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Explosive volcanism is a key contributor to climate variability on interannual to centennial timescales1. Understanding the far-field societal impacts of eruption-forced climatic changes requires firm event chronologies and reliable estimates of both the burden and altitude (that is, tropospheric versus stratospheric) of volcanic sulfate aerosol2,3. However, despite progress in ice-core dating, uncertainties remain in these key factors4. This particularly hinders investigation of the role of large, temporally clustered eruptions during the High Medieval Period (HMP, 1100–1300 ce), which have been implicated in the transition from the warm Medieval Climate Anomaly to the Little Ice Age5. Here we shed new light on explosive volcanism during the HMP, drawing on analysis of contemporary reports of total lunar eclipses, from which we derive a time series of stratospheric turbidity. By combining this new record with aerosol model simulations and tree-ring-based climate proxies, we refine the estimated dates of five notable eruptions and associate each with stratospheric aerosol veils. Five further eruptions, including one responsible for high sulfur deposition over Greenland circa 1182 ce, affected only the troposphere and had muted climatic consequences. Our findings offer support for further investigation of the decadal-scale to centennial-scale climate response to volcanic eruptions.

The Eldgjá eruption is the largest basalt lava flood of the Common Era. It has been linked to a major ice‐core sulfur (S) spike in 939–940 CE and Northern Hemisphere summer cooling in 940 CE. Despite its magnitude and potential climate impacts, uncertainties remain concerning the eruption timeline, atmospheric dispersal of emitted volatiles, and coincident volcanism in Iceland and elsewhere. Here, we present a comprehensive analysis of Greenland ice‐cores from 936 to 943 CE, revealing a complex volatile record and cryptotephra with numerous geochemical populations. Transitional alkali basalt tephra matching Eldgjá are found in 939–940 CE, while tholeiitic basalt shards present in 936/937 CE and 940/941 CE are compatible with contemporaneous Icelandic eruptions from Grímsvötn and Bárðarbunga‐Veiðivötn systems (including V‐Sv tephra). We also find four silicic tephra populations, one of which we link to the Jala Pumice of Ceboruco (Mexico) at 941 ± 1 CE. Triple S isotopes, Δ33S, spanning 936–940 CE are indicative of upper tropospheric/lower stratospheric transport of aerosol sourced from the Icelandic fissure eruptions. However, anomalous Δ33S (down to −0.4‰) in 940–941 CE evidence stratospheric aerosol transport consistent with summer surface cooling revealed by tree‐ring reconstructions. Tephra associated with the anomalous Δ33S have a variety of compositions, complicating the attribution of climate cooling to Eldgjá alone. Nevertheless, our study confirms a major S emission from Eldgjá in 939–940 CE and implicates Eldgjá and a cluster of eruptions as triggers of summer cooling, severe winters, and privations in ∼940 CE. The eruption of Eldgjá in the tenth century is the largest lava flood in the history of Iceland. Although Eldgjá emitted immense volumes of ash, lava, and gas, the exact timing and duration of this eruption, as well as its environmental and climatic impact remain unclear. Here, we provide a comprehensive chemical analysis of Greenland ice‐core records spanning the period 936–943 CE. We identify volcanic ash from at least three different Icelandic eruptions and confirm that there was a major ash and gas emission from Eldgjá in 939 CE. Using tree ring temperature estimates we find strong evidence for Northern Hemisphere climate cooling in the summer of 940 CE. However, the variety of volcanic ash identified in the ice‐cores shows that several Icelandic and Northern Hemisphere arc volcanoes were also erupting in this period. While Eldgjá remains the prime candidate, these additional eruptions complicate the attribution of reported climate and societal changes to Eldgjá alone. Ultimately, our study sheds new light on a cluster of volcanic eruptions between 936 and 943 CE and highlights the challenges of disentangling the individual contributions of multiple eruptions on the environment and climate. New analyses of Greenland ice‐core records of volcanism between 936 and 943 CEIcelandic eruptions from Grímsvötn and Bárðarbunga‐Veiðivötn detected between 936 and 941 CE, and major Eldgjá emission in 939–940 CEVarious silicic eruptions identified, including the Jala Pumice (Mexico), providing new and valuable trans‐continental tephra isochrons New analyses of Greenland ice‐core records of volcanism between 936 and 943 CE Icelandic eruptions from Grímsvötn and Bárðarbunga‐Veiðivötn detected between 936 and 941 CE, and major Eldgjá emission in 939–940 CE Various silicic eruptions identified, including the Jala Pumice (Mexico), providing new and valuable trans‐continental tephra isochrons

Recent Icelandic rifting events have illuminated the roles of centralized crustal magma reservoirs and lateral magma transport1–4, important characteristics of mid-ocean ridge magmatism1,5. A consequence of such shallow crustal processing of magmas4,5is the overprinting of signatures that trace the origin, evolution and transport of melts in the uppermost mantle and lowermost crust6,7. Here we present unique insights into processes occurring in this zone from integrated petrologic and geochemical studies of the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula in Iceland. Geochemical analyses of basalts erupted during the first 50 days of the eruption, combined with associated gas emissions, reveal direct sourcing from a near-Moho magma storage zone. Geochemical proxies, which signify different mantle compositions and melting conditions, changed at a rate unparalleled for individual basaltic eruptions globally. Initially, the erupted lava was dominated by melts sourced from the shallowest mantle but over the following three weeks became increasingly dominated by magmas generated at a greater depth. This exceptionally rapid trend in erupted compositions provides an unprecedented temporal record of magma mixing that filters the mantle signal, consistent with processing in near-Moho melt lenses containing 107–108m3of basaltic magma. Exposing previously inaccessible parts of this key magma processing zone to near-real-time investigations provides new insights into the timescales and operational mode of basaltic magma systems.

Millions of people are potentially exposed to volcanic gases worldwide, and exposures may differ from those in anthropogenic air pollution. A systematic literature review found few primary studies relating to health hazards of volcanic gases. S[O.sub.2] and acid aerosols from eruptions and degassing events were associated with respiratory morbidity and mortality but not childhood asthma prevalence or lung function decrements. Accumulations of [H.sub.2]S and COs from volcanic and geothermal sources have caused fatalities from asphyxiation. Chronic exposure to [H.sub.2]S in geothermal areas was associated with increases in nervous system and respiratory diseases. Some impacts were on a large scale, affecting several countries (e.g., Laki fissure eruption in Iceland in 1783-4). No studies on health effects of volcanic releases of halogen gases or metal vapors were located. More high quality collaborative studies involving volcanologists and epidemiologists are recommended., AT LEAST 455 million people worldwide live within potential exposure range of a volcano that has been active within recorded history. (1) Volcanoes and geothermal areas are associated with emissions [...]

Today, volcanic sulfur emissions into the atmosphere are measured spectroscopically from the ground, air and space. For eruptions prior to the satellite era, two main sulfur proxies are used, the rock and ice core records, as illustrated by Peccia et al. (2023, https://doi.org/10.1029/2023gl103334). The first approach is based on calculations of the sulfur content of the magma, while the second uses traces of sulfur deposited in ice. Both approaches have their limitations. For glaciochemistry, the volcano responsible for a sulfur anomaly is often unknown and the atmospheric pathway by which the sulfur reached the ice uncertain. The petrologic method relies, too, on uncertain estimates of eruption size and a number of geochemical assumptions that are hard to verify. A deeper knowledge of processes occurring both within magma bodies prior to eruption, and within volcanic plumes in the atmosphere is needed to further our understanding of the impacts of volcanism on climate. Volcanic emissions of sulfur gases during large eruptions can change the global climate. Today, advanced spectroscopic tools allow us to measure sulfur from the ground, air and space. But to understand the impacts of volcanic activity on climate back through history we need to estimate volcanic sulfur releases in other ways. Clues can be found in the pumice deposits found around a volcano and, perhaps more surprisingly, in the ice caps of the polar regions, which receive the eventual fallout from large eruptions. Both approaches have limitations that are addressed in a recent work by Peccia et al. (2023, https://doi.org/10.1029/2023gl103334) and that are at the focus of our commentary. The impact of volcanic activity on climate remains difficult to quantify for eruptions prior to the instrumental eraThe petrological and glaciochemical methods each provide answers, but are still fraught with large uncertaintiesWe need to further our understanding of the physicochemical processes occurring both within magma reservoirs and volcanic plumes The impact of volcanic activity on climate remains difficult to quantify for eruptions prior to the instrumental era The petrological and glaciochemical methods each provide answers, but are still fraught with large uncertainties We need to further our understanding of the physicochemical processes occurring both within magma reservoirs and volcanic plumes

Efforts to date the oldest modern human fossils in eastern Africa, from Omo-Kibish1–3and Herto4,5in Ethiopia, have drawn on a variety of chronometric evidence, including 40Ar/39Ar ages of stratigraphically associated tuffs. The ages that are generally reported for these fossils are around 197 thousand years (kyr) for the Kibish Omo I3,6,7, and around 160–155 kyr for the Herto hominins5,8. However, the stratigraphic relationships and tephra correlations that underpin these estimates have been challenged6,8. Here we report geochemical analyses that link the Kamoya’s Hominid Site (KHS) Tuff9, which conclusively overlies the member of the Omo-Kibish Formation that contains Omo I, with a major explosive eruption of Shala volcano in the Main Ethiopian Rift. By dating the proximal deposits of this eruption, we obtain a new minimum age for the Omo fossils of 233 ± 22 kyr. Contrary to previous arguments6,8, we also show that the KHS Tuff does not correlate with another widespread tephra layer, the Waidedo Vitric Tuff, and therefore cannot anchor a minimum age for the Herto fossils. Shifting the age of the oldest known Homo sapiensfossils in eastern Africa to before around 200 thousand years ago is consistent with independent evidence for greater antiquity of the modern human lineage10.

The Laacher See eruption (LSE) in Germany ranks among Europe’s largest volcanic events of the Upper Pleistocene1,2. Although tephra deposits of the LSE represent an important isochron for the synchronization of proxy archives at the Late Glacial to Early Holocene transition3, uncertainty in the age of the eruption has prevailed4. Here we present dendrochronological and radiocarbon measurements of subfossil trees that were buried by pyroclastic deposits that firmly date the LSE to 13,006 ± 9 calibrated years before present (bp; taken as ad1950), which is more than a century earlier than previously accepted. The revised age of the LSE necessarily shifts the chronology of European varved lakes5,6relative to the Greenland ice core record, thereby dating the onset of the Younger Dryas to 12,807 ± 12 calibrated years bp, which is around 130 years earlier than thought. Our results synchronize the onset of the Younger Dryas across the North Atlantic–European sector, preclude a direct link between the LSE and Greenland Stadial-1 cooling7, and suggest a large-scale common mechanism of a weakened Atlantic Meridional Overturning Circulation under warming conditions8–10.

China has a rich record of Holocene volcanism that is relatively little known outside the country. It is encountered in large stratovolcanoes in the NE, linked to subduction of the Pacific plate (e.g. Changbaishan), in smaller volcanoes on the Tibetan margin, associated with the collision of India and Eurasia (e.g. Tengchong, Ashishan), and in more isolated centres, possibly resulting from mantle upwelling (e.g. volcanoes in Hainan island). This makes China a natural laboratory for studies of intraplate volcanism, and significant progress in understanding its nature and origins has been made over the past quarter century. Here, we introduce the first publication in English to provide a comprehensive survey of the state of knowledge and research highlights. Accordingly, we provide an overview of the dynamics, geology, geochemistry, volcanic histories and geophysical studies of 14 volcanic areas associated with the Holocene documented thus far. The special publication represents a benchmark reference on the topic but, as importantly, we hope that it will stimulate new, international collaborations aimed at deepening our understanding of the origins, history, hazards and associated risks of China's volcanoes.

Discusses the use of remote sensing satellites in monitoring volcanic activity. Limitations of traditional monitoring methods; Conversion of infrared measurements into a `model' surface temperature; Quantitative insights into the thermal physics of volcanic processes; Estimation of sea surface temperatures; Analysis of Lonquimay volcano in the southern Andes of Chile; Support of the two-component model. INSET: Landsat's thematic mapper..

Gas bubbles form as magmas ascend in the crust and exsolve volatiles. These bubbles evolve chemically and physically as magma decompression and crystallization proceed. It is generally assumed that the gas remains in thermal equilibrium with the melt but the relationship between gas and melt redox state is debated. Here, using absorption spectroscopy, we report the composition of gases emitted from the lava lake of Kīlauea Volcano, Hawaii, and calculate equilibrium conditions for the gas emissions. Our observations span a transition between more and less vigorous-degassing regimes. They reveal a temperature range of up to 250 °C, and progressive oxidation of the gas, relative to solid rock buffers, with decreasing gas temperature. We suggest that these phenomena are the result of changing gas bubble size. We find that even for more viscous magmas, fast-rising bubbles can cool adiabatically, and lose the redox signature of their associated melts. This process can result in rapid changes in the abundances of redox-sensitive gas species. Gas composition is monitored at many volcanoes in support of hazard assessment but time averaging of observations can mask such variability arising from the dynamics of degassing. In addition, the observed redox decoupling between gas and melt calls for caution in using lava chemistry to infer the composition of associated volcanic gases. The redox state of volcanic gases and melts can become decoupled during magma ascent, according to observations of gas emissions from Kīlauea’s lava lake, Hawaii. Cooling of fast-rising bubbles changes the abundance of redox-sensitive gas species.

The eruption of Samalas in Indonesia in 1257 ranks among the largest sulfur-rich eruptions of the Common Era with sulfur deposition in ice cores reaching twice the volume of the Tambora eruption in 1815. Sedimentological analyses of deposits confirm the exceptional size of the event, which had both an eruption magnitude and a volcanic explosivity index of 7. During the Samalas eruption, more than 40 km3of dense magma was expelled and the eruption column is estimated to have reached altitudes of 43 km. However, the climatic response to the Samalas event is debated since climate model simulations generally predict a stronger and more prolonged surface air cooling of Northern Hemisphere summers than inferred from tree-ring-based temperature reconstructions. Here, we draw on historical archives, ice-core data and tree-ring records to reconstruct the spatial and temporal climate response to the Samalas eruption. We find that 1258 and 1259 experienced some of the coldest Northern Hemisphere summers of the past millennium. However, cooling across the Northern Hemisphere was spatially heterogeneous. Western Europe, Siberia and Japan experienced strong cooling, coinciding with warmer-than-average conditions over Alaska and northern Canada. We suggest that in North America, volcanic radiative forcing was modulated by a positive phase of the El Niño–Southern Oscillation. Contemporary records attest to severe famines in England and Japan, but these began prior to the eruption. We conclude that the Samalas eruption aggravated existing crises, but did not trigger the famines.

Explosive volcanism can alter global climate, and hence trigger economic, political and demographic change. The climatic impact of the largest volcanic events has been assessed in numerous modelling studies and tree-ring-based hemispheric temperature reconstructions. However, volcanic surface cooling derived from climate model simulations is systematically much stronger than the cooling seen in tree-ring-based proxies, suggesting that the proxies underestimate cooling; and/or the modelled forcing is unrealistically high. Here, we present summer temperature reconstructions for the Northern Hemisphere from tree-ring width and maximum latewood density over the past 1,500 years. We also simulate the climate effects of two large eruptions, in AD 1257 and 1815, using a climate model that accounts explicitly for self-limiting aerosol microphysical processes. Our tree-ring reconstructions show greater cooling than reconstructions with lower spatial coverage and based on tree-ring width alone, whereas our simulations show less cooling than previous simulations relying on poorly constrained eruption seasons and excluding nonlinear aerosol microphysics. Our tree-ring reconstructions and climate simulations are in agreement, with a mean Northern Hemisphere extra-tropical summer cooling over land of 0.8 to 1.3 °C for these eruptions. This reconciliation of proxy and model evidence paves the way to improved assessment of the role of both past and future volcanism in climate forcing.

Recent advances in infrared laser spectroscopy may enable scientists to make accurate, in situ, real-time measurements of the isotopic composition of gas species emitted from volcanoes.

Abstract: The correlation spectrometer (COSPEC), the principal tool for remote measurements of volcanic SO2, is rapidly being replaced by low-cost, miniature, ultraviolet (UV) spectrometers. We compared two of these new systems with a COSPEC by measuring SO2 column amounts at Kīlauea Volcano, Hawaii. The two systems, one calibrated using in-situ SO2 cells, and the other using a calibrated laboratory reference spectrum, employ similar spectrometer hardware, but different foreoptics and spectral retrieval algorithms. Accuracy, signal-to-noise, retrieval parameters, and precision were investigated for the two configurations of new miniature spectrometer. Measurements included traverses beneath the plumes from the summit and east rift zone of Kīlauea, and testing with calibration cells of known SO2 concentration. The results obtained from the different methods were consistent with each other, with <8% difference in estimated SO2 column amounts up to 800 ppm m. A further comparison between the COSPEC and one of the miniature spectrometer configurations, the ‘FLYSPEC’, spans an eight month period and showed agreement of measured emission rates to within 10% for SO2 column amounts up to 1,600 ppm m. The topic of measuring high SO2 burdens accurately is addressed for the Kīlauea measurements. In comparing the foreoptics, retrieval methods, and resultant implications for data quality, we aim to consolidate the various experiences to date, and improve the application and development of miniature spectrometer systems.

Abstract Much of the volcanological work carried out in north Afar (Ethiopia and Eritrea) has focused on the nature of Quaternary basaltic volcanic ranges, which have been interpreted by some as incipient oceanic ridges. However, we show here that comparable volumes of silicic magmas have been erupted in the region. In particular, the virtually undocumented Nabro Volcanic Range, which runs NNE for more than 100 km from the margin of the Danakil Depression to the Red Sea coast, has a subaerial volume of the order of 550 km3, comparable to the volume of the much better known Erta’Ale axial volcanic range. Nabro volcano itself forms part of an enigmatic double caldera structure with a neighbouring volcano, Mallahle. The twin caldera may have formed simultaneously with the eruption of between 20 and 100 km3 of ignimbrite, which is readily identified in Landsat Thematic Mapper imagery. This may have been the largest explosive eruption in north Afar, and is certain to have deposited a regionally distributed tephra layer which could in the future be located in distal sections as a stratigraphic marker. An integrated analysis of optical and synthetic aperture radar imagery, digital topographic data, field observations and limited geochemical measurements, permits here descriptions and first order inferences about the structure, stratigraphy and compositions of several major volcanoes of the Afar Triangle, and a reappraisal of their regional significance.

A compilation and analysis of the size and frequency of the largest known explosive eruptions on Earth are presented. The ‘largest’ explosive events are defined to be those eruptions yielding greater than 10 15 kg of products (>150 times the mass of the 1991 eruption of Mt. Pinatubo). This includes all known eruptions with a volcanic explosivity index (VEI) of 8. A total of 47 such events, ranging in age from Ordovician to Pleistocene, are identified, of which 42 eruptions are known from the past 36 Ma. A logarithmic ‘magnitude’ scale of eruption size is applied, based on erupted mass, to these events. On this scale, 46 eruptions >10 15 kg are defined to be of magnitude M8. There is one M9 event known so far, the Fish Canyon Tuff, with an erupted mass of >10 16 kg and a magnitude of 9.2. Analysis of this dataset indicates that eruptions of size M8 and larger have occurred with a minimum frequency of ≈1.4 events/Ma in two pulses over the past 36 Ma. On the basis of the activity during the past 13.5 Ma, there is at least a 75% probability of a M8 eruption (>10 15 kg) occurring within the next 1 Ma. There is a 1% chance of an eruption of this scale in the next 460–7,200 years. While the effect of any individual M8 or larger eruption is considerable, the time-averaged impact (i.e., erupted mass×frequency) of the very largest eruptions is small, due to their rarity. The long-term, time-averaged erupted mass flux from magnitude 8 and 9 eruptions is ~10–100 times less than for M7 eruptions; the time-averaged mass eruption rate from M7 eruptions is 9,500 kg s −1, whereas for M8 and M9 eruptions it is ~70–1,000 kg s −1. Comparison of the energy release by volcanic eruptions with that due to asteroid impacts suggests that on timescales of <100,000 years, explosive volcanic eruptions are considerably more frequent than impacts of similar energy yield. This has important implications for understanding the risk of extreme events.

During unusually high rainfall associated with Hurricane Mitch in 1998, a flank collapse leading to a disastrous lahar occurred at Casita volcano, Nicaragua. The lack of a similar failure during a rainfall event of comparable magnitude in 1982 (Tropical Storm Alleta) suggests that additional factors influenced the 1998 collapse. We have investigated the potential contribution of erosional flank undercutting, seismic activity and anthropogenic land-cover change at the collapse site. Except for seismic events prior to Mitch, which may have increased flank instability, none of these factors appears significant. Instead, for failure to occur, the following conditions were required: (1) highly fractured slope material allowing deep and rapid infiltration of meteoric water, (2) a less permeable underlying layer to obstruct drainage, (3) strong, continuous antecedent rainfall to build up high pore-water pressure, and (4) episodic, high-intensity precipitation during Mitch to generate recurrent pressure waves. Prerequisite (1) was provided by edifice-wide deformation towards the south-east, seismic activity and proximity to a prominent fault, and local subsidence. Condition (2) was met by clay-rich layers resulting from hydrothermal alteration. More than 1,900 mm of rain fell in the 6 months prior to Mitch without significant interruption, while intense episodic precipitation occurred during the hurricane, satisfying conditions (3) and (4), respectively. The main difference with Alleta was that it occurred at the beginning of the rainy season and, therefore, without sufficient antecedent rainfall. Anthropogenic activity, including land-cover change, did not affect slope stability (i.e. the hazard). However, vulnerability was generated when two towns were established in the lowlands south of Casita, on top of previous lahar deposits. It was greatly increased when approximately 4 km of forest between the collapse site and the towns were cleared, paving the way for a largely unobstructed debris flow. Deforestation also facilitated erosion along the flanks to provide about 78% of the material contained in the lahar when it destroyed the towns, killing more than 2,500 people.

HCl:SO2mass ratios measured by open path Fourier transform spectroscopy (OP-FTIR) in the volcanic plume at Soufrière Hills Volcano, Montserrat, are presented for the second phase of dome building between November 1999 and November 2000. HCl:SO2mass ratios of greater than 1 and HCl emission rates of greater than 400 t day–1 characterise periods of dome building for this volcano. The data suggest that chlorine partitions into a fluid phase as the magma decompresses and exsolves water during ascent. This is substantiated by a correlation between chlorine and water content in the melt (derived from the geochemical analysis of plagioclase melt inclusion and matrix glasses from phase I and II of dome growth). The matrix glass from the November 1999 and March 2000 domes indicate an open system degassing regime with a fluid-melt partition coefficient for chlorine of the order of 250–300. September 1997 glasses have higher chlorine contents and may indicate a switch to closed system degassing prior to explosive activity in September and October 1997. The OP-FTIR HCl time series suggests that HCl emission rate is strongly related to changes in eruption rate and we infer an emission rate of over 13.5 kt day–1HCl during a period of high extrusion rate in September 2000. A calculation of the HCl emission rate expected for varying extrusion rates from the open-system degassing model suggests a HCl emission rate of the order of 1–4 kt day–1is indicative of an extrusion rate of between 2 and 8 m3s–1. Monitoring of HCl at Soufrière Hills Volcano provide a proxy for extrusion rate, with changes in ratio between HCl and SO2occurring rapidly in the plume. Order of magnitude changes occur in HCl emission rates over the time-scale of hours to days, making these changes easy to detect during the day-to-day monitoring of the volcano. Mean water emission rates are calculated to range from 9–24 kt day–1during dome building activity, calculated from the predicted mass ratio of H2O:HCl in the fluid at the surface and FTIR-derived HCl emission rates.

Monitoring gases from andesite volcanoes for hazard mitigation or scientific enquiry is complicated by the wide range of eruption styles. Monitoring is aimed at both measuring the rates of gas emission, and changes in their compositions. Direct sampling techniques are restricted to accessible vents, and are unsuitable for syn-eruption monitoring. Correlation spectroscopy is a simple and robust method for measuring emission rates of sulphur dioxide, but is subject to large errors. Open-path Fourier transform spectroscopy provides a remote method for determining plume gas compositions, but requires careful atmospheric radiative transfer modelling. Few andesite volcanoes have been consistently monitored. Published data show that there is no simple general model for volcano degassing: each volcano, and each eruption, presents separate problems, many of them arising from the evolving interaction between magmatic and hydrothermal systems during an episode of activity. Because of its lower solubility in magmas and conservative behaviour in hydrothermal systems, remote measurements of carbon dioxide proportions and emission rates would be extremely valuable for monitoring, but they remain difficult because of its high atmospheric concentration.

Volcanic gases have important climatic and environmental effects, and provide insights into magmatic processes. Direct sampling of volcanic gases is inherently difficult and often hazardous. Here, we report the results of long path measurements of SO2and HCl from Mt. Etna and Vulcano (Italy) obtained by active mode Fourier Transform InfraRed (FTIR) spectroscopy. Spectra recorded in September 1994 over path lengths of up to 2 km indicate SO2∶HCl ratios of 3–5∶1 for Etna, and 0.7–1.4∶1 for Vulcano, consistent with their different styles of activity. Combined with contemporaneous Correlation Spectrometer (COSPEC) SO2flux measurements, these ratios indicate an HCl flux for Etna of about 1700 t/d (about 16% of the present global anthropogenic flux) and for Vulcano of about 13 t/d. We also report the first remote spectroscopic detection of volcanic SiF4.

The behaviour of magmatic volatiles dictates various aspects of a subaerial volcano's eruptive style, morphology, and potential impact on the atmosphere. Typically, when volatiles bleed from nonerupting magma bodies, they encounter superimposed hydrothermal envelopes. If their interaction with hydrothermal fluids is minimal, subaerial degassing may be important, and possibly manifested in high fluxes of gaseous SO2. By contrast, a “wet” volcano, in which there is substantial mixing of magmatic and hydrothermal fluids, scavenges reactive magmatic components: sulfur‐bearing minerals precipitate in crater lakes, in pore spaces created by hydrothermal dissolution of host rock, and in fractures formed by caldera collapse. Measurements of subaerial SO2fluxes (e.g., by Correlation Spectrometer, COSPEC) therefore say as much about hydrothermal vigour as they do about magma bodies. Major explosive eruptions necessarily entail reaming of conduits through volcanic edifices, and entrainment of hydrothermal sulfur. It is argued here that eruption clouds might thereby derive significant proportions of their SO2budget from combustion of native sulfur and/or sulfides sequestered by hydrothermal systems during inter‐eruptive periods of >10²–10³ yr.

The author discusses the on the gap between science and policy which came in to the sight due to the volcanic ash crises of 2010-11 in Iceland. He informs that there have been improvements in measuring airborne ash concentrations, increased harmonisation of civil aviation control across and the introduction of higher thresholds for jet engine tolerance for ash in Europe.

We report results from a inultidisciplinary campaign conducted at Poás volcano (Costa Rica) in March 2009. Thermal imagery of the fumaroles sited on the north side of the pyroclastic cone revealed mean apparent temperatures ranging between 25 and 40°C with a maximum apparent temperature of 80cC. The crater lake surface was characterised by mean apparent temperatures varying between 30 and 35°C and a maximum recorded value of 48°C. Thermal profiles across the lake surface revealed steady temperatures and thus thorough convective mixing. The overall mean SO2 flux emitted from the crater was 76 Mg d-1, with approximately equal contributions from both the pyroclastic cone and the lake. Analysis of gas composition using active, open-path FTIR spectroscopy indicated molar ratios of H2O/SO2 =151, CO2/SO2 = 1.56, SO2/HC1 > 40, and SO2/HF > 200 for the lake emission. The plume was also sampled using filter packs. Ion chromatographic analysis revealed the presence of abundant K+ and SO4², with small amounts of Ca2+, Cl, and Mg2+. This provides a detailed picture of lake surface temperature characteristics and of gas flux and composition of the plume emitted from Poás. The results are consistent with the typical non-eruptive state of this volcano. [ABSTRACT FROM AUTHOR]