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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.

There is a temporal correlation between the peak activity of the North Atlantic Igneous Province (NAIP) and the Paleocene–Eocene Thermal Maximum (PETM), suggesting that the NAIP may have initiated and/or prolonged this extreme warming event. However, corroborating a causal relationship is hampered by a scarcity of expanded sedimentary records that contain both climatic and volcanic proxies. One locality hosting such a record is Fur Island in Denmark, where an expanded pre- to post-PETM succession containing hundreds of NAIP ash layers is exceptionally well preserved. We compiled a range of environmental proxies, including mercury (Hg) anomalies, paleotemperature proxies, and lithium (Li) and osmium (Os) isotopes, to trace NAIP activity, hydrological changes, weathering, and seawater connectivity across this interval. Volcanic proxies suggest that NAIP activity was elevated before the PETM and appears to have peaked during the body of the δ13C excursion, but decreased considerably during the PETM recovery. This suggests that the acme in NAIP activity, dominated by flood basalt volcanism and thermogenic degassing from contact metamorphism, was likely confined to just ~200 kyr (ca. 56.0–55.8 Ma). The hundreds of thick basaltic ashes in the post-PETM strata likely represent a change from effusive to explosive activity, rather than an increase in NAIP activity. Detrital δ7Li values and clay abundances suggest that volcanic ash production increased basaltic reactive surface area, likely enhancing silicate weathering and atmospheric carbon sequestration in the early Eocene. Signals in lipid biomarkers and Os isotopes, traditionally used to trace paleotemperature and weathering changes, are used here to track seaway connectivity. These proxies indicate that the North Sea was rapidly cut off from the North Atlantic in under 12 kyr during the PETM recovery due to NAIP thermal uplift. Our findings reinforce the hypothesis that the emplacement of the NAIP had a profound and complex impact on Paleocene–Eocene climate, both directly through volcanic and thermogenic degassing, and indirectly by driving regional uplift and changing seaway connectivity.

Satellite instruments play a valuable role in detecting, monitoring and characterising emissions of ash and gas into the atmosphere during volcanic eruptions. Plumes of ash and sulfur dioxide (SO2) from the April 2021 eruption of La Soufrière volcano on St Vincent in the Eastern Caribbean were observed by a multiple satellite instruments. This study looks at these plumes with two satellite instruments: the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite (GOES), and the Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp platforms. Using true and false colour images, and brightness temperature difference images produced from the ABI data, a minimum of 32 eruptive events were identified. The ABI images were used to determine the approximate start and end times and character of each event. In this way the eruption has been divided into four phases: (1) an initial explosive event, (2) a sustained event lasting over nine hours, (3) a pulsatory phase with 23 explosive events in a 54 hour period and (4) a waning sequence of explosive events. The IASI instrument was used to study the dispersion of SO2 from this eruption. The results showed a highly complex structure to the plume, in terms of the column amounts and height, which is likely linked to the multiple explosive events. The SO2 is shown to have largely been emitted between 13 and 19 km. This was primarily in the upper troposphere and around the height of the tropopause, but with some emission into the stratosphere. The SO2 was transported around the globe with parts of the plume reaching as far as 45° S and 45° N. The largest SO2 atmospheric burden measured with IASI was 0.31±0.09 Tg, recorded on the 13 April 2021 (descending orbits). The SO2 masses were converted into fluxes. The SO2 flux was shown to peak on 10 April and then shown to decrease over time. By summing the IASI SO2 flux results, it is estimated that a total of 0.57±0.44 Tg of SO2 was emitted to the atmosphere. However, due to the limitations associated with the retrieval this should be considered a minimum estimate of the total mass of SO2 emitted. An average e-folding time of 7.09±5.70 days was computed based on the IASI SO2 results: similar to other tropical eruptions of this magnitude. There are a number of similarities between the 1979 and 2021 eruptions at La Soufrière. For example, both eruptions consisted of a series of explosive events with varied heights including some emission into the stratosphere. The similarities between the 1979 and 2021 highlight the importance of studying these eruptions to be prepared for future activity.

Past large igneous province (LIP) emplacement is commonly associated with mantle plume upwelling and led to major carbon emissions. One of Earth’s largest past environmental perturbations, the Toarcian oceanic anoxic event (T-OAE; ~183 Ma), has been linked to Karoo-Ferrar LIP emplacement. However, the role of mantle plumes in controlling the onset and timing of LIP magmatism is poorly understood. Using global plate reconstruction models and Lower Toarcian sedimentary mercury (Hg) concentrations, we demonstrate (i) that the T-OAE occurred coevally with Karoo-Ferrar emplacement and (ii) that timing and duration of LIP emplacement was governed by reduced Pangean plate motion, associated with a reversal in plate movement direction. This new model mechanistically links Earth’s interior and surficial processes, and the mechanism is consistent with the timing of several of the largest LIP volcanic events throughout Earth history and, thus, the timing of many of Earth’s past global climate change and mass extinction events.

The latest Permian mass extinction (LPME) was triggered by magmatism of the Siberian Traps Large Igneous Province (STLIP), which left an extensive record of sedimentary Hg anomalies at Northern Hemisphere and tropical sites. Here, we present Hg records from terrestrial sites in southern Pangea, nearly antipodal to contemporaneous STLIP activity, providing insights into the global distribution of volcanogenic Hg during this event and its environmental processing. These profiles (two from Karoo Basin, South Africa; two from Sydney Basin, Australia) exhibit significant Hg enrichments within the uppermost Permian extinction interval as well as positive Δ

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.

Volcanic activity associated with the emplacement of Large Igneous Provinces (LIPs) has been linked to most Phanerozoic extinctions/episodes of major environmental change. In recent years, mercury (Hg) enrichments and elevated mercury/total organic carbon (Hg/TOC) ratios have been increasingly utilized as a marker of volcanism in sedimentary records deposited distally from LIPs. The proxy is based on the premise that volcanism is a major natural source of the element to the atmosphere, and that it was especially important prior to anthropogenic emissions. To date, end-Permian and end-Triassic records illustrate the strongest use of Hg as a marker of volcanic activity, supplemented by the use of Hg isotopes and other evidence for LIP eruptions and volatile emissions. Sedimentary records of several other events also document Hg enrichments in at least one region, suggestive of a regional- or global-scale perturbation to the Hg cycle at those times, potentially linked to volcanism. The Cenomanian– Turonian Oceanic Anoxic Event 2 appears to be the exception, with strata documenting peaks in Hg/TOC in a small minority of studied records, suggesting that there was only a minimal perturbation to the Hg cycle at that time. Even for events where a global Hg-cycle perturbation apparently occurred, varying Hg enrichments documented from individual archives of the same event indicate that the complex biogeochemical cycling of mercury can result in a strong influence of local/regional aquatic, biological, or sedimentary processes on the precise signature of any worldwide disturbance. Of additional intrigue is an apparent lack of correlation of Hg and Hg/TOC with other volcanic proxies such as osmium isotopes, suggesting that the two systems record different aspects of LIP volcanism and emplacement. Recent studies are beginning to investigate these above complexities, but further work is needed to fully explore the nuances of Hg in the geological record, and how it can be best employed as a proxy for LIP volcanism.

This study was supported by the Leverhulme Trust grant 2016–21 (Nature and impacts of Middle Pleistocene volcanism in the Ethiopian Rift). KF was supported by the UK's Natural Environment Research Council (NERC) grant NE/L013932/1 (RiftVolc: The Past, Present and Future of Rift Volcanism in the Main Ethiopian Rift), a Boise Fund grant from the Department of Zoology, University of Oxford, and acknowledges Fonds de Recherche Scientifique – FNRS MIS grant F.4515.20. Tephra work on the Chew Bahir cores in the Cambridge Tephra Lab by AA, AP and CL was made possible by NERC grant NE/K014560/1. Ar–Ar dating was supported by grants NIGFSC IP-1683-1116 and IP-1680-1116. The iCRAG lab is supported by SFI 13/RC/2092. The Main Ethiopian Rift (MER) is renowned as a focus of investigations into human origins. It is also the site of many large volcanic calderas, whose eruptions have spanned the timeframe of speciation, cultural innovation, and dispersal of our species. Yet, despite their significance for dating human fossils and cultural materials, the timing and geochemical signatures of some of the largest eruptions have remained poorly constrained at best. Here, through a programme of field surveys, geochemical analysis and 40Ar/39Ar dating, we report the ages of MER ignimbrites and link them to widespread tephra layers found in sequences of archaeological and paleoenvironmental significance. We date major eruptions of Fentale (76 ± 18 ka), Shala (ca. 145–155 ka), Kone (184 ± 42 ka and ca. 200 ± 12 ka) and Gedemsa (251 ± 47 ka) volcanoes, and correlate a suite of regionally important tephra horizons. Geochemical analysis highlights the predominantly peralkaline rhyolitic melt compositions (7.5–12 wt% Na2O + K2O, 70–76 wt% SiO2) across the central MER and remarkable similarity in incompatible trace element ratios, limiting the correlation of deposits via glass composition alone. However, by integrating stratigraphic and geochronological evidence from proximal deposits, lake sediment cores and distal outcrops at archaeological sites, we have traced ash layers associated with the ca. 177 ka Corbetti, ca. 145–155 ka Shala and ca. 108 ka Bora-Baricha-Tullu-Moye eruptions across southern Ethiopia. In addition to strengthening the tephrochronological framework that supports paleoenvironmental and archaeological work in the region, our findings have wider implications for evaluating the hypothesis of a middle Pleistocene ‘ignimbrite flare-up’ in the MER, and for evaluating the impacts of these great eruptions on landscapes, hydrology, and human ecology. Publisher PDF

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.

The 6-month-long 2014–2015 Holuhraun eruption was the largest in Iceland for 200 years, emitting huge quantities of sulfur dioxide (SO2) into the troposphere, at times overwhelming European anthropogenic emissions. Weather, terrain and latitude made continuous ground-based or UV satellite sensor measurements challenging. Infrared Atmospheric Sounding Interferometer (IASI) data are used to derive the first time series of daily SO2 mass present in the atmosphere and its vertical distribution over the entire eruption period. A new optimal estimation scheme is used to calculate daily SO2 fluxes and average e-folding time every 12 h. For the 6 months studied, the SO2 flux was observed to be up to 200 kt day−1 and the minimum total SO2 erupted mass was 4.4±0.8 Tg. The average SO2 e-folding time was 2.4±0.6 days. Where comparisons are possible, these results broadly agree with ground-based near-source measurements, independent remote-sensing data and values obtained from model simulations from a previous paper. The results highlight the importance of using high-resolution time series data to accurately estimate volcanic SO2 emissions. The SO2 mass missed due to thermal contrast is estimated to be of the order of 3 % of the total emission when compared to measurements by the Ozone Monitoring Instrument. A statistical correction for cloud based on the AVHRR cloud-CCI data set suggested that the SO2 mass missed due to cloud cover could be significant, up to a factor of 2 for the plume within the first kilometre from the vent. Applying this correction results in a total erupted mass of 6.7±0.4 Tg and little change in average e-folding time. The data set derived can be used for comparisons to other ground- and satellite-based measurements and to petrological estimates of the SO2 flux. It could also be used to initialise climate model simulations, helping to better quantify the environmental and climatic impacts of future Icelandic fissure eruptions and simulations of past large-scale flood lava eruptions.

Long-lived basaltic volcanic eruptions are a globally important source of environmentally reactive, volatile metal pollutant elements such as selenium, cadmium and lead. The 2018 eruption of Kīlauea, Hawai’i produced exceptionally high discharge of metal pollutants, and was an unprecedented opportunity to track them from vent to deposition. Here we show, through geochemical sampling of the plume that volatile metal pollutants were depleted in the plume up to 100 times faster than refractory species, such as magnesium and iron. We propose that this rapid wet deposition of complexes containing reactive and potentially toxic volatile metal pollutants may disproportionately impact localised areas close to the vent. We infer that the relationship between volatility and solubility is an important control on the atmospheric behaviour of elements. We suggest that assessment of hazards from volcanic emissions should account for heterogeneous plume depletion of metal pollutants. Volatile metal pollutants in basaltic volcanic plumes can be deposited up to 100 times faster than refractory species, and may produce disproportionate impacts at proximal locations, according to extensive sampling of Kīlauea’s 2018 eruption plume.

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.

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

Episodes of large igneous province (LIP) volcanism punctuate Earth history. LIPs are anomalous geologically rapid large‐volume accumulations of igneous rock on the Earth’s surface and in the shallow crust. Periods of LIP emplacement are often temporally associated with times of profound environmental and climatic change throughout Earth history, particularly during the last 300 million years. The fluxes of gas and particles emitted during LIP volcanism are key candidates for triggering these Earth system responses. Understanding these events, their feedbacks and impacts on the Earth system requires collaboration between the fields of volcanology, atmospheric science, ocean chemistry, sedimentology and palaeobiology amongst other fields. This presentation will explore how evidence of the environmental impacts of LIP volcanism and the processes leading to these effects is best combined often from disparate sources including: (1) temporal associations between the dates or proxies of LIPs and evidence of environmental change captured in the geological record; (2) historical records or monitoring studies of the effects of large‐scale recent volcanic activity such as the Laki eruption in 1783–1784 CE and its deposits; and (3) scaling up from observations and measurements of the environmental impacts of present‐day volcanism such as the 2014–2015 Holuhraun eruption and the 2018 Lower East Rift Zone eruption at Kīlauea, Hawai‘i. Recent progress in each of these areas sets the scene for future advances in our understanding of these profoundly important events in Earth’s history.

The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state., The Paleocene–Eocene boundary coincided with runaway global warming possibly analogous to future climate change, but the sources of greenhouse gasses have remained unresolved. Here, the authors reveal volcanism triggered initial warming, and subsequent carbon was released after crossing a tipping point.

Mercury (Hg) is increasingly being used as a sedimentary tracer of Large Igneous Province (LIP) volcanism, and supports hypotheses of a coincidence between the formation of several LIPs and episodes of mass extinction and major environmental perturbation. However, numerous important questions remain to be answered before Hg can be claimed as an unequivocal fingerprint of LIP volcanism, as well as an understanding of why some sedimentary records document clear Hg enrichment signals whilst others do not. Of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle, as well as the role played by depositional processes in recording global Hg-cycle perturbations. Here, new mercury records of Cretaceous Oceanic Anoxic Event 2 (OAE 2: ∼94 Ma) and the latest Cretaceous (∼67–66.0 Ma) are presented. OAE 2 is associated with the emplacement of multiple, predominantly submarine, LIPs; the latest Cretaceous with subaerial volcanism of the Deccan Traps. Both of these connections are strongly supported by previously published trends towards unradiogenic osmium- (Os) isotope values in globally distributed sedimentary records. Hg data from both events show considerable variation between different locations, attributed to the effectiveness of different sediment types in registering the Hg signal, with lithologically homogeneous records documenting more clear Hg enrichments than sections with major changes in lithology such as limestones to claystones or organic-rich shales. Crucially, there is no geographically consistent signal of sedimentary Hg enrichment in stratigraphic records of either OAE 2 or the latest Cretaceous that matches Os-isotope evidence for LIP emplacement, indicating that volcanism did not cause a global Hg perturbation throughout the entire eruptive history of the LIPs formed at those times. It is suggested that the discrepancy between Os-isotope and Hg trends in records of OAE 2 is caused by the limited dispersal range of Hg emitted from submarine volcanoes compared to the global-scale distribution of Os. A similar lack of correlation between these two proxies in uppermost Cretaceous strata indicates that, although subaerial volcanism can perturb the global Hg cycle, not all subaerial eruptions will do so. These results highlight the variable impact of different volcanogenic processes on the efficiency of Hg dispersal across the globe. Factors that could influence the impact of LIP eruptions on the global mercury cycle include submarine versus subaerial volcanism, volcanic intensity or explosivity, and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic-rich sediments.

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.

International audience; Measuring the low bromine abundances in Earth’s materials remains an important challenge in order to constrain the geodynamical cycle of this element. Suitable standard materials are therefore required to establish reliable analytical methods to quantify Br abundances. In this study we characterise 21 Br-doped glasses synthesized from natural volcanic rocks of mafic to silicic compositions, in order to produce a new set of standards for Br analyses using various techniques. The nominal Br contents (amounts of Br loaded in the experimental samples) of 15 of 21 glasses were confirmed within 20% by instrumental neutron activation analysis (INAA). Using this new set of standards, we compare three micro-analytical approaches to measure Br contents in silicate glasses: synchrotron X-ray fluorescence (SR-XRF), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), and secondary ion mass spectrometry (SIMS). With SR-XRF, the Br contents of the standard glasses were determined with the highest accuracy (< 10% for Br ≥ 10 ppm; > 25% for Br ≤ 5 ppm), and high precision (< 10% for Br contents > 10 ppm; 20-30% for Br ≤ 10 ppm). The detection limit was estimated to be less than 1 ppm Br. All those factors combined with a high spatial resolution (5x5 μm for the presented measurements), means that SR-XRF is well suited to determine the low Br abundance in natural volcanic glasses (crystal-hosted melt inclusions or matrix glasses of crystallized samples). At its current stage of development, the LA-ICP-MS method allows the measurement of hundreds to thousands ppm Br in silicate glasses with a precision and accuracy generally within 20 %. The Br detection limit of this method has not been estimated but its low spatial resolution (90 μm) currently prevents its use to characterise natural volcanic glasses, however it is fully appropriate to analyse super liquidus or sparsely phyric, Br-rich experimental charges. Our study shows that SIMS appears to be a promising technique to measure the low Br contents of natural volcanic glasses. Its spatial resolution is relatively good (~ 15 μm) and, similarly to SR-XRF, the detection limit is estimated to be ≤ 1 ppm. Using our new set of standards, the Br contents of two MPI-DING reference glasses containing less than 1.2 ppm of Br were reproduced with precision < 5% and accuracy < 20%. Moreover, SIMS presents the advantage of being a more accessible instrument than SR-XRF and data processing is more straightforward.

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.

Magmas from continental arcs built on thick crust have elevated incompatible element abundances and “enriched” radiogenic isotope ratios compared to magmas erupted in island and continental arcs overlying thinner crust. The relative influence of the slab, mantle, and upper plate on this variability is heavily debated. The Andean Southern Volcanic Zone (SVZ; 33–46°S) is an ideal setting to investigate the production of enriched continental arc compositions, because both crustal thickness and magma chemistry vary coherently along strike. However, the scarcity of primitive magmas in the thick-crusted northern SVZ has hindered previous regional studies. To better address the origin of enriched continental compositions, we investigate the geochemistry (major and trace element abundances, 87Sr/86Sr and 143Nd/144Nd ratios) of new mafic samples from Don Casimiro and Maipo volcanoes within the Diamante-Maipo Caldera Complex of the northern SVZ. While evolved Diamante-Maipo samples show evidence for crustal assimilation, the trace element and isotopic enrichment of the most mafic samples cannot result from crustal processing, as no known regional or global basement lithologies are enriched in all of the necessary incompatible trace elements. Subduction erosion models similarly fail to account for the enriched isotopic and trace element signature of these samples. Instead, we suggest that the enrichment of northern SVZ magmas is derived from an enriched ambient mantle component (similar to EM1-type ocean island basalts), superimposed on a northward decline in melt extent. A substantial, but nearly uniform contribution of melts from subducting sediment and altered oceanic crust are required at all latitudes. The EM1-like enrichment may arise from recycling of metasomatized subcontinental lithospheric mantle (M-SCLM), as the isotopic trajectory of primitive rear-arc monogenetic cones trend towards the compositions of SCLM melts sampled across South America. Isotopic data from spatially distributed rear-arc centres demonstrate that the arc-parallel variations in the degree of EM1-type enrichment observed in arc-front samples are also present up to 600 km behind the trench in the rear-arc. Rear-arc trace element systematics require significant but variable quantities of slab melts to be transported to the mantle wedge at these large trench distances. Overall, we show that a unified model incorporating variable mantle enrichment, slab additions, and melt extents can account for along and across-arc trends within the SVZ. The recognition that mantle enrichment plays a key role in the production of enriched continental compositions in the SVZ has important implications for our understanding of the chemical evolution of the Earth. If ambient mantle enrichment is not taken into account, petrogenetic models of evolved lavas may overestimate the role of crustal assimilation, which, in turn, may lead models of continental crust growth to overestimate the amount of continental material that has been recycled back into the mantle.

Santorini Volcano is an outstanding natural laboratory for studying arc volcanism, having had twelve Plinian eruptions over the last 350,000 years, at least four of which caused caldera collapse. Periods between Plinian eruptions are characterized by intra-caldera edifice construction and lower intensity explosive activity. The Plinian eruptions are fed from magma reservoirs at 4–8 km depth that are assembled over several centuries prior to eruption by the arrival of high-flux magma pulses from deeper in the sub-caldera reservoir. Unrest in 2011–2012 involved intrusion of two magma pulses at about 4 km depth, suggesting that the behaviour of the modern-day volcano is similar to the behaviour of the volcano prior to Plinian eruptions. Emerging understanding of Santorini's plumbing system will enable better risk mitigation at this highly hazardous volcano.

As our ability to detect volcanic unrest improves, we are increasingly confronted with the question of whether the unrest has a magmatic origin (magma on the move) or a non-magmatic origin from a change in the hydrothermal system (fluids that are not magma on the move) or tectonic processes. The cause of unrest has critical implications for the potential eruptive hazard (e.g. used in constructing Bayesian Event Trees), but is frequently the subject of debate, even at well-studied systems. Here, we propose a set of multi-disciplinary observations and numerical models that could be used to evaluate conceptual models about the cause of unrest. These include measurements of gas fluxes and compositions and the isotopic signature of some components (e.g. H 2 , He, C, SO 2 , H 2 O , CH 4 and CO 2 ), the spatial and temporal characteristics of ground deformation, thermal output, seismicity, changes in gravity, and whether there is topographic uplift or subsidence spanning hundreds to thousands of years. In several volcanic systems, both magmatic and non-magmatic unrest is occurring at the same time. While none of these observations or models is diagnostic on its own, we illustrate several examples where they have been used together to make a plausible conceptual model of one or more episodes of unrest and whether eruptions did or did not follow the unrest. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

Ash clouds are a geographically far reaching hazard associated with volcanic eruptions. To minimise the risk that these pose to aircraft and to limit disruption to the aviation industry, it is important to closely monitor the emission and atmospheric dispersion of these plumes. The altitude of the plume is an important consideration and is an essential input into many models of ash cloud propagation. CO2 slicing is an established technique for obtaining the top height of meteorological clouds and previous studies have demonstrated that there is potential for this method to be used for volcanic ash. In this study, the CO2 slicing technique has been adapted for volcanic ash and applied to spectra obtained from the Infrared Atmospheric Sounding Interferometer (IASI). Simulated ash spectra are first used to select the most appropriate channels and then demonstrate that the technique has merit for determining the altitude of the ash. These results indicate a strong match between the true heights and CO2 slicing output with a root mean square error (RMSE) of less than 800 m. Following this, the technique was applied to spectra obtained with IASI during the Eyjafjallajökull and Grimsvötn eruptions in 2010 and 2011 respectively, both of which emitted ash clouds into the troposphere, and which have been extensively studied with satellite imagery. The CO2 slicing results were compared against those from an optimal estimation scheme, also developed for IASI, and a satellite borne LiDAR is used for validation. Overall, the CO2 slicing tool performs better than the optimal estimation scheme. The CO2 slicing heights returned a RMSE value of 2.2 km when compared against the LiDAR. This is lower than the RMSE for the optimal estimation scheme (2.8 km). The CO2 slicing technique is a relatively fast tool and the results suggest that this method could be used to get a first approximation of the ash cloud height, potentially for use for hazard mitigation, or as an input for other retrieval techniques or models of ash cloud propagation.

Structure-from-motion (SfM) photogrammetry techniques are now widely available to generate digital terrain models (DTMs) from optical imagery, providing an alternative to costlier options such as LiDAR or satellite surveys. SfM could be a useful tool in hazard studies because its minimal cost makes it accessible even in developing regions and its speed of use can provide updated data rapidly in hazard-prone regions. Our study is designed to assess whether crowd-sourced SfM data is comparable to an industry standard LiDAR dataset, demonstrating potential real-world use of SfM if employed for disaster risk reduction purposes. Three groups with variable SfM knowledge utilized 16 different camera models, including four camera phones, to collect 1001 total photos in one hour of data collection. Datasets collected by each group were processed using VisualSFM, and the point densities, accuracies and distributions of points in the resultant point clouds (DTM skeletons) were compared. Our results show that the point clouds are resilient to inconsistency in users’ SfM knowledge: crowd-sourced data collected by a moderately informed general public yields topography results comparable in data density and accuracy to those produced with data collected by highly-informed SfM users or experts using LiDAR. This means that in a real-world scenario involving participants with a diverse range of expertise, topography models could be produced from crowd-sourced data quite rapidly and to a very high standard. This could be beneficial to disaster risk reduction as a relatively quick, simple and low-cost method to attain rapidly updated knowledge of terrain attributes, useful for the prediction and mitigation of many natural hazards.

International audience; Large igneous province (LIP) volcanism has been proposed as a key trigger of several major climate and environmental perturbations during the Phanerozoic Aeon. Large-scale carbon emissions associated with one or both of magmatic degassing from the Greater Ontong-Java Plateau (G-OJP) and intrusion of organic-rich sediments by High Arctic LIP (HALIP) sills have been widely suggested as the trigger of the Early Aptian Oceanic Anoxic Event (OAE 1a: ~120 Ma). However, the respective roles of the two LIPs and associated carbon sources in causing this crisis remain debated. Here, six records of OAE 1a from the Pacific, Tethyan, Arctic, and South Atlantic realms are investigated, combining mercury (Hg) concentrations and osmium- (Os-) isotope ratios as proxies of LIP activity. Together with previously published datasets, the results indicate globally consistent Os-isotope evidence for LIP activity during OAE 1a, but geographically variable stratigraphic Hg trends. Clear mercury enrichments that match Os-isotope evidence of LIP activity, and suggest a Hg-cycle perturbation during the onset of OAE 1a, are documented at one Pacific site extremely proximal to the G-OJP, but not in Arctic, Tethyan or Atlantic records. This pattern highlights significant G-OJP volcanism during the onset of OAE 1a, and re-emphasises the limited potential for submarine LIP eruptions to cause Hg-cycle perturbations except in areas very proximal to source. The absence of clear Hg peaks in basal OAE 1a strata from the Arctic (or anywhere outside of the Pacific) does not support intense HALIP activity at that time, suggesting that the G-OJP was the more volcanically active LIP when OAE 1a commenced. Thus, G-OJP emissions of mantle carbon were more likely to have played a major role in initiating OAE 1a than thermogenic volatiles associated with the HALIP. A transient pulse of HALIP-related subaerial eruptions and/or thermogenic volatile emissions during the early–middle part of OAE 1a, potentially evidenced by more widespread Hg enrichments in strata from that time (including in the Arctic), might have prolonged the event. However, a non-volcanic cause of these later Hg influxes cannot be excluded. These findings challenge previous suggestions that magmatic CO2 emissions from LIPs were incapable of causing major carbon-cycle perturbations alone, and highlight the need for further investigations to establish whether the high volume/emplacement rate of the G-OJP (potentially an order of magnitude greater than other LIPs) made it a unique case that stands in contrast to other provinces where the role of thermogenic volatiles was likely more crucial.

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.