In conclusion, the new nano-particle SHU555C provides complementary information to Gd-enhanced MRI, probably related to monocyte infiltration. The use of USPIO-enhanced MRI is likely to lead to more insight in the pluriformity of inflammation in multiple sclerosis.
Hawai'i Island often receives extreme (UV Index ≥ 11) solar ultraviolet radiation (UVR). While the UV Index (UVI) has been measured since 1997 at Hawai'i's high-altitude Mauna Loa Observatory (MLO), ...measurements where people live and recreate are rare. We measured UVI on the face of a rotating mannequin head with UVR sensors at its eyes, ears and cheeks while simultaneously measuring the UVI with a zenith-facing sensor at MLO and seven sites at or near sea level from 19 July to 14 August 2018. The mannequin sensors received higher UVR at midmorning and midafternoon than at noon. For example, at sea level the peak UVI at the left cheek was 5.2 at midmorning and 2.9 at noon, while the horizontal UVI at noon was 12.7. Our measurements were supplemented with wide-angle (190° and 360°) sky photographs and UV images of the mannequin head. Because the UVI applies to horizontal surfaces, people in tropical and temperate latitudes should be informed that their face may be more vulnerable to UVR at midmorning and midafternoon than at noon. Finally, our instruments provided opportunities to measure unexpected UVR-altering events, including rare biomass smoke over MLO and spectroscopic measurements of substantial UVR-absorbing sulfur dioxide in the eruption plume of the Kilauea volcano.
Swept coherent optical spectrum analysis is becoming a viable method for subpicometer spectral characterization of optical communications signals. The performance of this technique depends on a ...number of factors that we have investigated both theoretically and experimentally. This includes the influence of signal linewidth, polarization, optical phase, intensity noise, and electrical filtering methods. These effects are discussed in detail and illustrated through spectral measurements on communications transmitters. We extend the heterodyne method to permit measurement of both spectral amplitude and phase of the spectral sidebands. The transformation of the complex optical field spectrum to the time domain waveform is demonstrated.
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.
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.
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.
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