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The conditions under which halogens partition in favor of an exsolved fluid relative to the coexisting melt are key for understanding many magmatic processes, including volcanic degassing, evolution of crustal melt bodies, and ore formation. We report new F, Cl, and Br fluid/melt partition coefficients for intermediate to silicic melts, for which F and Br data are particularly lacking; and for varying CO2-H2O contents to assess the effects of changing fluid composition (XH2O) on Br fluid/melt partitioning for the first time. The experiments were conducted at pressures 50–120 MPa, temperatures 800–1100 °C, and volatile compositions [molar XH2O = H2O/(H2O +CO2)] of 0.55 to 1, with redox conditions around the Nickel-Nickel Oxygen buffer (fO2 ≈ NNO). Experiments were not doped with Cl, Br, or F and were conducted on natural crystal-bearing volcanic products at conditions close to their respective pre-eruptive state. The experiments therefore provide realistic constraints on halogen partitioning at naturally occurring, brine-undersaturated conditions. Measurements of Br, Cl, and F were made by Secondary Ion Mass Spectrometry (SIMS) on 13 experimental glass products spanning andesite to rhyolitic compositions, together with their natural starting materials from Kelud volcano, Indonesia, and Quizapu volcano, Chile. Fluid compositions were constrained by mass balance. Average bulk halogen fluid/melt partition coefficients and standard deviations are: DClfluid/melt = 3.4 (±3.7 1 s.d.), DFfluid/melt = 1.7 (±1.7), and DBrfluid/melt = 7.1 (±6.4) for the Kelud starting material (bulk basaltic andesite), and DClfluid/melt = 11.1 (±3.5), DFfluid/melt = 0.8 (±0.8), and DBrfluid/melt = 31.3 (±20.9) for Quizapu starting material (bulk dacite). The large range in average partition coefficients is a product of changing XH2O, pressure and temperature. In agreement with studies on synthetic melts, our data show an exponential increase of halogen Dfluid/melt with increasing ionic radius, with partitioning behavior controlled by melt composition according to the nature of the complexes forming in the melt (e.g., SiF4, NaCl, KBr). The fundamental chemistry of the different halogens (differing ionic size and electronegativities) controls the way in which partitioning responds to changes in melt composition and other variables. Experimental results confirm that more Cl partitions into the fluid at higher bulk Cl contents, higher melt Na, higher fluid XH2O ratios, and lower temperatures. Bromine shows similar behavior, though it seems to be more sensitive to temperature and less sensitive to Na content and XH2O. In contrast, F partitioning into the fluid increases as the melt silica content decreases (from 72 to 56 wt% SiO2), which we attribute to the lower abundance of Si available to form F complexes in the melt. These new data provide more insights into the conditions and processes that control halogen degassing from magmas and may help to inform the collection and interpretation of melt inclusions and volcano gas data.

The caldera-forming Samalas eruption of the Samalas–Rinjani volcanic complex on Lombok, Indonesia, in 1257 CE ranks as one of the most explosive and sulphur-rich eruptions of the past thousand years. Along with other significant events (e.g. Tambora 1815, El Chichón 1982), Samalas 1257 forms a class of powerful eruptions of magmas of intermediate alkaline composition, which remain relatively understudied. This study aims to better understand the pre-eruptive magma reservoir conditions and volatile storage capacities of intermediate alkaline systems, using the 1257 Samalas eruption as a case study. Systematic partial-equilibrium experiments were run to constrain potential magma reservoir conditions (25–200 MPa and 850–1000°C) by examining changes in the chemistry and textures of experimental glass and mineral products. Natural trachydacite pumice from the 1257 Samalas eruption was used as the experimental charge for a series of water-saturated experiments run in cold-seal pressure vessels, buffered at an oxygen fugacity ƒO2 of NNO/NNO + 1 log units. Assessing the match between natural and experimental glass compositions and mineral phases and textures reveals that pre-eruptive magma reservoir conditions were between 875°C and 930°C and ca. 100–150 MPa (4.5 ± 1km depth). Breakdown of experimental amphibole at pressures below 75 MPa, and plagioclase instability at 950°C/100 MPa, provide the strongest constraints on phase stabilities that are consistent with the magma storage region. In the observed temperature and pressure range, the natural compositions of plagioclase, amphibole and orthopyroxene are replicated in experimentally precipitated rims. Clinopyroxene and high anorthite plagioclase (An>64) in the natural mineral assemblage could not be replicated in the experiments, implying that these compositions most likely did not grow in the shallow pre-eruptive reservoir of Mt Samalas. The pre-eruptive storage depths of trachydacite magma are significantly shallower than the postulated magma storage at the currently active basaltic-andesite magmatic system at Rinjani, and thus monitoring magma storage depth may be a useful indicator of changing magma composition in the future. Our findings show that highly explosive VEI 7 eruptions of intermediate alkaline magma can be fed from a relatively limited range of storage pressures (100–150 MPa), suggesting accumulation of magma in one place, rather than the rapid extraction of magma from a vertically extensive, transcrustal magma system.

Gas and particulate matter (PM) emissions from Masaya volcano, Nicaragua, cause substantial regional volcanic air pollution (VAP). We evaluate the suitability of low-cost SO2 and PM sensors for a continuous air-quality network. The network was deployed for six months in five populated areas (4–16 km from crater). The SO2 sensors failed and recorded erroneous values on multiple occasions, likely due to corrosion, requiring significant maintenance commitment. The PM sensors were found to be robust but data required correction for humidity. SO2 measurements could not be used as stand-alone tools to detect occurrence of VAP episodes (VAPE), but an SO2/PM correlation reliably achieved this at near-field stations, as confirmed by meteorological forecasts and satellite imagery. Above-background PM concentrations reliably identified VAPE at both near-field and far-field stations. We suggest that a continuous network can be built from a combination of low-cost PM and SO2 sensors with a greater number of PM-only sensors.

Understanding the timing of critical changes in volcanic systems, such as the beginning and end of eruptive behaviour, is a key goal of volcanic monitoring. Traditional approaches to forecasting these changes have used models motivated by the underlying physics of eruption onset, which assume that geophysical precursors will consistently display similar patterns prior to transition in volcanic state. We present a machine learning classification approach for detecting significant changes in patterns of volcanic activity, potentially signalling transitions during the onset or end of volcanic activity, which does not require a model of the physical processes underlying critical changes. We apply novelty detection, where models are trained only on data prior to eruption, to the precursory unrest at Augustine Volcano, Alaska in 2005. This approach looks promising for geophysically-monitored volcanic systems which have been in repose for some time, as no eruptive data is required for model training. We compare novelty detection results with multi32 class classification, where models are trained on examples of both non-eruptive and eruptive data. We contextualise the results of these classification models using constraints from petrological, satellite and visual observations from the 2006 eruption of Augustine Volcano. The transition from non-eruptive to eruptive behaviour we identify in mid-November 2005 is in agreement with previous estimates of the initiation of dike intrusion prior to the 2006 eruption. We find that models which include multiple types of data (seismic, deformation and gas emissions) can better distinguish between non-eruptive and eruptive data than models formulated on single data types.

Explosive, caldera-forming eruptions are exceptional and hazardous volcanic phenomena. The 1883 eruption of Krakatau is the largest such event for which there are detailed contemporary written accounts, allowing information on the eruptive progression to be integrated with the stratigraphy and geochemistry of its products. Freshly exposed sequences of the 1883 eruptive deposits of Krakatau, stripped of vegetation by a tsunami generated by the flank collapse of Anak Krakatau in 2018, shed new light on the eruptive sequence. Matrix glass from the base of the stratigraphy is chemically distinct and more evolved than the overlying sequence indicating the presence of a shallow, silicic, melt-rich region that was evacuated during the early eruptive activity from May 1883 onwards. Disruption of the shallow, silicic magma may have led to the coalescence and mixing of chemically similar melts representative of a range of magmatic conditions, as evidenced by complex and varied plagioclase phenocryst zoning profiles. This mixing, over a period of two to three months, culminated in the onset of the climactic phase of the eruption on 26th August 1883. Pyroclastic density currents (PDCs) emplaced during this phase of the eruption show a change in transport direction from north east to south west, coinciding with the deposition of a lithic lag breccia unit. This may be attributed to partial collapse of an elevated portion of the island, resulting in the removal of a topographic barrier. Edifice destruction potentially further reduced the overburden on the underlying magmatic system, leading to the most explosive and energetic phase of the eruption in the morning of 27th August 1883. This phase of the eruption culminated in a final period of caldera collapse, which is recorded in the stratigraphy as a second lithic lag breccia. The massive PDC deposits emplaced during this final phase contain glassy blocks up to 8 m in size, observed for the first time in 2019, which are chemically similar to the pyroclastic sequence. These blocks are interpreted as representing stagnant, shallow portions of the magma reservoir disrupted during the final stages of caldera formation. This study provides new evidence for the role that precursory eruptions and amalgamation of shallow crustal magma bodies potentially play in the months leading up to caldera-forming eruptions.

Oceanic Anoxic Event 2 (OAE 2), during the Cenomanian–Turonian transition (∼94 Ma), was the largest perturbation of the global carbon cycle in the mid-Cretaceous and can be recognized by a positive carbon-isotope excursion in sedimentary strata. Although OAE 2 has been linked to large-scale volcanism, several large igneous provinces (LIPs) were active at this time (e.g. Caribbean, High Arctic, Madagascan, Ontong-Java) and little clear evidence links OAE 2 to a specific LIP. The Mid-Cenomanian Event (MCE, ∼96 Ma), identified by a small, 1 ‰ positive carbon-isotope excursion, is often referred to as a prelude to OAE 2. However, no underlying cause has yet been demonstrated and its relationship to OAE 2 is poorly constrained. Here, we report sedimentary mercury (Hg) concentration data from four sites, three from the southern margin of the Western Interior Seaway and one from Demerara Rise, in the equatorial proto-North Atlantic Ocean. We find that, in both areas, increases in mercury concentrations and Hg/TOC ratios coincide with the MCE and the OAE 2. However, the increases found in these sites are of a lower magnitude than those found in records of many other Mesozoic events, possibly characteristic of a marine rather than atmospheric dispersal of mercury for both events. Combined, the new mercury data presented here are consistent with an initial magmatic pulse at the time of the MCE, with a second, greater pulse at the onset of OAE 2, possibly related to the emplacement of LIPs in the Pacific Ocean and/or the High Arctic.

Deep carbon emissions from historically inactive volcanoes, hydrothermal, and tectonic structures are among the greatest unknowns in the long-term (∼Myr) carbon cycle. Recent estimates of diffuse CO2 flux from the Eastern Rift of the East African Rift System (EARS) suggest this could equal emissions from the entire mid-ocean ridge system. We report new CO2 surveys from the Main Ethiopian Rift (MER, northernmost EARS), and reassess the rift-related CO2 flux. Since degassing in the MER is concentrated in discrete areas of volcanic and off-edifice activity, characterization of such areas is important for extrapolation to a rift-scale budget. Locations of hot springs and fumaroles along the rift show numerous geothermal areas away from volcanic edifices. With these new data, we estimate total CO2 emissions from the central and northern MER as 0.52–4.36 Mt yr−1. Our extrapolated flux from the Eastern Rift is 3.9–32.7 Mt yr−1 CO2, overlapping with lower end of the range presented in recent estimates. By scaling, we suggest that 6–18 Mt yr−1 CO2 flux can be accounted for by magmatic extension, which implies an important role for volatile-enriched lithosphere, crustal assimilation, and/or additional magmatic intrusion to account for the upper range of flux estimates. Our results also have implications for the nature of volcanism in the MER. Many geothermal areas are found >10 km from the nearest volcanic center, suggesting ongoing hazards associated with regional volcanism.

Distributed volcanic fields of scoria cones, maars, tuff cones and lava flows represent a crucial expression of the interplay between magmatism, tectonics and surface processes in continental rifts. We compare the cone morphology of two fields (Butajira and East Ziway) in the Main Ethiopian Rift (MER), using high-resolution digital elevation models (DEMs) to investigate volumes, surface environment and age of emplacement. Volumes of individual cones are similar in both fields (mean ~4 × 106 m3) and lower than in other distributed volcanic fields located in extensional environments. Volcanism at Butajira has created linear clusters of superimposed cones, suggesting a small number of larger (107–108 m3) fissure eruptions compared to the isolated events at East Ziway. The presence of maars and deep craters within cones at Butajira indicates phreatomagmatic activity, not seen at East Ziway where cones may have been emplaced during a dry climate phase. Shape parameters, including curvature of cone rims and ratios of cone height, width and crater depth, suggest younger eruption ages at Butajira compared to East Ziway and the possibility of ongoing activity in this area. A broader survey of cone fields across the MER using the ASTER global digital elevation model fails to identify systematic variation in height, width and volume from cone morphology, limited by low-resolution. High-resolution topography provides a useful insight into rift environments at the time of emplacement, and further surveys across the Main Ethiopian Rift may advance our understanding of distributed volcanism in extensional settings and the hazards they present.

Understanding the climate history of Mars, one of our closest planetary neighbours, has important implications for understanding the environmental evolution of Earth and other rocky planets in general. The widespread recognition of an extensive sedimentary record modified, at least in part, by liquid water, holds much promise to provide evidence about Mars’ past. However, unravelling the pressure and compositional history of Mars’ Noachian atmosphere has remained problematic. Based on expected outgassing behaviour, observed atmospheric isotope ratios, and climate models, carbon dioxide is widely considered a main constituent of the early Martian atmosphere. If this was indeed the case, it is surprising that carbonate minerals, the expected sinks for this carbon, are only abundant in a few isolated localities across the Martian surface. Three broad possibilities may account for this apparent inconsistency: (1) carbonates formed under pCO2 higher than present but were buried, or subsequently destroyed; (2) Noachian atmospheric pCO2 was significantly lower than current estimates; or (3) low temperature carbonate formation was kinetically controlled under the aqueous conditions that characterised much of the early Martian surface. While orbital spectroscopic investigations have yielded an increasing inventory of isolated carbonate-bearing deposits, their relative rarity at the near-surface has prompted suggestions that the Noachian atmosphere was commonly characterised by low pCO2. Without a more complete investigation of the carbonate-forming processes occurring within the ancient crust, no hypothesis can be tested robustly. Here, we examine the controls on Fe(II)-carbonate precipitation in low-temperature, anoxic water-rock systems as a function of pCO2. In experiments lasting up to 85 days, no measurable Fe(II)- carbonate precipitation occurred within the limits of analytical detection, despite significant and sustained supersaturation with respect to siderite. These observations are quantitatively consistent with recent investigations highlighting a significant supersaturation threshold for Fe(II)-carbonate nucleation. Reaction path models that incorporate these constraints indicate that Fe(II)-carbonate supersaturation thresholds would have been commonly met in low water:rock ratio systems isolated from the Noachian atmosphere as opposed to high water:rock ratio, open systems exposed at the near surface. These results suggest the rarity of carbonates exposed at or near the surface of Mars may be controlled, at least in part, by a lack of deep crustal exposures and lack of the geochemical conditions conducive to carbonate formation, rather than insufficient atmospheric pCO2. Such geochemical constraints are in turn consistent with available orbital geological data indicating that carbonates may be more abundant within the deep crust, potentially representing a significant subsurface carbon sink.

Restless silicic calderas present major geological hazards, and yet many also host significant untapped geothermal resources. In East Africa, this poses a major challenge, although the calderas are largely unmonitored their geothermal resources could provide substantial economic benefits to the region. Understanding what causes unrest at these volcanoes is vital for weighing up the opportunities against the potential risks. Here we bring together new field and remote sensing observations to evaluate causes of ground deformation at Aluto, a restless silicic volcano located in the Main Ethiopian Rift (MER). Interferometric Synthetic Aperture Radar (InSAR) data reveal the temporal and spatial characteristics of a ground deformation episode that took place between 2008 and 2010. Deformation time series reveal pulses of accelerating uplift that transition to gradual long-term subsidence, and analytical models support inflation source depths of ∼5 km. Gases escaping along the major fault zone of Aluto show high CO2 flux, and a clear magmatic carbon signature (CO2-δ13C of −4.2‰ to −4.5‰). This provides compelling evidence that the magmatic and hydrothermal reservoirs of the complex are physically connected. We suggest that a coupled magmatic-hydrothermal system can explain the uplift-subsidence signals. We hypothesize that magmatic fluid injection and/or intrusion in the cap of the magmatic reservoir drives edifice-wide inflation while subsequent deflation is related to magmatic degassing and depressurization of the hydrothermal system. These new constraints on the plumbing of Aluto yield important insights into the behavior of rift volcanic systems and will be crucial for interpreting future patterns of unrest.

The timing and processes that govern the end of volcanic eruptions are not yet fully understood, and there currently exists no systematic definition for the end of a volcanic eruption. Currently, end of eruption is established either by generic criteria (typically 90 days after the end of visual signals of eruption) or criteria specific to a given volcano. We explore the application of supervised machine learning classification methods: Support Vector Machine, Logistic Regression, Random Forest and Gaussian Process Classifiers and define a decisiveness index D to evaluate the consistency of the classifications obtained by these models. We apply these methods to seismic time series from two volcanoes chosen because they display contrasting styles of eruption: Telica (Nicaragua) and Nevado del Ruiz (Colombia). We find that, for both volcanic systems, the end-date we obtain by classification of seismic data is 2–4 months later than end-dates defined by the last occurrence of visual eruption (such as ash emission). This finding is in agreement with previous, general definitions of eruption end and is consistent across models. Our classifications have a higher correspondence of eruptive activity with visual activity than with database records of eruption start and end. We analyze the relative importance of the different features of seismic activity used in our models (e.g. peak event amplitude, daily event counts) and find little consistency between the two volcanic systems in terms of the most important features which determine whether activity is eruptive or non-eruptive. These initial results look promising and our approach may offer a robust tool to help determine when an eruption has ended in the absence of visual confirmation.

Radiative transfer models used in remote sensing and hazard assessment of volcanic ash require knowledge of ash optical parameters. Here, we characterise the bulk and glass compositions of a representative suite of volcanic ash samples with known complex refractive indices (n + ik: where n is the real and k is the imaginary part). Using a linear regression model, we develop a new parameterization allowing the complex refractive index of volcanic ash to be estimated from ash SiO2 content or ratio of non-bridging oxygens to tetrahedrally-coordinated cations (NBO/T). At visible wavelengths, n correlates better with bulk than glass composition (both SiO2 and NBO/T), and k correlates better with SiO2 content than NBO/T. Over a broader spectral range (0.4–19 μm), bulk correlates better than glass composition, and NBO/T generally correlates better than SiO2 content for both parts of the refractive index. In order to understand the impacts of our new parameterization on satellite retrievals, we compared IASI satellite (wavelengths 3.62–15.5 μm) mass loading retrievals using our new approach with retrievals that assumed a generic (Eyjafjallajökull) ash refractive index. There are significant differences in mass loading using our calculated indices specific to ash type rather than a generic index. Where mass loadings increase, there is often improvement in retrieval quality (corresponding to cost function decrease). This new parameterization of refractive index variation with ash composition will help to improve remote sensing retrievals for the rapid identification of ash and quantitative analysis of mass loadings from satellite data on operational timescales.

This project is funded by the Natural Environment Research Council grant NE/L013932/1 (RiftVolc). Abstract For many magmatic systems, crystal compositions preserve a complex and protracted history which may be largely decoupled from their carrier melts. The crystal cargo may hold clues to the physical distribution of melt and crystals in a magma reservoir and how magmas are assembled prior to eruptions. Here we present a geochemical study of a suite of samples from three peralkaline volcanoes in the Main Ethiopian Rift. Whilst whole-rock data shows strong fractional crystallisation signatures, the trace element systematics of feldspars, and their relationship to their host glasses, reveals complexity. Alkali feldspars, particularly those erupted during caldera-forming episodes, have variable Ba concentrations, extending to high values that are not in equilibrium with the carrier liquids. Some of the feldspars are antecrysts, which we suggest are scavenged from a crystal-rich mush. The antecrysts crystallised from a Ba-enriched (more primitive) melt, before later entrainment into a Ba-depleted residual liquid. Crystal-melt segregation can occur on fast timescales in these magma reservoirs, owing to the low viscosity nature of peralkaline liquids. The separation of enough residual melt to feed a crystal-poor post-caldera rhyolitic eruption may take as little as months to tens of years (much shorter than typical repose periods of 300-400 years). Our observations are consistent with these magmatic systems spending significant portions of their life cycle dominated by crystalline mushes containing ephemeral, small (

Satellite remote sensing is a valuable method for detecting and quantifying sulfur dioxide (SO2) emissions at volcanoes. The use of ultraviolet satellite instruments for monitoring purposes has been assessed in numerous studies, but there are advantages to using infrared measurements, including that they can operate at night and during high-latitude winters. This study focuses on the Infrared Atmospheric Sounding Interferometer (IASI). Retrievals developed for this instrument have been shown to be successful when applied to large eruptions, but little has been done to explore their potential for detecting and quantifying emissions from smaller and lower altitude emissions or for the assessment of ongoing activity. Here a “fast” linear retrieval has been applied across the globe to detect volcanic sources of SO2. The results are dominated by emissions from explosive eruptions, but signals are also evident from weak eruptions, passive degassing, and anthropogenic activity. Ecuador and Kamchatka were selected for further study with a more processing intensive iterative retrieval which can quantify the SO2 amount. At Tungurahua in Ecuador, good agreement was seen between IASI, the Ozone Monitoring Instrument (OMI) and ground-based flux data, demonstrating that the retrieval is capable of capturing relative changes in activity. Similarly, good agreement was found between IASI and OMI in Kamchatka. In this high-latitude region, OMI is unable to operate for 3 or 4 months in each year. It is therefore suggested that IASI could be used alongside other instruments for evaluating changes in volcanic activity.

This work was funded by the Natural Environment Research Council grant NE/L013932/1 (RiftVolc) and a Boise Fund grant from the Department of Zoology, University of Oxford. The Main Ethiopian Rift (MER, ~7–9°N) is the type example of a magma-assisted continental rift. The rift axis is populated with regularly spaced silicic caldera complexes and central stratovolcanoes, interspersed with large fields of small mafic scoria cones. The recent (latest Pleistocene to Holocene) history of volcanism in the MER is poorly known, and no eruptions have occurred in the living memory of the local population. Assessment of contemporary volcanic hazards and associated risk is primarily based on the study of the most recent eruptive products, typically those emplaced within the last 10–20 ky. We integrate new and published field observations and geochemical data on tephra deposits from the main Late Quaternary volcanic centres in the central MER to assess contemporary volcanic hazards. Most central volcanoes in the MER host large mid-Pleistocene calderas, with typical diameters of 5–15 km, and associated ignimbrites of trachyte and peralkaline rhyolite composition. In contrast, post-caldera activity at most centres comprises eruptions of peralkaline rhyolitic magmas as obsidian flows, domes and pumice cones. The frequency and magnitude of events varies between individual volcanoes. Some volcanoes have predominantly erupted obsidian lava flows in their most recent post-caldera stage (Fentale), whereas other have had up to 3 moderate-scale (VEI 3–4) explosive eruptions per millennium (Aluto). At some volcanoes we find evidence for multiple large explosive eruptions (Corbetti, Bora-Baricha, Boset-Bericha) which have deposited several centimeters to meters of pumice and ash in currently densely populated regions. This new overview has important implications when assessing the present-day volcanic hazard in this rapidly developing region. Postprint

International audience; Volcanogenic halogens, in particular bromine, potentially play an important role in the ozone depletion of the atmosphere. Understanding bromine behaviour in magmas is therefore crucial to properly evaluate the contribution of volcanic eruptions to atmospheric chemistry and their environmental impact. To date, bromine partitioning between silicate melts and the gas phase is very poorly constrained, with the only relevant experimental studies limited to investigation of synthetic melt with silicic compositions. In this study, fluid/melt partitioning experiments were performed using natural silicate glasses with mafic, intermediate and silicic compositions. For each composition, experiments were run with various Br contents in the initial fluid (H2O–NaBr), at T–P conditions representative of shallow magmatic reservoirs in volcanic arc contexts (100–200 MPa, 900–1200 °C). The resulting fluid/melt partition coefficients (DBrf/m) are: 5.0 ± 0.3 at 1200 °C–100 MPa for the basalt, 9.1 ± 0.6 at 1060 °C–200 MPa for the andesite and 20.2 ± 1.2 at 900 °C–200 MPa for the rhyodacite. Our experiments show that DBrf/m increases with increasing SiO2 content of the melt (as for chlorine) and suggest that it is also sensitive to melt temperature (increase of DBrf/m with decreasing temperature). We develop a simple model to predict the S–Cl–Br degassing behaviour in mafic systems, which accounts for the variability of S–Cl–Br compositions of volcanic gases from Etna and other mafic systems, and shows that coexisting magmatic gas and melt evolve from S-rich to Cl–Br enriched (relative to S) upon increasing degree of degassing. We also report first Br contents for melt inclusions from Etna, Stromboli, Merapi and Santorini eruptions and calculate the mass of bromine available in the magma reservoir prior to the eruptions under consideration. The discrepancy that we highlight between the mass of Br in the co-existing melt and fluid prior to the Merapi 2010 eruption (433 and 73 tons, respectively) and the lack of observed BrO (from space) hints at the need to investigate further Br speciation in ‘ash-rich’ volcanic plumes. Overall, our results suggest that the Br yield into the atmosphere of cold and silicic magmas will be much larger than that from hotter and more mafic magmas.

J. Biggs, I.M.Watson, W. Hutchison, T.A. Mather and D.M. Pyle are members of the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET). This work forms a contribution to the NERC Large Grant RiftVolc (NE/L01372X/1) awarded to J. Biggs. W. Hutchison was funded by NERC studentship NE/J500045/1. I.M. Watson is part of the NASA-ASTER science team and acknowledges NASA and JAXA for the provision of data. Fumaroles are the surface manifestation of hydrothermal circulation and can be influenced by magmatic, hydrothermal, hydrological and tectonic processes. This study investigates the temporal changes in fumarole temperatures and spatial extent on Aluto, a restless volcano in the Main Ethiopian Rift (MER), in order to better understand the controls on fluid circulation and the interaction between the magmatic and hydrothermal systems. Thermal infrared (TIR) satellite images, acquired by the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) over the period of 2004 to 2016, are used to generate time series of the fumarole temperatures and areas. The thermal anomalies identified in the ASTER images coincide with known fumaroles with temperatures > 80 °C and are located on or close to fault structures, which provide a pathway for the rising fluids. Most of the fumaroles, including those along the major zone of hydrothermal upwelling, the Artu Jawe Fault Zone, have pixel-integrated temperature variations of only ~ 2 ± 1.5 °C. The exception are the Bobesa fumaroles located on a hypothesised caldera ring fault which show pixel-integrated temperature changes of up to 9 °C consistent with a delayed response of the hydrothermal system to precipitation. We conclude that fumaroles along major faults are strongly coupled to the magmatic-hydrothermal system and are relatively stable with time, whereas those along shallower structures close to the rift flank are more strongly influenced by seasonal variations in groundwater flow. The use of remote sensing data to monitor the thermal activity of Aluto provides an important contribution towards understanding the behaviour of this actively deforming volcano. This method could be used at other volcanoes around the world for monitoring and geothermal exploration. Postprint

Cyclic behaviour over a range of timescales is a well-documented feature of many dome-forming volcanoes, but has not previously been identified in high resolution seismic data from Volcan de Colima (Mexico). Using daily seismic count datasets from Volcan de Colima and Soufriere Hills volcano (Montserrat), this study explores parallels in the long-term behaviour of seismicity at two long-lived systems. Datasets are examined using multiple techniques, including Fast-Fourier Transform, Detrended Fluctuation Analysis and Probabilistic Distribution Analysis, and the comparison of results from two systems reveals interesting parallels in sub-surface processes operating at both systems. Patterns of seismicity at both systems reveal complex but broadly similar long-term temporal patterns with cycles on the order of ~ 50- to ~ 200-days. These patterns are consistent with previously published spectral analyses of SO2 flux time-series at Soufriere Hills volcano, and are attributed to variations in the movement of magma in each system. Detrended Fluctuation Analysis determined that both volcanic systems showed a systematic relationship between the number of seismic events and the relative ‘roughness’ of the time-series, and explosions at Volcan de Colima showed a 1.5–2 year cycle; neither observation has a clear explanatory mechanism. At Volcan de Colima, analysis of repose intervals between seismic events shows long-term behaviour that responds to changes in activity at the system. Similar patterns for both volcanic systems suggest a common process or processes driving the observed signal but it is not clear from these results alone what those processes may be. Further attempts to model conduit processes at each volcano must account for the similarities and differences in activity within each system. The identification of some commonalities in the patterns of behaviour during long-lived dome-forming eruptions at andesitic volcanoes provides a motivation for investigating further use of time-series analysis as a monitoring tool.

Volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1–2 day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling.

Between January 2011 and April 2012, Santorini volcano (Greece) experienced a period of unrest characterised by the onset of detectable seismicity and caldera-wide uplift. This episode of inflation represented the first sizeable intrusion of magma beneath Santorini in the past 50 years. We employ a new approach using Rn-δ C systematics to identify and quantify the source of diffuse degassing at Santorini during the period of renewed activity. Soil CO flux measurements were made across a network of sites on Nea Kameni between September 2010 and January 2012. Gas samples were collected in April and September 2011 for isotopic analysis of CO (δ C), and radon detectors were deployed during September 2011 to measure (Rn). Our results reveal a change in the pattern of degassing from the summit of the volcano (Nea Kameni) and suggest an increase in diffuse CO emissions between September 2010 and January 2012. High-CO-flux soil gas samples have δ C ∼ 0 ‰. Using this value and other evidence from the literature we conclude that these CO emissions from Santorini were a mixture between CO sourced from magma, and CO released by the thermal or metamorphic breakdown of crustal limestone. We suggest that this mixing of magmatic and crustal carbonate sources may account more broadly for the typical range of δ C values of CO (from ∼ - 4 ‰ to ∼ + 1 ‰) in diffuse volcanic and fumarole gas emissions around the Mediterranean, without the need to invoke unusual mantle source compositions. At Santorini a mixing model involving magmatic CO (with δ C of - 3 ± 2 ‰ and elevated (Rn)/CO ratios ∼ 10 - 10 Bq kg) and CO released from decarbonation of crustal limestone (with (Rn)/CO ∼ 30-300 Bq kg, and δ C of + 5 ‰) can account for the δ C and (Rn)/CO characteristics of the 'high flux' gas source. This model suggests ∼ 60 % of the carbon in the high flux deep CO end member is of magmatic origin. This combination of δ C and (Rn) measurements has potential to quantify magmatic and crustal contributions to the diffuse outgassing of CO in volcanic areas, especially those where breakdown of crustal limestone is likely to contribute significantly to the CO flux. © 2013 Elsevier B.V. All rights reserved.

Cyclical patterns of behaviour in timeseries of seismic and geodetic data at volcanoes are frequently observed during lava dome-building eruptions, and are particularly well-documented from the current eruption of the Soufriere Hills Volcano (SHV), Montserrat. However, the discontinuous nature of many SO 2 measurements often preclude the identification and quantitative analysis of cyclical patterns in degassing data. Here, using a long SO 2 timeseries from SHV, with continuous measurements since 2002, we explore for the first time degassing behaviour at a resolution comparable to that possible for seismic and deformation datasets. Timeseries analysis of flux data spanning 2002–2011 reveals that SO 2 emissions at SHV exhibit complex cyclicity, with dominant cycles evident on both multi-year and multi-week (~50 day) timescales. These cycles persist through phases of both active extrusion and eruptive pause, and show close similarities to periodic components previously identified at SHV in timeseries of seismicity, ground deformation and lava extrusion. The strength of expression or amplitude of degassing cycles, particularly on multi-week timescales, shows distinct temporal variation, and appears to correlate with the occurrence and nature of explosive activity occurring in 2002–2009. This suggests that the amplitude of surface gas flux cycles is modulated by physical conditions within the conduit. Direct quantitative comparison between seismicity, dome growth, and degassing for eruptive Phases 2 (2002–2003) and 3 (2005–2007) reveals that peaks in SO 2 flux appear to correspond broadly to enhanced lava extrusion and elevated seismicity within cycles of 30–50 days. However, time lags of 2, 4 and 7 days are observed between initial low-frequency seismic swarms and peaks in dome growth, SO 2 flux and rockfall event rate respectively. Multi-parameter correlations offer valuable insights into the controls on subsurface gas ascent, but further research is required to fully explore the contributions of permeability and overpressure, as well as other subsurface processes.

[1] A systematic survey of 3 years of L band interferometric synthetic aperture radar (InSAR) measurements of the Central American Volcanic Arc shows a striking lack of magmatic deformation. We make measurements at 20 of the 26 historically active volcanoes and demonstrate that none were deforming magmatically (2007–2010), although we do measure shallow subsidence associated with flow deposits and edifice loading at three volcanoes. The minimum detection rates for our survey, as estimated from the variance in time series of radar path delay, are relatively high due to strong variability of tropospheric water vapor. We compare the average detection threshold (2.4 cm/yr) to published InSAR measurements and show that the majority (~78%) of deformation events would have been measurable with the same level of noise as Central America. We calculate that if magmatic volcano deformation were spread evenly across historically active volcanoes worldwide, the probability of none of Central America's 26 volcanoes deforming would be < 1%. The lack of magmatic deformation in Central America may be indicative of differences in magma storage relative to other well-studied continental arcs. The high proportion of basalts that ascend directly from depth relative to andesites stored in the shallow crust may limit the potential for high magnitude deformation. Magma stored in vertically elongated reservoirs and high parental melt volatile contents that result in bubble-rich, compressible magmas at shallow depths may also reduce surface deformation. We consider the measurement and analysis of a lack of deformation at active volcanoes to be essential for realizing the potential of regional scale InSAR surveys.

Volcanic sulfate aerosol is emitted from the vents of many active volcanoes, but its origin has not yet been explained. We report the first measurements of the isotopic compositions of near-vent volcanic aerosol sulfate and use the combined sulfur and oxygen isotope systemics of the aerosol and magma at Masaya volcano, Nicaragua, to draw preliminary conclusions about the production mechanism of near-source volcanic sulfate. The sulfate aerosol does not display a significant mass-independent oxygen or sulfur isotopic signature, which suggests that primary volcanic aerosol does not contribute to the larger mass-independent anomalies found in some ambient atmospheric aerosols and as preserved in ice cores. The oxygen isotope composition of the sulfate appeared to become heavier on the particle filters with increasing amount of sample collected and suggests that the δ18O value of the sulfate aerosol is < 8‰. The sy=ulfur isotopic composition of the sulfate did not vary with sample loading on the filters and had a mean δ34S value of 7.7 ± 0.8‰, similar to that of the magma (6.6 ± 0.2‰). The low Δ17O value, the δ18O value of the magma (6.6 ± 0.3‰) and the high δ18O value of atmospheric oxygen (23.5‰) suggest that known atmospheric oxidation pathways at ambient temperatures are not the major routes of production for this sulfate. Instead the isotopic systematics of aerosol and magma are consistent with sulfate production either by high-temperature equilibrium of the magmatic gas mixture with small amounts of atmospheric oxygen or by direct emission of SO₄²⁻ from the magma.

Global arc magmatism is sustained by a continuous fluid flux that is returned to the mantle in subduction zones. Despite considerable advances in simulations of melting processes, models of arc magmatism remain incompletely tested against erupted products. Here, we show that a suite of primitive volcanic rocks from across the southern Chilean arc preserves the signature of a systematic down-slab gradient in fluid chemistry. The chemical gradient is consistent with predictions from modeling, geothermometry and experiments. We infer that increasing slab-surface temperatures cause the sub-arc slab flux to become less water-rich and increasingly dominated by hydrous melts over a distance of a few kilometers behind the arc front. This change exerts a first-order control on magma chemistry, and implies discrete melt-transport pathways through subduction zones. Our results replicate patterns in other arcs, implying common sub-arc slab-surface temperature ranges in thermally-diverse subduction zones. © 2013 American Geophysical Union. All Rights Reserved.

The major explosive eruption of Charten volcano, Chile, in May 2008 provided a rare opportunity to track the long-range dispersal and deposition of fine volcanic ash. The eruption followed ~ 10,000 years of quiescence, was the largest explosive eruption globally since Hudson, Chile, in 1991, and was the first explosive rhyolitic eruption since Novarupta, Alaska, in 1912. Field examination of distal ashfall indicates that ~1.6 x 1011 kg of ash (dense rock equivalent volume of ~0.07 km3) was deposited over ~2 x 105 km2 of Argentina during the first week of eruption. The minimum eruption magnitude, estimated from the mass of the tephra deposit, is 4.2. Several discrete ashfall units are identifiable from their distribution and grain size characteristics, with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes. Ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3-6 km. Deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption, which in this case comprised several phases over a week-long period of intense activity. Copyright 2009 by the American Geophysical Union.

Seismic activity has been postulated as a trigger of volcanic eruption on a range of timescales, but demonstrating the occurrence of triggered eruptions on timescales beyond a few days has proven difficult using global datasets. Here, we use the historic earthquake and eruption records of Chile and the Andean southern volcanic zone to investigate eruption rates following large earthquakes. We show a significant increase in eruption rate following earthquakes of MW > 8, notably in 1906 and 1960, with similar occurrences further back in the record. Eruption rates are enhanced above background levels for ~ 12 months following the 1906 and 1960 earthquakes, with the onset of 3-4 eruptions estimated to have been seismically influenced in each instance. Eruption locations suggest that these effects occur from the near-field to distances of ~ 500 km or more beyond the limits of the earthquake rupture zone. This suggests that both dynamic and static stresses associated with large earthquakes are important in eruption-triggering processes and have the potential to initiate volcanic eruption in arc settings over timescales of several months. © 2008 Elsevier B.V. All rights reserved.

Santorini Volcano, the site of the catastrophic Minoan eruption in Greece, exhibits two distinct eruptive styles: small, effusive eruptions occur relatively frequently and build shields and domes of lava, whereas large explosive eruptions occur rarely, at intervals of 10,000-30,000 years. Both types of eruption were thought to incubate in a shallow magma chamber that is continually charged by small batches of melt injected into the chamber from below. However, petrological work suggests that at least 15% of the material ejected during the Minoan explosive eruption arrived in the magma chamber less than 100 years before the eruption. Here we use Satellite Radar Interferometry (InSAR) and Global Positioning System (GPS) measurements of surface deformation at Santorini to show that 10-20 million m 3 of magma have been intruded beneath the volcano since January 2011. This volume is equivalent to 10-50% of the volumes of recorded dome-forming eruptions. GPS and triangulation data show that this is the only volumetrically significant intrusion to have occurred since 1955, shortly after the last eruption. Our observations imply that whether Santorini is in an explosive or dome-forming phase, its shallow magma chamber is charged episodically by high-flux batches of magma. The durations of these events are short in comparison with the intervening periods of repose and their timing is controlled by the dynamics of deeper magma reservoirs.

article i nfo Establishing a time series of deformation is one of the keys to understanding and predicting the magmatic behaviour of active volcanoes. Satellite techniques represent an increasingly useful tool for measuring volcanic deformation over timescales spanning days to decades. Colombia contains numerous young or active volcanoes, many of which are inaccessible. We use L-band (23.6 cm wavelength) radar data acquired between 2006 and 2009, to survey 15 active volcanoes along the Colombian segment of the Northern Volcanic Zone. Analysis of 100 interferograms showed that the majority of volcanoes were not deforming. However, independent interferograms display an average subsidence of 3 cm on the northeast flank of Galeras, coinciding with the January 2008 eruption. We combine InSAR, field measurements and source modelling to determine the origin, size and location of the source of subsidence at Galeras. Our results suggest that this signal was caused by deflation of the magma chamber associated with the January 2008 event. Modelling provides insight into the depth to source (~2 km) and a volume change (−6.5×10 5 m 3 ) which is consistent with that derived from modelling contemporaneous tilts and the volume of material erupted. Previous studies based on various datasets support the existence of a resident/recurring chamber at this location, over a decadal timescale. Our InSAR results corroborate the hypothesis of shallow magma storage beneath Galeras and provide the first piece of evidence that can be linked to a particular eruption.

Lava flows can produce changes in topography on the order of 10s-100s of metres. A knowledge of the resulting volume\ud change provides evidence about the dynamics of an eruption. We present a method to measure topographic changes from the\ud differential InSAR phase delays caused by the height differences between the current topography and a Digital Elevation Model\ud (DEM). This does not require a pre-event SAR image, so it does not rely on interferometric phase remaining coherent during\ud eruption and emplacement. Synthetic tests predicts that we can estimate lava thickness of as little as �9 m, given a minimum of 5\ud interferograms with suitably large orbital baseine separations. In the case of continuous motion, such as lava flow subsidence, we\ud invert interferometric phase simultaneously for topographic change and displacement. We demonstrate the method using data from\ud Santiaguito volcano, Guatemala, and measure increases in lava thickness of up to 140 m between 2000 and 2009, largely associated\ud with activity between 2000 and 2005. We find a mean extrusion rate of 0.43 +/- 0.06 m3/s, which lies within the error bounds of\ud the longer term extrusion rate between 1922-2000. The thickest and youngest parts of the flow deposit were shown to be subsiding\ud at an average rate of �-6 cm/yr. This is the first time that flow thickness and subsidence have been measured simultaneously. We\ud expect this method to be suitable for measurment of landslides and other mass flow deposits as well as lava flows.

Volcanic lightning, perhaps the most spectacular consequence of the electrification of volcanic plumes, has been implicated in the origin of life on Earth, and may also exist in other planetary atmospheres. Recent years have seen volcanic lightning detection used as part of a portfolio of developing techniques to monitor volcanic eruptions. Remote sensing measurement techniques have been used to monitor volcanic lightning, but surface observations of the atmospheric electric Potential Gradient (PG) and the charge carried on volcanic ash also show that many volcanic plumes, whilst not sufficiently electrified to produce lightning, have detectable electrification exceeding that of their surrounding environment. Electrification has only been observed associated with ash-rich explosive plumes, but there is little evidence that the composition of the ash is critical to its occurrence. Different conceptual theories for charge generation and separation in volcanic plumes have been developed to explain the disparate observations obtained, but the ash fragmentation mechanism appears to be a key parameter. It is unclear which mechanisms or combinations of electrification mechanisms dominate in different circumstances. Electrostatic forces play an important role in modulating the dry fall-out of ash from a volcanic plume. Beyond the local electrification of plumes, the higher stratospheric particle concentrations following a large explosive eruption may affect the global atmospheric electrical circuit. It is possible that this might present another, if minor, way by which large volcanic eruptions affect global climate. The direct hazard of volcanic lightning to communities is generally low compared to other aspects of volcanic activity. © Springer Science+Business Media B.V. 2006.

[1] Direct-sampling and remote-sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d < 10 μm) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d ∼ 1.15 μm. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emission flux of fine silicate particles was estimated as ∼1011 s-1, equivalent to ∼55 kg d-1. Sun photometry, aerosol spectrometry, and thermal precipitation were used to determine the overall particle size distribution of the plume (0.01 < d(μm) < 10). Sun photometry and aerosol spectrometry measurements indicate the presence of a large number of particles (assumed to be aqueous) with d ∼ 1 μm. Aerosol spectrometry measurements further show an increase in particle size as the nighttime approached. The emission flux of particles from Masaya was estimated as ∼1017 s-1, equivalent to ∼5.5 Mg d-1 where d < 4 μm. Copyright 2009 by the American Geophysical Union.

We report measurements of Hg, SO2, and halogens (HCl, HBr, HI) in volcanic gases from Masaya volcano, Nicaragua, and gaseous SO2 and halogens from Telica volcano, Nicaragua. Mercury measurements were made with a Lumex 915+ portable mercury vapor analyzer and gold traps, while halogens, CO2 and S species were monitored with a portable multi gas sensor and filter packs. Lumex Hg concentrations in the plume were consistently above background and ranged up to 350 ng m-3. Hg/SO2 mass ratios measured with the real-time instruments ranged from 1.1 × 10-7 to 3.5 × 10-5 (mean 2 × 10-5). Total gaseous mercury (TGM) concentrations measured by gold trap ranged from 100 to 225 ng m-3. Reactive gaseous mercury accounted for 1% of TGM, while particulate mercury was 5% of the TGM. Field measurements of Masaya's SO2 flux, combined with the Hg/SO2 ratio, indicate a Hg flux from Masaya of 7.2 Mg a-1. At Masaya's low temperature famaroles, Hg/CO2 mass ratios were consistently around 2 × 10-8, lower than observed in the main vent (Hg/C02 ∼ 10-7). Low-temperature fumarole Hg fluxes from Masaya are insignificant (∼150 g a-1). Ratios of S, C and halogen species were also measured at Masaya and Telica volcanoes. CO2/ SO2 ratios at Masaya ranged from 2.8 to 3.9, comparable to previously published values. At Masaya molar Br/SO2 was 3 × 10-4 and I/SO2 was 2 × 10-5, suggesting fluxes of 0.2-0.5 Mg HBr d-1 and 0.02-0.05 Mg HI d-1. At Telica the Br/SO2 ratio was also 3 × 10-4 and the I/SO2 ratio was 5.8 × 10-5, with corresponding fluxes of 0.2 Mg HBr d-1 and 0.06 Mg HI d-1. Gases at both volcanoes are enriched in I relative to Br and Cl, compared to gases from volcanoes elsewhere. Copyright 2008 by the American Geophysical Union.

Analyses of air, water and vegetation samples collected in June 2008 offer new insights into the environmental effects of the May 2008 Chaitén eruption on Argentina, which was subject to significant ashfall between 42°S and 46°S. Results from air filtration in the ash-affected town of Esquel (with samples analysed by gravimetry and scanning electron microscopy) show the total mass of resuspended ash in the air is well-correlated with traffic activity. However, this variation is primarily related to varying amounts of the largest particles, with little variation in the amounts of fine ash particles (i.e., d < 4 μm). This result suggests that the hazard associated with resuspended ash remains high even when traffic activity is low and the air is not visibly dusty. We estimate PM2.5 ∼ 200 μg m- 3, PM4 ∼ 300 μg m- 3 and PM10 ∼ 1000 μg m- 3; these concentrations far exceed WHO air quality guidelines and likely persisted for several months. Results from water and vegetation sampling (with samples analysed by inductively coupled plasma mass spectrometry and ion chromatography) indicate that ashfall resulted in significant compositional changes in ephemeral lakes and coirón grass (Festuca pallescens). For B, Cd, Zn, Tl, Cu and Ni, there are strong linear correlations between concentrations and ash thickness (where > 2 mm) in both datasets. These results suggest that the eruption of Chaitén led to significant changes in the concentrations of trace volatile elements within the environment. Analysis of vegetation samples collected in January 2009 indicates that the elevated element concentrations in coirón grass persisted for < 8 months. These results offer insights into the environmental fate of volatile trace elements emitted during volcanic eruptions. © 2009 Elsevier B.V. All rights reserved.

Here we report results from a multidisciplinary field campaign at Villarrica volcano, Chile, in March 2009. A range of direct sampling and remote sensing techniques was employed to assess gas and aerosol emissions from the volcano, and extend the time series of measurements that have been made during recent years. Airborne traverses beneath the plume with an ultraviolet spectrometer yielded an average SO2 flux of 3.7kg s-1. This value is similar to previous measurements made at Villarrica during periods of quiescent activity. The composition of the plume was measured at the crater rim using electrochemical sensors and, for the first time, open-path Fourier transform infrared spectroscopy, yielding a composition of 90.5mol% H2O, 5.7% CO2, 2.6% SO2, 0.9% HCl, 0.3% HF and

The silicic dome complex of Santiaguito, Guatemala, has exhibited continuous extrusive activity for 90 years. Despite its longevity, remarkably little is known about the magmatic plumbing system beneath Santiaguito. Here, we use petrological analyses of lava samples to define this plumbing system, from storage in the lower to mid-crust through to extrusion onto the surface. Magmatic storage conditions are constrained using amphibole and plagioclase phenocrysts; ascent processes are examined using the breakdown rims of amphibole phenocrysts and the texture and composition of groundmass, while shallow processes are revealed by the alteration of titanomagnetites and matrix glass. Santiaguito magmas contain amphiboles that formed from ~ 24 km to ~ 12 km beneath the surface, with temperatures of ~ 940 to ~ 980 °C, and f O2 of NNO + 0.4 to NNO + 1.2. Amphibole breakdown rims suggest that during the final phases of ascent, magma may rise from ~ 12 km (the limit of amphibole stability) relatively rapidly (~ 27 to ~ 84 m h − 1 ). We infer from the texture of the groundmass that melt rigidifies prior to extrusion — a finding that may have important consequences for conduit dynamics.

Sweet chestnut leaves (Castanea sativa) collected from the flanks of Mt Etna volcano in 2005-2007 were analysed by inductively-coupled plasma mass spectrometry to investigate the spatial and temporal variability of element concentrations. The aim of this work was to determine whether these leaves are a bio-indicator for volcanic gas, aerosol and ash deposition and to gain new insights into the environmental effects of quiescent and eruptive volcanic plumes. Results show a positive correlation between sample variability in the concentration of elements in Castanea sativa and enrichment factors of elements in the plume. The spatial and temporal variability of chalcophilic elements (As, Cd, Cu, Mo, Tl, Zn) is consistent with prevailing winds transporting eruptive plumes to the south-east of the summit, resulting in enhanced plume deposition onto the flanks of the volcano. Similar spatial and temporal variability was found for the halide-forming elements (Cs, K, Rb) and intermediate elements (Al, Co, Mn). The spatial variability of chalcophilic, intermediate and halide-forming elements during quiescent periods was diminished (relative to eruptive periods) and could not be explained by plume deposition. In contrast, the concentrations of lithophilic elements (Ba, Ca, Mg, Sr) did not show any clear spatial variability even during eruptive periods. Comparisons between enrichment factors for elements in Castanea sativa and literature values for enrichment factors of the volcanic plume, groundwater and lichen were made. Whilst Castanea sativa offers insights into the spatial and temporal variability of deposition, the species may not be a bio-indicator for plume composition due to biological fractionation. © 2008 Elsevier B.V. All rights reserved.

The 2014–2015 Bárðarbunga-Veiðivötn fissure eruption at Holuhraun produced about 1.5 km3 of lava, making it the largest eruption in Iceland in more than 200 years. Over the course of the eruption, daily volcanic sulfur dioxide (SO2) emissions exceeded daily SO2 emissions from all anthropogenic sources in Europe in 2010 by at least a factor of 3. We present surface air quality observations from across Northern Europe together with satellite remote sensing data and model simulations of volcanic SO2 for September 2014. We show that volcanic SO2 was transported in the lowermost troposphere over long distances and detected by air quality monitoring stations up to 2750 km away from the source. Using retrievals from the Ozone Monitoring Instrument (OMI) and the Infrared Atmospheric Sounding Interferometer (IASI), we calculate an average daily SO2 mass burden of 99 ± 49 kilotons (kt) of SO2 from OMI and 61 ± 18 kt of SO2 from IASI for September 2014. This volcanic burden is at least a factor of 2 greater than the average SO2 mass burden between 2007 and 2009 due to anthropogenic emissions from the whole of Europe. Combining the observational data with model simulations using the United Kingdom Met Office's Numerical Atmospheric-dispersion Modelling Environment model, we are able to constrain SO2 emission rates to up to 120 kilotons per day (kt/d) during early September 2014, followed by a decrease to 20–60 kt/d between 6 and 22 September 2014, followed by a renewed increase to 60–120 kt/d until the end of September 2014. Based on these fluxes, we estimate that the eruption emitted a total of 2.0 ± 0.6 Tg of SO2 during September 2014, in good agreement with ground-based remote sensing and petrological estimates. Although satellite-derived and model-simulated vertical column densities of SO2 agree well, the model simulations are biased low by up to a factor of 8 when compared to surface observations of volcanic SO2 on 6–7 September 2014 in Ireland. These biases are mainly due to relatively small horizontal and vertical positional errors in the simulations of the volcanic plume occurring over transport distances of thousands of kilometers. Although the volcanic air pollution episodes were transient and lava-dominated volcanic eruptions are sporadic events, the observations suggest that (i) during an eruption, volcanic SO2 measurements should be assimilated for near real-time air quality forecasting and (ii) existing air quality monitoring networks should be retained or extended to monitor SO2 and other volcanic pollutants., School of Earth and Environment (University of Leeds) UK Natural Environment Research Council (NERC) NE/I015612/1 Met Office Academic Partnership NERC NE/M021130/1 COMET

This paper presents a new tool, AshCalc, for the comparison of the three most commonly used models for the calculation of the bulk volume of volcanic tephra fall deposits: the exponential model, the power law model and the Weibull model. AshCalc provides a simple and intuitive tool to speed up the analysis of tephra deposits and compare and contrast the fits for each model. Two improvements in terms of computational performance are implemented in AshCalc for the estimation of the parameters for the Weibull model. The first is an analytic method for reducing the number of free parameters, whilst the second exaggerates the minima in parameter space, leading to a more robust solution. We show that AshCalc provides volume estimates in line with other previously published estimates and hence can be used with a high degree of confidence. We include the open source python code for Ashcalc with the intention that it can be used both as a stand-alone program and integrated into other python projects.

Understanding the underlying structure of data from volcano monitoring is essential to identify precursors to changes in eruptive activity and to comprehend volcanic processes. However, effective analysis of longer-term trends in these signals is challenging as volcanic data are not necessarily statistically stationary or linear, particularly those from lava dome-forming volcanoes, which are commonly characterised by pulsatory eruptive activity. Here, we use detrended fluctuation analysis (DFA), a statistical technique previously applied to nonstationary data, to identify long-range (slowly decaying, e.g. power-law) correlations in a number of time-series of volcano seismicity recorded during the recent dome-forming eruptions of Volcán de Colima, Mexico, and Soufrière Hills Volcano, Montserrat. For all the time-series analysed, correlation strength varies through time and/or on different timescales; in some cases, this variation is periodic, seasonal, and/or related to activity. These results may provide new insights into eruptive processes and possibly further constrain the generation mechanisms of a number of the volcano-seismic event classes analysed. Furthermore, the correlation properties of real-time seismic measurements are shown (retrospectively) to contain information valuable to real-time volcano monitoring that is not identifiable by conventional analysis techniques. This study therefore demonstrates that long-range correlation analysis may be useful for extracting additional information from monitoring data at dome-forming or similar volcanoes. © 2013 Elsevier B.V.

One of the longest continuous periods of dome-forming activity on record is the ongoing eruption of Santiaguito, Guatemala. Dome-building began in 1922, within the crater formed during the cataclysmic 1902 eruption of Santa Maria, and continues today. The earliest erupted Santiaguito lavas are chemically and mineralogically identical to the dacite pumice erupted in 1902. The erupted magma has become progressively less evolved over time, with a decrease in whole rock SiO 2 from ~ 66 to ~ 62 wt.% from 1922 to 2002. New geochemical data from Santiaguito are consistent with a model of magma being extracted progressively from a chemically-stratified lower crustal (~ 12 to ~ 25 km) storage zone thought to have formed during the ~ 25 ka of quiescence that preceded the 1902 eruption. The bimodal distribution of plagioclase phenocryst core compositions in early Santiaguito lavas suggests that they were strongly influenced by magma mixing in addition to fractional crystallization. However, lavas erupted since the 1940s show a unimodal distribution, suggesting a diminishing role for mixing within the Santiaguito system. Trace element data suggest that the decrease in silica content over time is best explained by a decrease in the extent of fractional crystallization of ~ 15% over the 80 years covered by our sample set.

We report the first satellite-based survey of volcanic sulphur dioxide (SO2) degassing in Papua New Guinea, using Ozone Monitoring Instrument (OMI) data. OMI is sensitive to low-level passive degassing. These observations are useful for volcano monitoring, hazard assessment (particularly aviation hazard) and assessment of arc geochemical budgets and are of immense value in remote regions with little ground-based instrumentation, such as Papua New Guinea. We identify Bagana, Manam, Rabaul, Ulawun and Langila as the active sources of volcanic SO2 in Papua New Guinea, with Bagana being the largest source. We present an OMI SO2 time series for 2005–2008 and a total detected regional output of ∼1.8 × 109 kg SO2. About 40% of emissions were released by major eruption events at Manam (January 2005), Bagana (June 2006) and Rabaul (October 2006). Over the past century however, we estimate that major explosive eruptions contribute

The edifice of a volcano is a unique deformational environment, dependent not just on active volcanic processes but also on its composition, structure, and morphology. We measured the deformation of Volcan Arenal, Costa Rica, using interferograms constructed from both ALOS and RadarSat data between 2005 and 2009. The volcano's western flanks are moving downslope at an angle of ∼55° below the horizontal plane and a consistent rate of at least ∼7 cm/yr. We use the pattern, rate, and direction of motion to test several hypotheses for its origin. Our favored explanation is creep along a shallow sliding plane, most likely the interface between deposits postdating the 1968 lateral blast eruption and the older lavas and paleosoils beneath. Our measurement of slope movement adds to a small set of rate measurements for gravity-driven deformation at volcanoes and is distinctive in both its relatively high rate and shallow origin. Observation of deformation at Arenal contributes both to the assessment of particular hazards around Arenal itself and, more generally, to the study of the stability of young stratovolcanoes.

We present results from a campaign in March 2009 to assess the current state of emissions from Masaya Volcano, Nicaragua. These results constitute one of the most comprehensive inventories to date of emissions from an active volcano and update the exceptional record of emissions from Masaya. Results from open-path Fourier transform infrared spectroscopy and filter packs demonstrate that, in terms of H2O, SO2, CO2, HCl, and HF (molar H2O/SO2 = 63, CO2/SO2 = 2.7, SO2/HCl = 1.7, SO2/HF = 8.8), the 2009 gas composition was highly comparable to that from the 1998 to 2000 period, indicating stability of the shallow magma system. This continuity extends to certain aerosol species (molar SO2/SO42- = 190, Na+/SO 42- = 0.68, K+/SO42- = 0.71, Ca2+/SO42- = 1.6 × 10-2, Mg2+/SO42- = 3.6 × 10-3) and, to a lesser extent, the heavy halogens (i.e., molar HCl/HBr = 2.4 × 103, HCl/HI = 5.0 × 104). In contrast to an earlier study at Masaya, we did not detect HNO3. SO2 fluxes were low (690 Mg d-1), suggesting that Masaya was close to the minimum of its degassing cycle. By combining compositional results with the SO2 flux, we estimate a total volatile flux of 14,000 Mg d-1. This rate is consistent with 1-4 wt% volatile loss from a convective magma flux of 17,000-4000 kg s-1. These results will allow for a better understanding of degassing processes at Masaya and other basaltic volcanoes. Copyright 2010 by the American Geophysical Union.

[1] Persistent, open-vent degassing of Erebus volcano, Antarctica, is a significant point source of gases and aerosol to the austral polar troposphere. We report here on the chemical composition and size distribution of the Erebus aerosol, focusing on the water-soluble fraction. The aerosol was sampled at the rim of the active crater using a cascade impactor, which collected and sized particles in 14 size bins from >10 to 0.01 μm. The soluble fraction of the Erebus aerosol is distinct from other volcanic sources in several respects. It is dominated by chloride-bearing particles (over 30% of total mass) and has an unusually high Cl−/SO42− molar ratio of 3.5. Coarse particles contribute little to the total mass of the soluble fraction. Elevated concentrations of F−, Cl−, Br−, and SO42− are found in a narrow particle size fraction of 0.1–0.25 μm. The detection of particulate Br− reinforces our understanding of the potential for quiescent volcanic emissions to deplete tropospheric ozone. The small aerosol size reflects the low atmospheric temperature and humidity, which inhibit particle growth. Halide-alkali metal salts (Na, K)(Cl, F) appear to be the most abundant species in the aerosol. The concentration of Pb is high compared to other volcanoes; its exsolution may be promoted by the high abundance of halogens in Erebus magma. Despite the previously reported high NOx content in the plume, we did not detect significant quantities of nitrate in the near-vent aerosol. Our findings emphasize the potential regional significance of emissions from Erebus for understanding the Antarctic atmospheric composition and glaciochemical records.

article i nfo Article history: Received 6 August 2009 Accepted 4 January 2010 Available online xxxx Biomagnetic monitoring, using tree leaves as passive surfaces for particle collection, has been shown to be a promising technique for assessing the dispersion and deposition of particles in the context of anthropogenic pollution. By comparing leaves' magnetic properties with trace metal levels measured in the leaves, we here assess the utility of the biomagnetic technique as a sensitive, fast and inexpensive method for assessment of volcanic plume deposition. Samples of sweet chestnut leaves (Castanea sativa) were collected from the area surrounding Mt. Etna volcano in Sicily during the 2008 growing season when the volcano was displaying mild eruptive activity. Previous work has shown that the trace metal concentrations of these leaves show promise as a bio-indicator of volcanic gas, aerosol and ash deposition on the flanks of Mt. Etna. For 2008, ICP- MS analysis of the elemental abundances within the leaves showed that As, Cd, Cu, Mo, Tl, K, B, Al and Co displayed elevated concentrations downwind of the volcanic source, to the E-ESE, but with overall reduced concentrations relative to 2007. Less explosive activity than 2007 and a broader, more easterly wind field may have distributed the volcanic plume over a wider area, both of which would account for reduced trace element concentrations in 2008. Correspondence of elevated concentrations in both years (2007 and 2008) with their respective wind fields suggests that plume deposition is the controlling factor rather than variability in the soils and that these leaves do indeed have potential as bio-indicators of the plume's dispersion. Magnetic analysis of the leaves shows that the spatial distribution of saturation isothermal remanent magnetisation (SIRM) and magnetic susceptibility (χlf) values display a strong correlation with the wind-influenced plume transport direction for 2008, with elevated concentrations of magnetic minerals on the eastern flanks, in broad agreement with the ICP-MS data. This spatial distribution provides further evidence of plume variability as the main control on the concentrations of magnetic particles on the leaf surfaces and on elemental uptake by the tree and suggests that biomagnetic monitoring may also hold promise as a method of assessing the dispersion and impacts of volcanic plumes. The dominant magnetic mineral on the leaf surfaces is a magnetite-like mineral (contributing >90% of the SIRM), of coarse, multi- domain (MD) grain size (∼ 5t o 15 μm). A volcanogenic source is most likely, as magnetites from anthropogenic sources are typically an order of magnitude smaller in grain size (∼0.1-1 μm). These new results from the use of environmental magnetism on leaves, in a volcanically-affected region, suggest that biomagnetic monitoring offers a new, sensitive and rapid means for the assessment of volcanic plume deposition over wide areas.

Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes were measured across an extended size range (10 nm < d < 100 μm) using a combination of techniques. Automated scanning electron microscopy (QEMSCAN) was used to chemically analyze many thousands of insoluble particles (collected on pumped filters) allowing the relationships between particle size, shape, and composition to be investigated. The size distribution of fine silicate particles (d < 10 μm) was found to be lognormal, consistent with formation by bursting of gas bubbles at the surface of the magma. The compositions of fine silicate particles were found to vary between magmatic and nearly pure silica; this is consistent with depletion of metal ions by reactions in the acidic environment of the gas plume and vent. Measurements of the size, shape and composition of fine silicate particles may potentially offer insights into preemission, synemission, and postemission processes. The mass flux of fine silicate particles from Mt. Etna released during noneruptive volcanic degassing in 2004 and 2005 was estimated to be ∼7000 kg d-1. Analysis of particles in the range 0.1 < d/μm < 100 by ion chromatography shows that there are persistent differences in the size distributions of sulfate aerosols between the two main summit plumes. Analysis of particles in the range 0.01 μm < d < 0.1 μm by scanning transmission electron microscopy (STEM) shows that there are significant levels of nanoparticles in the Mt. Etna plumes although their compositions remain uncertain. Copyright 2008 by the American Geophysical Union.

Although the negative impacts of volcanism on society are well documented and accepted, many possible benefits from volcanoes are not always fully considered. This paper provides suggestions for understanding and implementing volcanoes' benefits by suggesting further application of existing risk management frameworks to volcanology: living with risk by using the sustainable livelihoods approach at the local level. This paper presents an overview bringing established paradigms into volcanic risk management where they are sometimes absent despite their advantages. The sustainable livelihoods approach is important in its application to volcanic scenarios in four ways:(i)Understanding, communicating, and managing vulnerability and risk and local perceptions of vulnerability and risk beyond immediate threats to life.(ii)Maximising the benefits to communities of their volcanic environment, especially during quiescent periods, without increasing vulnerability.(iii)Managing crises.(iv)Managing reconstruction and resettlement after a crisis. An overview of case studies is provided showing how volcanic opportunities could be used for sustainable livelihoods. The approach of living with volcanic risks and benefits could be adopted and implemented as an integral part of changing perceptions of volcanoes and of managing volcano-related crisis and non-crisis situations. However, the sustainable livelihoods approach is not a panacea, so limitations are discussed along with why living near a volcano cannot solve all livelihood concerns. In particular, livelihood diversity and livelihood transferability to other locations assists in living with volcanoes. © 2007 Elsevier B.V. All rights reserved.

Measuring Hg/SO2 ratios in volcanic emissions is essential for better apportioning the volcanic contribution to the global Hg atmospheric cycle. Here, we report the first real-time simultaneous measurement of Hg and SO2 in a volcanic plume, based on Lumex and MultiGAS techniques, respectively. We demonstrate that the use of these novel techniques allows the measurements of Hg/SO2 ratios with a far better time resolution than possible with more conventional methods. The Hg/SO2 ratio in the plume of FO fumarole on La Fossa Crater, Vulcano Island spanned an order of magnitude over a 30 minute monitoring period, but was on average in qualitative agreement with the Hg/SO2 ratio directly measured in the fumarole (mean plume and fumarole ratios being 1.09 × 10-6 and 2.9 × 10-6, respectively). The factor 2 difference between plume and fumarole compositions provides evidence for fast Hg chemical processing, the plume. Copyright 2007 by the American Geophysical Union.