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CO2 emissions during the 2023 Litli Hrútur eruption in Reykjanes, Iceland: ẟ13C tracks magma degassing
Abstract
We report CO2 emission rates and plume δ13C during the July 2023 eruption at Litli Hrútur in the Fagradalsfjall region of the Reykjanes Peninsula. The CO2 emission rates were measured by UAV utilizing a new method of data extrapolation that enables obtaining rapid flux results of dynamic eruption plumes. The δ13C values are consistent with degassing-induced isotopic fractionation of the magma during and after the eruption. Our results show that rapid, real-time CO2 flux measurements coupled with isotopic values of samples collected at the same time provide key insights into the dynamics of volcanic eruptions and have the potential of forecasting the termination of activity.
... Most of these measurements have been performed on low temperature systems (e.g., Capasso et al., 2005;Chiodini et al., 2011;Hilton et al., 2010;Obase et al., 2022;Sato et al., 2002) as isotopic measurements in gases collected at magmatic temperatures are rare and challenging (e.g., Allard, 1979;Allard et al., 1977;Gerlach & Taylor, 1990). Recent advances in in situ isotope ratio infrared spectroscopy have since allowed δ 13 C measurements in volcanic plumes emitted from the main vent of active volcanoes (e.g., D'Arcy et al., 2022;Fischer et al., 2024;Galle et al., 2021;Liu et al., 2020;Malowany et al., 2017;Rizzo et al., 2014Rizzo et al., , 2015Schipper et al., 2017). The second category of studies has focused on erupted lavas, mainly from submarine settings, with δ 13 C measurements performed on CO 2 dissolved in the glass and/or trapped in vesicles (e.g., Aubaud et al., 2004Aubaud et al., , 2005Aubaud et al., , 2006Cartigny et al., 2001;Des Marais & Moore, 1984;Jendrzejewski, 1994;Marty & Jambon, 1987;Moore et al., 1977;Pineau et al., 1976;Pineau & Javoy, 1983;Pineau & Javoy, 1994). ...
... The δ 13 C value of volcanic gases emitted during the July 2023 eruption at Litli Hrútur, 4.5 km away from the 2021 eruption, was measured by Fischer et al. (2024). Although some samples were contaminated by moss fire, they found δ 13 C values that extrapolate to between 9 and 5‰ representative of the magmatic CO 2 emitted during the eruption. ...
... Some amount of kinetic isotopic fractionation is necessary to explain the δ 13 C gas that we measured in the 2021 eruption. However, if the δ 13 C melt of our deepest melt inclusions ( 10 to 6‰) is taken as representative of magmas across the Reykjanes Peninsula at the same depth level, then δ 13 C gas values between 9 and 5‰ as reported for the 2023 Litli Hrútur eruption (Fischer et al., 2024) could be reproduced by closed system degassing (equilibrium or kinetic; Figures 6a and 6c). The δ 13 C value of hydrothermal gases in the Reykjanes Peninsula compiled by Stefánsson et al. (2017, original data therein) ranges between 5 and 3‰. ...
CO2 is the first volatile to exsolve in magmatic systems and plays a crucial role in driving magma ascent and volcanic eruptions. Carbon stable isotopes serve as valuable tracers for understanding the transfer of CO2 from the melt to the gas phase during passive degassing or active eruptions. In this study, we present δ¹³C measurements from the 2021 Fagradalsfjall eruption, obtained from (a) volcanic gases emitted during the eruption and collected via unmanned aerial systems (UAS), and (b) a series of mineral‐hosted melt inclusions from the corresponding tephra deposits. These data sets jointly track the carbon isotopic evolution of the melt and gas phases during the last 10 km of magma ascent. The isotopic evolution of both phases indicates that kinetic degassing, a process previously only identified in mid‐ocean ridge basalts, took place in the 10 to 1 km depth range, followed by equilibrium degassing at near‐surface conditions in the last kilometer. Postulating that the melt was first saturated with CO2 at 27 km depth and that degassing from then to 10 km depth took place via equilibrium isotopic fractionation, the melt inclusion data constrain the initial δ¹³C signature of the Icelandic mantle to −6.5 ± 2.5‰ but also show indications of possible isotopic heterogeneity in the mantle source.
... In fact, magmatic outgassing progressively fractionates C isotopes towards lighter δ 13 C in both the exsolved gas phase and residual melt (Halloway and Blank, 1994). This process has recently been observed during the Litli Hrútur eruption in Reykjanes (Iceland) in 2023, where the gas plume showed more positive δ 13 C CO2 values during the eruptive phase, and shifted towards more negative values after the eruption (Fischer et al., 2024). The more positive δ 13 C recorded by calcites may imply CO 2 degassing from primitive magmas during eruptive periods, whereas the lower δ 13 C CO2 of the fluids currently discharged at Krafla may reflect a degassed magma (a posteruptive period). ...
Equilibrium in the H 2 O-H 2-CO 2-CO-CH 4 gas system has been extensively applied to fumarole data for geothermal exploration and volcano monitoring. However, little is known about its application to two-phase (vapor and liquid) geothermal well fluids, which can show an excess of enthalpy. Here, we applied the H 2 O-H 2-CO 2-CO-CH 4 gas indicators to two-phase geothermal well discharges from the Krafla geothermal system, Iceland, to estimate aquifer temperatures and identify secondary processes during resource exploitation. Results suggest that the Krafla resource is drawn from a deep (approximately between-500 and-1,600 m a.s.l.), two-phase aquifer with temperatures ranging from 272 to 320 • C and vapor fractions between 0.26 and 0.93, explaining the excess enthalpy observed in well fluids. These estimates align with the temperatures of the main production zones of geothermal wells, whereas solute geothermometers (SiO 2 and Na/K) appear to record lower temperatures of minor, shallower, liquid aquifers. Wells with liquid-like enthalpy are sourced from the two-phase aquifer but are also influenced by water reinjection or downflows from a colder, shallower aquifer, consistent with the isothermal zone extending approximately between 400 and-900 m a.s.l. in Leirbotnar and Vesturhlíðar sub-fields. Water isotopes indicate the main aquifer is recharged by meteoric and reinjection fluids. Excess-enthalpy discharges show an influx of Ar-and N 2-rich vapor, with depleted 40 Ar/ 36 Ar and δ 15 N values, suggesting frac-tionations of atmospheric gases dissolved into the reservoir liquid. On the other hand, δ 13 C CO2 and 3 He/ 4 He values point to a mantle origin, despite the lower δ 13 C CO2 and P CO2 levels that reflect a degassed magma (i.e., a noneruptive phase). These findings underscore the usefulness of the H 2 O-H 2-CO 2-CO-CH 4 gas system and isotopic methods in tracking geothermal reservoir temperatures, their sources, and secondary processes, such as water reinjection or downflows from shallower aquifers.
We report in-plume carbon dioxide (CO2) concentrations and carbon isotope ratios during the 2021 eruption of Tajogaite volcano, island of La Palma, Spain. CO2 measurements inform our understanding of volcanic contributions to the global climate carbon cycle and the role of CO2 in eruptions. Traditional ground-based methods of CO2 collection are difficult and dangerous, and as a result only about 5 % of volcanoes have been directly surveyed. We demonstrate that unpiloted aerial system (UAS) surveys allow for fast and relatively safe measurements. Using CO2 concentration profiles we estimate the total flux during several measurements in November 2021 to be 1.76±0.20×103 to 2.23±0.26×104 t d-1. Carbon isotope ratios of plume CO2 indicate a deep magmatic source, consistent with the intensity of the eruption. Our work demonstrates the feasibility of UASs for CO2 surveys during active volcanic eruptions, particularly for deriving rapid emission estimates.
We report in-plume carbon dioxide (CO2) concentrations and isotope ratios during an active eruption of the Tajogaite Volcano. CO2 measurements inform our understanding of volcanic contributions to the global climate carbon cycle, and the role of CO2 in eruptions. Traditional ground-based methods of CO2 collection are difficult and dangerous, as a result only 5 % of volcanoes have been surveyed. We demonstrate that Unpiloted Aerial System (UAS) surveys allow for fast and relatively safe measurements. Using CO2 concentration profiles we estimate total flux to be 1.19 × 106 to 2.80 × 107 t day−1. Isotope ratios indicated a deep magmatic source, consistent with the intensity of the eruption. Our work demonstrates the feasibility of UASs for CO2 surveys during active volcanic eruptions, particularly in calculating plume characteristics.
Alkaline mafic magmas forming intra-plate oceanic islands are believed to be strongly enriched in CO2 due to low-degree partial melting of enriched mantle sources. However, until now, such CO2 enhancement has not been verified by measuring CO2 degassing during a subaerial eruption. Here, we provide evidence of highly CO2-rich gas emissions during the 86-day 2021 Tajogaite eruption of Cumbre Vieja volcano on La Palma Island, in the Canary archipelago. Our results reveal sustained high plume CO2/SO2 ratios, which, when combined with SO2 fluxes, melt inclusion volatile contents and magma production rates at explosive and effusive vents, imply a magmatic CO2 content of 4.5 ± 1.5 wt%. The amount of CO2 released during the 2021 eruptive activity was 28 ± 14 Mt CO2. Extrapolating to the volume of alkaline mafic magmas forming La Palma alone (estimated as 4000 km³ erupted over 11 Ma), we infer a maximum CO2 emission into the ocean and atmosphere of 10¹⁶ moles of CO2, equivalent to 20% of the eruptive CO2 emissions from a large igneous province eruption, suggesting that the formation of the Canary volcanic archipelago produced a CO2 emission of similar magnitude as a large igneous province.
Lava fountains are a common manifestation of basaltic volcanism. While magma degassing plays a clear key role in their generation, the controls on their duration and intermittency are only partially understood, not least due to the challenges of measuring the most abundant gases, H2O and CO2. The 2021 Fagradalsfjall eruption in Iceland included a six-week episode of uncommonly periodic lava fountaining, featuring ~ 100–400 m high fountains lasting a few minutes followed by repose intervals of comparable duration. Exceptional conditions on 5 May 2021 permitted close-range (~300 m), highly time-resolved (every ~ 2 s) spectroscopic measurement of emitted gases during 16 fountain-repose cycles. The observed proportions of major and minor gas molecular species (including H2O, CO2, SO2, HCl, HF and CO) reveal a stage of CO2 degassing in the upper crust during magma ascent, followed by further gas-liquid separation at very shallow depths (~100 m). We explain the pulsatory lava fountaining as the result of pressure cycles within a shallow magma-filled cavity. The degassing at Fagradalsfjall and our explanatory model throw light on the wide spectrum of terrestrial lava fountaining and the subsurface cavities associated with basaltic vents.
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 magmas4,5 is 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 107–108 m3 of 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. Primitive lavas of the Fagradalsfjall eruption present a window into the deep roots of a magmatic system previously inaccessible to near-real-time investigation, showing that eruptible batches of basaltic magma mix on a timescale of weeks.
The basaltic effusive eruption at Mt. Fagradalsfjall lasted from 19 March to 18 September 2021, ending a 781‐year repose period on Reykjanes Peninsula, Iceland. By late September 2021, 33 near real‐time photogrammetric surveys were completed using satellite and airborne images, usually processed within 3–6 hr. The results provide unprecedented temporal data sets of lava volume, thickness, and effusion rate. This enabled rapid assessment of eruption evolution and hazards to populated areas, important infrastructure, and tourist centers. The lava flow field has a mean lava thickness exceeding 30 m, covers 4.8 km² and has a bulk volume of 150 ± 3 × 10⁶ m³. The March–September mean bulk effusion rate is 9.5 ± 0.2 m³/s, ranging between 1 and 8 m³/s in March–April and increasing to 9–13 m³/s in May–September. This is uncommon for recent Icelandic eruptions, where the highest discharge usually occurs in the opening phase.
We present methods for autonomous collaborative surveying of volcanic CO2 emissions using aerial robots. CO2 is a useful predictor of volcanic eruptions and an influential greenhouse gas. However, current CO2 mapping methods are hazardous and inefficient, as a result, only a small fraction of CO2 emitting volcanoes have been surveyed. We develop algorithms and a platform to measure volcanic CO2 emissions. The Dragonfly Unpiloted Aerial Vehicle (UAV) platform is capable of long-duration CO2 collection flights in harsh environments. We implement two survey algorithms on teams of Dragonfly robots and demonstrate that they effectively map gas emissions and locate the highest gas concentrations. Our experiments culminate in a successful field test of collaborative rasterization and gradient descent algorithms in a challenging real-world environment at the edge of the Valles Caldera supervolcano. Both algorithms treat multiple flocking UAVs as a distributed flexible instrument. Simultaneous sensing in multiple UAVs gives scientists greater confidence in estimates of gas concentrations and the locations of sources of those emissions. These methods are also applicable to a range of other airborne concentration mapping tasks, such as pipeline leak detection and contaminant localization.
A multi-rotor drone has been adapted for studies of volcanic gas plumes. This adaptation includes improved capacity for high-altitude and long-range, real-time SO2 concentration monitoring, long-range manual control, remotely activated bag sampling and plume speed measurement capability. The drone is capable of acting as a stable platform for various instrument configurations, including multi-component gas analysis system (MultiGAS) instruments for in situ measurements of SO2, H2S, and CO2 concentrations in the gas plume and portable differential optical absorption spectrometer (MobileDOAS) instruments for spectroscopic measurement of total SO2 emission rate, remotely controlled gas sampling in bags and sampling with gas denuders for posterior analysis on the ground of isotopic composition and halogens.
The platform we present was field-tested during three campaigns in Papua New Guinea: in 2016 at Tavurvur, Bagana and Ulawun volcanoes, in 2018 at Tavurvur and Langila volcanoes and in 2019 at Tavurvur and Manam volcanoes, as well as in Mt. Etna in Italy in 2017.
This paper describes the drone platform and the multiple payloads, the various measurement strategies and an algorithm to correct for different response times of MultiGAS sensors. Specifically, we emphasize the need for an adaptive flight path, together with live data transmission of a plume tracer (such as SO2 concentration) to the ground station, to ensure optimal plume interception when operating beyond the visual line of sight. We present results from a comprehensive plume characterization obtained during a field deployment at Manam volcano in May 2019. The Papua New Guinea region, and particularly Manam volcano, has not been extensively studied for volcanic gases due to its remote location, inaccessible summit region and high level of volcanic activity. We demonstrate that the combination of a multi-rotor drone with modular payloads is a versatile solution to obtain the flux and composition of volcanic plumes, even for the case of a highly active volcano with a high-altitude plume such as Manam. Drone-based measurements offer a valuable solution to volcano research and monitoring applications and provide an alternative and complementary method to ground-based and direct sampling of volcanic gases.
A multi-copter drone has been adapted for studies of volcanic gas plumes. This adaptation includes improved capacity for high altitude and long range, real-time SO2 concentration monitoring, long range manual control, remotely-activated bag sampling, and plume speed measurement capability. The drone is capable of acting as a stable platform for various instrument configurations including: MultiGAS instruments for in-situ measurements of SO2, H2S, CO2 and H2O concentrations in the gas plume, MobileDOAS instruments for spectroscopic measurement of total SO2 emission rate, remotely-controlled gas sampling in bags and sampling with gas denuders for posterior analysis on the ground of isotopic composition and halogens. The platform we present has been field-tested during three campaigns in Papua New Guinea: in 2016 at Tavurvur, Bagana and Ulawun volcanoes, in 2018 at Tavurvur and Langila volcanoes and in 2019 at Tavurvur and Manam volcanoes; as well as in Mt. Etna in Italy in 2017. This paper describes the drone platform and the multiple payloads, the various measurement strategies, an algorithm to correct for different time-responses of MultiGAS sensors. Specifically, we emphasise the need for an adaptive flight path, together with live data transmission of a plume tracer (such as SO2 concentration) to the ground station, to ensure optimal plume interception when operating beyond visual line of sight. We present results from a comprehensive plume characterization obtained during a field deployment at Manam volcano in May 2019. The Papua New Guinea region, and particularly Manam volcano, has not been extensively studied for volcanic gases due to its remote location, inaccessible summit region and high level of volcanic activity. We demonstrate that the combination of a multi-rotor with modular payloads is a versatile solution to obtain the flux and composition of volcanic plumes, even for the case of a highly active volcano with a high-altitude plume such as Manam. Drone-based measurements offer a valuable solution to volcano research and monitoring applications, and provide an alternative and complementary method to ground-based and direct sampling of volcanic gases.
Plain Language Summary
Carbon dioxide (CO2) is a greenhouse gas that plays a predominant role in climate change. Volcanoes emit CO2 and play a role in the global carbon cycle; however, the amount of CO2 they emit is highly uncertain. One of the main reasons for this uncertainty is the limited amount of volcanic emission measurements available to estimate these CO2 emissions. Satellites retrieving CO2 have an advantage over ground‐based measurements as they have the potential to obtain data over the entire globe. After the launch of National Aeronautics and Space Administration (NASA)'s Orbiting Carbon Observatory‐2 (OCO‐2) satellite in 2014, spaceborne observations of volcanic CO2 were possible. This study uses OCO‐2 measurements of CO2 to estimate emissions during the 2018 Kilauea volcano eruption and is the first to trace satellite CO2 data downwind from the source of a major volcanic eruption. Here we show that the Kilauea volcano eruption emitted large amounts of CO2 and OCO‐2 proved capable to observe the large atmospheric concentrations associated with these emissions.
Volcanic emissions are a critical pathway in Earth's carbon cycle. Here, we show that aerial measurements of volcanic gases using unoccupied aerial systems (UAS) transform our ability to measure and monitor plumes remotely and to constrain global volatile fluxes from volcanoes. Combining multi-scale measurements from ground-based remote sensing, long-range aerial sampling, and satellites, we present comprehensive gas fluxes - 3760 ± [600, 310] tons day−1 CO2 and 5150 ± [730, 340] tons day−1 SO2 - for a strong yet previously uncharac-terized volcanic emitter: Manam, Papua New Guinea. The CO2/T ratio of 1.07 ± 0.06 suggests a modest slab sediment contribution to the sub-arc mantle. We find that aerial strategies reduce uncertainties associated with ground-based remote sensing of SO2 flux and enable near-real-time measurements of plume chemistry and carbon isotope composition. Our data emphasize the need to account for time averaging of temporal variability in volcanic gas emissions in global flux estimates.
Quantifying the global volcanic CO2 output from subaerial volcanism is key for a better understanding of rates and mechanisms of carbon cycling in and out of our planet and their consequences for the long‐term evolution of Earth's climate over geological timescales. Although having been the focus of intense research since the early 1990s, and in spite of recent progress, the global volcanic CO2 output remains inaccurately known. Here we review past developments and recent progress and examine limits and caveats of our current understanding and challenges for future research. We show that CO2 flux measurements are today only available for ~100 volcanoes (cumulative measured flux, 44 Tg CO2/year), implying that extrapolation is required to account for the emissions of the several hundred degassing volcanoes worldwide. Recent extrapolation attempts converge to indicate that persistent degassing through active crater fumaroles and plumes releases ~53–88 Tg CO2/year, about half of which is released from the 125 most actively degassing subaerial volcanoes (36.4 ± 2.4 Tg CO2/year from strong volcanic gas emitters, Svge). The global CO2 output sustained by diffuse degassing via soils, volcanic lakes, and volcanic aquifers is even less well characterized but could be as high as 83 to 93 Tg CO2/year, rivaling that from the far more manifest crater emissions. Extrapolating these current fluxes to the past geological history of the planet is challenging and will require a new generation of models linking subduction parameters to magma and volatile (CO2) fluxes.
Volcanism and metamorphism are the principal geologic processes that drive carbon transfer from the interior of Earth to the surface reservoir. 1-4 Input of carbon to the surface reservoir through volcanic degassing is balanced by removal through silicate weathering and the subduction of carbon-bearing marine deposits over million-year timescales. The magnitude of the volcanic carbon flux is thus of fundamental importance for stabilization of atmospheric CO 2 and for long-term climate. It is likely that the "deep" carbon reservoir far exceeds the size of the surface reservoir in terms of mass; 5,6 more than 99% of Earth's carbon may reside in the core, mantle, and crust. The relatively high flux of volcanic carbon to the surface reservoir, combined with the reservoir's small size, results in a short residence time for carbon in the ocean-atmosphere-biosphere system (~200 ka). 7 The implication is that changes in the flux of volcanic carbon can affect the climate and ultimately the habitability of the planet on geologic timescales. In order to understand this delicate balance, we must first quantify the current volcanic flux of carbon to the atmosphere and understand the factors that control this flux. The three most abundant magmatic volatiles are water (H 2 O), carbon dioxide (CO 2), and sulfur (S), with CO 2 being the least soluble in silicate melts. 8 For this reason, it is not only Earth's active volcanoes that are a source of magmatic CO 2 , but also numerous inactive volcanoes with magma bodies present at depth in the crust that contribute to the carbon emissions (Figure 8.1). Emissions from active volcanoes are released through crater fumaroles and open vents to form visible volcanic plumes, but diffuse degassing and degassing through springs o
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Persistent non-explosive passive degassing is a common characteristic of active volcanoes. Distinct periodic components in measurable parameters of gas release have been widely identified over timescales ranging from seconds to months. The development and implementation of high temporal resolution gas measurement techniques now enables the robust quantification of high frequency processes operating on timescales comparable to those detectable in geophysical datasets. This review presents an overview of the current state of understanding regarding periodic volcanic degassing, and evaluates the methods available for detecting periodicity, e.g., autocorrelation, variations of the Fast Fourier Transform (FFT), and the continuous wavelet transform (CWT). Periodicities in volcanic degassing from published studies were summarised and statistically analysed together with analyses of literature-derived datasets where periodicity had not previously been investigated. Finally, an overview of current knowledge on drivers of periodicity was presented and discussed in the framework of four main generating categories, including: (1) non-volcanic (e.g., atmospheric or tidally generated); (2) gas-driven, shallow conduit processes; (3) magma movement, intermediate to shallow storage zone; and (4) deep magmatic processes.
We use both seismology and geobarometry to investigate the movement of melt through the volcanic crust of Iceland. We have captured melt in the act of moving within or through a series of sills ranging from the upper mantle to the shallow crust by the clusters of small earthquakes it produces as it forces its way upward. The melt is injected not just beneath the central volcanoes, but also at discrete locations along the rift zones and above the centre of the underlying mantle plume. We suggest that the high strain rates required to produce seismicity at depths of 10–25 km in a normally ductile part of the Icelandic crust are linked to the exsolution of carbon dioxide from the basaltic melts. The seismicity and geobarometry provide complementary information on the way that the melt moves through the crust, stalling and fractionating, and often freezing in one or more melt lenses on its way upwards: the seismicity shows what is happening instantaneously today, while the geobarometry gives constraints averaged over longer time scales on the depths of residence in the crust of melts prior to their eruption.
This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics'.
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.
Volcanic degassing is one of the main natural sources of CO2 to the atmosphere. Carbon isotopes
of volcanic gases enable the determination of CO2 sources including mantle, organic or carbonate sediments,
and atmosphere. Until recently, this work required sample collection from vents followed by laboratory
analyses. Isotope ratio infrared analyzers now enable rapid analyses of plume δ13C-CO2, in situ and in real time.
Here we report the first analyses of δ13C-CO2 from airborne samples. These data combined with plume samples
from the vent area enable extrapolation to the volcanic source δ13C. We performed our experiment at
the previously unsampled and remote Kanaga Volcano in the Western Aleutians. We find a δ13C source
composition of �4.4‰, suggesting that CO2 from Kanaga is primarily sourced from the upper mantle with
minimal contributions from subducted components. Our method is widely applicable to volcanoes where
remote location or activity level precludes sampling using traditional methods.
The 2009 eruption of Redoubt Volcano, Alaska was particularly well monitored for volcanic gas emissions. We report 35 airborne measurements of CO2, SO2, and H2S emission rates that span from October 2008 to August 2010. The magmatic system degassed primarily as a closed system although minor amounts of open system degassing were observed in the 6 months prior to eruption on March 15, 2009 and over 1 year following cessation of dome extrusion. Only 14% of the total CO2 was emitted prior to eruption even though high emissions rates (between 3630 and 9020 t/d) were observed in the final 6 weeks preceding the eruption. A minor amount of the total SO2 was observed prior to eruption (4%), which was consistent with the low emission rates at that time (up to 180 t/d). The amount of the gas emitted during the explosive and dome growth period (March 15-July 1, 2009) was 59 and 66% of the total CO2 and SO2, respectively. Maximum emission rates were 33,110 t/d CO2, 16,650 t/d SO2, and 1230 t/d H2S. Post-eruptive passive degassing was responsible for 27 and 30% of the total CO2 and SO2, respectively. SO2 made up on average 92% of the total sulfur degassing throughout the eruption. Magmas were vapor saturated with a C- and S-rich volatile phase, and regardless of composition, the magmas appear to be buffered by a volatile composition with a molar CO2/SO2 ratio of ~ 2.4. Primary volatile contents calculated from degassing and erupted magma volumes range from 0.9 to 2.1 wt.% CO2 and 0.27-0.56 wt.% S; whole-rock normalized values are slightly lower (0.8-1.7 wt.% CO2 and 0.22-0.47 wt.% S) and are similar to what was calculated for the 1989-90 eruption of Redoubt. Such contents argue that primary arc magmas are rich in CO2 and S. Similar trends between volumes of estimated degassed magma and observed erupted magma during the eruptive period point to primary volatile contents of 1.25 wt.% CO2 and 0.35 wt.% S. Assuming these values, up to 30% additional unerupted magma degassed in the year following final dome emplacement.
The low-intensity activity of basaltic volcanoes is occasionally
interrupted by short-lived but energetic explosions which, whilst
frequently observed, are amongst the most enigmatic volcanic events in
Nature. The combination of poorly understood and deep, challenging to
measure, source processes make such events currently impossible to
forecast. Here we report increases in quiescent degassing CO2
emissions (>10,000 t/day) prior to a powerful explosive event on
Stromboli volcano on 15 March 2007. We interpret such large
CO2 flux as being sourced by passive gas leakage from a
deeply (>4 km) stored magma, whose depressurization, possibly caused
by the onset of an effusive eruption on 28 February 2007, was the
explosion trigger. Our observations suggest that continuous
CO2 flux monitoring may allow anomalously large explosions to
be accurately forecast at basaltic volcanoes.
Over long periods of time (~Ma), we may consider the oceans, atmosphere and biosphere
as a single exospheric reservoir for CO2. The geological carbon cycle describes the inputs to
this exosphere from mantle degassing, metamorphism of subducted carbonates and outputs
from weathering of aluminosilicate rocks (Walker et al. 1981). A feedback mechanism relates
the weathering rate with the amount of CO2 in the atmosphere via the greenhouse effect (e.g.,
Wang et al. 1976). An increase in atmospheric CO2 concentrations induces higher temperatures,
leading to higher rates of weathering, which draw down atmospheric CO2 concentrations (Berner
1991). Atmospheric CO2 concentrations are therefore stabilized over long timescales by this
feedback mechanism (Zeebe and Caldeira 2008). This process may have played a role (Feulner
et al. 2012) in stabilizing temperatures on Earth while solar radiation steadily increased due to
stellar evolution (Bahcall et al. 2001). In this context the role of CO2 degassing from the Earth is
clearly fundamental to the stability of the climate, and therefore to life on Earth. Notwithstanding
this importance, the flux of CO2 from the Earth is poorly constrained. The uncertainty in our
knowledge of this critical input into the geological carbon cycle led Berner and Lagasa (1989)
to state that it is the most vexing problem facing us in understanding that cycle.
The crustal Urey cycle of CO2 involving silicate weathering and metamorphism acts as a dynamic climate buffer. In this cycle, warmer temperatures speed silicate weathering and carbonate formation, reducing atmospheric CO2 and thereby inducing global cooling. Over long periods of time, cycling of CO2 into and out of the mantle also dynamically buffers CO2. In the mantle cycle, CO2 is outgassed at ridge axes and island arcs, while subduction of carbonatized oceanic basalt and pelagic sediments returns CO2 to the mantle. Negative feedback is provided because the amount of basalt carbonatization depends on CO2 in seawater and therefore on CO2 in the air. On the early Earth, processes involving tectonics were more vigorous than at present, and the dynamic mantle buffer dominated over the crustal one. The mantle cycle would have maintained atmospheric and oceanic CO2 reservoirs at levels where the climate was cold in the Archean unless another greenhouse gas was important. Reaction of CO2 with impact ejecta and its eventual subduction produce even lower levels of atmospheric CO2 and small crustal carbonate reservoirs in the Hadean. Despite its name, the Hadean climate would have been freezing unless tempered by other greenhouse gases.
Volcanic CO2 emission rate data are sparse despite their potential importance for constraining the role of magma degassing in the biogeochemical cycle of carbon and for assessing volcanic hazards. We used a LI-COR CO2 analyzer to determine volcanic CO2 emission rates by airborne measurements in volcanic plumes at Popocatépetl volcano on June 7 and 10, 1995. LI-COR sample paths of ~72m, compared with ~1km for the analyzer customarily used, together with fast Fourier transforms to remove instrument noise from raw data greatly improve resolution of volcanic CO2 anomalies. Parametric models fit to background CO2 provide a statistical tool for distinguishing volcanic from ambient CO2. Global Positioning System referenced flight traverses provide vastly improved data on the shape, coherence, and spatial distribution of volcanic CO2 in plume cross sections and contrast markedly with previous results based on traverse stacking. The continuous escape of CO2 and SO2 from Popocatépetl was fundamentally noneruptive and represented quiescent magma degassing from the top of a magma chamber ~5km deep. The average CO2 emission rate for January-June 1995 is estimated to be at least 6400td-1, one of the highest determined for a quiescently degassing volcano, although correction for downwind dispersion effects on volcanic CO2 indicates a higher rate of ~9000td-1. Analysis of random errors indicates emission rates have 95% confidence intervals of ~+/-20%, with uncertainty contributed mostly by wind speed variance, although the variance of plume cross-sectional areas during traversing is poorly constrained and possibly significant.
We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic
composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct
sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are
in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at
volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method
to Mount Etna where we derived a δ13C of volcanic CO2 between −0.9 ± 0.27‰ and −1.41 ± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported
in previous work highlights a temporal trend of systematic increase of δ13C values of Etna CO2 from ~ −4‰, in the 1970’s and the 1980’s, to ~ −1‰ at the present time (2009). This shift toward more positive δ13C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss
such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to
magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the
carbon isotopic composition of the CO2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.
KeywordsVolcanic plume–Carbon isotope–Etna–Magmatic degassing
Strombolian-type eruptive activity, common at many volcanoes, consists of regular explosions driven by the bursting of gas
slugs that rise faster than surrounding magma. Explosion quakes associated with this activity are usually localized at shallow
depth; however, where and how slugs actually form remain poorly constrained. We used spectroscopic measurements performed
during both quiescent degassing and explosions on Stromboli volcano (Italy) to demonstrate that gas slugs originate from as
deep as the volcano-crust interface (∼3 kilometers), where both structural discontinuities and differential bubble-rise speed
can promote slug coalescence. The observed decoupling between deep slug genesis and shallow (∼250-meter) explosion quakes
may be a common feature of strombolian activity, determined by the geometry of plumbing systems.
Carbon dioxide emissions from volcanoes are important parameters to constrain in order to fully understand the Earth system, especially the effect of volcanic forcing on climate. The characterization of carbon concentration in magmas has been used to constrain volcanic fluxes. Because of low CO2 solubility in silicate melts, however, CO2 is significantly degassed from magmas due to decompression during transfer to the surface. The measurement of the carbon stable isotope ratio (¹³C/¹²C expressed as δ¹³C-values) in natural submarine glasses has been a helpful geochemical tool to study magma degassing. Carbon stable isotope fractionation at magmatic temperature between CO2 in vesicles and carbonate ions dissolved in the melt is still large enough to cause variations in δ¹³C-values. This variability can be used to deduce the mode of degassing (open vs. closed system, equilibrium vs. kinetic) operating in a given magmatic system.
In this study, I present a review of the existing carbon isotope data for magmas of three different settings (ridge, hotspot and arc). This review allows to (1) investigate the diversity of degassing modes operating within a given setting and (2) compare the prevailing degassing mode between these three settings.
Except for rare undersaturated samples and for volatile-rich, vesicular popping rocks, Mid-Ocean Ridge Basalts (MORBs) are predominantly extensively degassed and supersaturated in CO2 reflecting incomplete degassing during their last degassing step. Such a behavior is also reflected in their vesicle-dissolved carbon isotopic fractionations that are generally smaller than equilibrium values stemming from kinetic/diffusive effects. By contrast, the CO2 + H2O gas phase in hotspot and arc magmas is predominantly in chemical equilibrium with the melt because of volatile-rich initial conditions (and thus larger vesicularity) enhancing vapor-melt chemical and isotopic equilibrium. This larger initial volatile content is responsible for the extensive open-system (Rayleigh distillation) degassing generally observed in hotspot and arc magmas.
This review highlights the fact that one single degassing model cannot explain the geochemical evolution of all magmas. Also, no single model can be assigned to one specific type of magma (i.e., a significant diversity of degassing mode exists within a given type of magma, notably in MORBs). It is important to take into account these observations when degassing corrections are applied on the basis of noble gas (He/Ne or He/Ar) ratios. It appears helpful to characterize the carbon concentration and stable isotope ratios in vesicles and dissolved in the glass in order to (1) identify the mode of degassing operating in a given magmatic system and (2) apply the most appropriate degassing correction to these magmas. It is only after this critical correcting step has been achieved that an assessment of initial magmatic CO2 contents can be reasonably undertaken.
The term "carbon cycle" is normally thought to mean those processes that govern the present-day transfer of carbon between life, the atmosphere, and the oceans. This book describes another carbon cycle, one which operates over millions of years and involves the transfer of carbon between rocks and the combination of life, the atmosphere, and the oceans. The weathering of silicate and carbonate rocks and ancient sedimentary organic matter (including recent, large-scale human-induced burning of fossil fuels), the burial of organic matter and carbonate minerals in sediments, and volcanic degassing of carbon dioxide contribute to this cycle. In The Phanerozoic Carbon Cycle, Robert Berner shows how carbon cycle models can be used to calculate levels of atmospheric CO2 and O2 over Phanerozoic time, the past 550 million years, and how results compare with independent methods. His analysis has implications for such disparate subjects as the evolution of land plants, the presence of giant ancient insects, the role of tectonics in paleoclimate, and the current debate over global warming and greenhouse gases
INTRODUCTION
Although the carbon budget is often presented in terms of global-scale fluxes, many of the contributing processes occur through localized point sources, which have been challenging to measure from space. Persistent anthropogenic carbon dioxide (CO 2 ) emissions have altered the natural balance of Earth’s carbon sources and sinks. These emissions are driven by a multitude of individual mobile and stationary point sources that combust fossil fuels, with urban areas accounting for more than 70% of anthropogenic emissions to the atmosphere. Natural point-source emissions are dominated by wildfires and persistent volcanic degassing.
RATIONALE
Comprehensive global measurements from space could help to more completely characterize anthropogenic and natural point-source emissions. In global carbon cycle models, anthropogenic point-source information comes from bottom-up emission inventories, whereas natural point-source information comes from a sparse in situ measurement network. Whereas clusters of urban CO 2 point-source plumes merge together, isolated point sources (e.g., remote power plants, cement production plants, and persistently degassing volcanoes) create localized plumes. Because turbulent mixing and diffusion cause rapid downwind dilution, they are challenging to detect and analyze. Point-source detection from space is complicated by signal dilution: The observed values of Δ X CO 2 (enhancement of the column-averaged dry-air CO 2 mole fraction) correspond to in situ CO 2 enhancements of 10-fold or higher. Space-based sensors that detect and quantify CO 2 in plumes from individual point sources would enable validation of reported inventory fluxes for power plants. These sensors would also advance the detectability of volcanic eruption precursors and improve volcanic CO 2 emission inventories.
RESULTS
Spaceborne measurements of atmospheric CO 2 using kilometer-scale data from NASA’s Orbiting Carbon Observatory-2 (OCO-2) reveal distinct structures caused by known anthropogenic and natural point sources, including megacities and volcanoes. Continuous along-track sampling across Los Angeles (USA) by OCO-2 at its ~2.25-km spatial resolution exposes intra-urban spatial variability in the atmospheric X CO 2 distribution that corresponds to the structure of the urban dome, which is detectable under favorable wind conditions. Los Angeles X CO 2 peaks over the urban core and decreases through suburban areas to rural background values more than ~100 km away. Enhancements of X CO 2 in the Los Angeles urban CO 2 dome observed by OCO-2 vary seasonally from 4.4 to 6.1 parts per million (ppm). We also detected isolated CO 2 plumes from the persistently degassing Yasur, Ambrym, and Aoba volcanoes (Vanuatu), corroborated by near-simultaneous sulfur dioxide plume detections by NASA’s Ozone Mapping and Profiler Suite. An OCO-2 transect passing directly downwind of Yasur volcano yielded a narrow filament of enhanced X CO 2 ( Δ X CO 2 ≈ 3.4 ppm), consistent with plume modeling of a CO 2 point source emitting 41.6 ± 19.7 kilotons per day (15.2 ± 7.2 megatons per year). These highest continuous volcanic CO 2 emissions are collectively dwarfed by about 70 fossil fuel–burning power plants on Earth, which each emit more than 15 megatons per year of CO 2 .
CONCLUSION
OCO-2’s sampling strategy was designed to characterize CO 2 sources and sinks on regional to continental and ocean-basin scales, but the unprecedented kilometer-scale resolution and high sensitivity enables detection of CO 2 from natural and anthropogenic localized emission sources. OCO-2 captures seasonal, intra-urban, and isolated plume signals. Capitalizing on OCO-2’s sensitivity, a much higher temporal resolution would capture anthropogenic emission signal variations from diurnal, weekly, climatic, and economic effects, and, for volcanoes, precursory emission variability. Future sampling strategies will benefit from a continuous mapping approach with the sensitivity of OCO-2 to systematically and repeatedly capture these smaller, urban to individual plume scales of CO 2 point sources.
OCO-2 detects urban CO 2 signals with unprecedented detail over Los Angeles
Individual “footprints” of OCO-2 X CO 2 data from early fall 2014 and summer 2015 over the city of Los Angeles strongly contrast with values over the distant, rural Antelope Valley. X CO 2 is the averaged dry-air molar CO 2 concentration between the spacecraft and Earth’s surface.
Thermal fluids in Iceland range in temperature from <10°C to >440°C and are dominated by water (>97mol%) with a chloride concentration from <10ppm to >20,000ppm. The isotope systematics of the fluids reveal many important features of the source(s) and transport properties of volatiles at this divergent plate boundary. Studies spanning over four decades have revealed a large range of values for δD (-131 to +3.3‰), tritium (-0.4 to +13.8 TU), δ¹⁸O (-20.8 to +2.3‰), ³He/⁴He (3.1 to 30.4 RA), δ¹¹B (-6.7 to +25.0‰), δ¹³C∑CO2 (-27.4 to +4.6‰), ¹⁴C∑CO2 (+0.6 to +118 pMC), δ¹³CCH4 (-52.3 to -17.8‰), δ¹⁵N (-10.5 to +3.0‰), δ³⁴S∑S-II (-10.9 to +3.4‰), δ³⁴SSO4 (-2.0 to +21.2‰) and δ³⁷Cl (-1.0 to +2.1‰) in both liquid and vapor phases. Based on this isotopic dataset, the thermal waters originate from meteoric inputs and/or seawater. For other volatiles, degassing of mantle-derived melts contributes to He, CO2 and possibly also to Cl in the fluids. Water-basalt interaction also contributes to CO2 and is the major source of H2S, SO4, Cl and B in the fluids. Redox reactions additionally influence the composition of the fluids, for example, oxidation of H2S to SO4 and reduction of CO2 to CH4. Air-water interaction mainly controls N2, Ar and Ne concentrations. The large range of many non-reactive volatile isotope ratios, such as δ³⁷Cl and ³He/⁴He, indicate heterogeneity of the mantle and mantle-derived melts beneath Iceland. In contrast, the large range of many reactive isotopes, such as δ¹³C∑CO2 and δ³⁴S∑S-II, are heavily affected by processes occurring within the geothermal systems, including fluid-rock interaction, depressurization boiling, and isotopic fractionation between secondary minerals and the aqueous and vapor species. Variations due to these geothermal processes may exceed differences observed among various crust and mantle sources, highlighting the importance and effects of chemical reactions on the isotope systematics of reactive elements.
The CO2 contents of olivine-hosted melt inclusions have previously been used to constrain the depth of magma chambers in basaltic systems. However, the vast majority of inclusions have CO2 contents which imply entrapment pressures that are significantly lower than those obtained from independent petrological barometers. Furthermore, a global database of melt inclusion compositions from low settings, indicates that the distribution of saturation pressures varies surprisingly little between mid-ocean ridges, ocean islands, and continental rift zones. 95% of the inclusions in the database have saturation pressures of 200 MPa or less, indicating that melt inclusion CO2 does not generally provide an accurate estimate of magma chamber depths. A model of the P-V-T-X evolution of olivine-hosted melt inclusions was developed so that the properties of the inclusion system could be tracked as the hosts follow a model P-T path. The models indicate that the principal control on the saturation of CO2 in the inclusion and the formation of vapor bubbles is the effect of postentrapment crystallization on the major element composition of the inclusions and how this translates into variation in CO2 solubility. The pressure difference between external melt and the inclusion is likely to be sufficiently high to cause decrepitation of inclusions in most settings. Decrepitation can account for the apparent mismatch between CO2-based barometry and other petrological barometers, and can also account for the observed global distribution of saturation pressures. Only when substantial postentrapment crystallization occurs can reconstructed inclusion compositions provide an accurate estimate of magma chamber depth.
We report new carbon dioxide (CO2) abundance and isotope data for 71 geothermal gases and fluids from both high-temperature (HT > 150 °C at 1 km depth) and low-temperature (LT < 150 °C at 1 km depth) geothermal systems located within neovolcanic zones and older segments of the Icelandic crust, respectively. These data are supplemented by CO2 data obtained by stepped heating of 47 subglacial basaltic glasses collected from the neovolcanic zones. The sample suite has been characterized previously for He–Ne (geothermal) and He–Ne–Ar (basalt) systematics (Füri et al., 2010), allowing elemental ratios to be calculated for individual samples. Geothermal fluids are characterized by a wide range in carbon isotope ratios (δ13C), from −18.8‰ to +4.6‰ (vs. VPDB), and CO2/3He values that span eight orders of magnitude, from 1 × 104 to 2 × 1012. Extreme geothermal values suggest that original source compositions have been extensively modified by hydrothermal processes such as degassing and/or calcite precipitation. Basaltic glasses are also characterized by a wide range in δ13C values, from −27.2‰ to −3.6‰, whereas CO2/3He values span a narrower range, from 1 × 108 to 1 × 1012. The combination of both low δ13C values and low CO2 contents in basalts indicates that magmas are extensively and variably degassed. Using an equilibrium degassing model, we estimate that pre-eruptive basaltic melts beneath Iceland contain ∼531 ± 64 ppm CO2 with δ13C values of −2.5 ± 1.1‰, in good agreement with estimates from olivine-hosted melt inclusions ( Metrich et al., 1991) and depleted MORB mantle (DMM) CO2 source estimates ( Marty, 2012). In addition, pre-eruptive CO2 compositions are estimated for individual segments of the Icelandic axial rift zones, and show a marked decrease from north to south (Northern Rift Zone = 550 ± 66 ppm; Eastern Rift Zone = 371 ± 45 ppm; Western Rift Zone = 206 ± 24 ppm). Notably, these results are model dependent, and selection of a lower δ13C fractionation factor will result in lower source estimates and larger uncertainties associated with the initial δ13C estimate. Degassing can adequately explain low CO2 contents in basalts; however, degassing alone is unlikely to generate the entire spectrum of observed δ13C variations, and we suggest that melt–crust interaction, involving a low δ13C component, may also contribute to observed signatures. Using representative samples, the CO2 flux from Iceland is estimated using three independent methods: (1) combining measured CO2/3He values (in gases and basalts) with 3He flux estimates ( Hilton et al., 1990), (2) merging basaltic emplacement rates of Iceland with pre-eruptive magma source estimates of ∼531 ± 64 ppm CO2, and (3) combining fluid CO2 contents with estimated regional fluid discharge rates. These methods yield CO2 flux estimates from of 0.2–23 × 1010 mol a−1, which represent ∼0.1–10% of the estimated global ridge flux (2.2 × 1012 mol a−1; Marty and Tolstikhin, 1998).
Carbon dioxide solubility and isotope fractionation data for a MORB composition at 1,200-1,400C and 5-20 kbar have been obtained using piston-cylinder apparatus and stepped-heating mass spectrometry. Carbon dioxide solubility in basalt melt at 5, 10 and 20 kbar is 0.15-0.17%, 0.45-0.51%, and 1.49%, respectively. Values for {Delta}Co{sub 2}(vap) - CO 2/3{sup {minus}} (basalt melt), obtained from the difference between the isotopic compositions for coexisting vapor and melt, vary from 1.8% to 2.2%. A review of measured and estimated values for carbon isotope fractionation between CO{sub 2} vapor and carbon dissolved in basic melts shows variation from 1.8% to 4.6%. Results of this study and other considerations favor relatively small equilibrium CO{sub 2} vapor melt fractionation factors around 2%.
Carbon dioxide solubility and isotope fractionation data for a MORB composition at 1200-1400°C and 5-20 kbar have been obtained using piston-cylinder apparatus and stepped-heating mass spectrometry. Carbon dioxide solubility in basalt melt at 5, 10, and 20 kbar is 0.15-0.17%, 0.45-0.51%, and 1.49%, respectively. Values for CO 2 (vap) - CO 2- 3 (basalt melt), obtained from the difference between the isotopic compositions of coexisting vapour and melt, vary from 1.8%. to 2.2%. A review of measured and estimated values for carbon isotope fractionation between CO 2 vapour and carbon dissolved in basic melts shows variation from 1.8%. to 4.6%. Results of this study and other considerations favour relatively small equilibrium CO 2 vapour melt fractionation factors around 2%.
We report a CO2 emission rate of 8500 metric tons per day (t d-1) for the summit of Kilauea Volcano, several times larger than previous estimates. It is based on three sets of measurements over 4 years of synchronous SO2 emission rates and volcanic CO2/SO2 concentration ratios for the summit correlation spectrometer (COSPEC) traverse. Volcanic CO2/SO2 for the traverse is representative of the global ratio for summit emissions. The summit CO2 emission rate is nearly constant, despite large temporal variations in summit CO2/SO2 and SO2 emission rates. Summit CO2 emissions comprise most of Kilauea's total CO2 output (~9000 t d-1). The bulk CO2 content of primary magma determined from CO2 emission and magma supply rate data is ~0.70 wt %. Most of the CO2 is present as exsolved vapor at summit reservoir depths, making the primary magma strongly buoyant. Turbulent mixing with resident reservoir magma, however, prevents frequent eruptions of buoyant primary magma in the summit region. CO2 emissions confirm that the magma supply enters the edifice through the summit reservoir. A persistent several hundred parts per million CO2 anomaly arises from the entry of magma into the summit reservoir beneath a square kilometer area east of Halemaumau pit crater. Since most of the CO2 in primary magma is degassed in the summit, the summit CO2 emission rate is an effective proxy for the magma supply rate. Both scrubbing of SO2 and solubility controls on CO2 and S in basaltic melt cause high CO2/SO2 in summit emissions and spatially uncorrelated distributions of CO2 and SO2 in the summit plume.
Isotope analyses for C, O, H and S from the Pine Creek tungsten mine are reported and studied in theoretical context for estimates of metamorphic P, T and fluid compositions. Quartz monzonite intruded thermally metamorphosed rocks and expelled and mobilized watery fluids that produced ore-bearing skarn. High-Mo scheelite was deposited during development of skarn, and redistributed as low-Mo scheelite on cooling of the skarn. Later fluids of unknown origin caused alteration of the skarn mineralogy to greenschist assemblages, and ultimately formed vugs now filled with zeolites. D/H data are interpreted as measuring the increasing role of meteoric water in the retrograde phases of metamorphism. -G.J.N.
The small but finite solubility of CO2 in granitic magmas under crustal conditions, together with the common occurrence of CO2 in likely magma source materials, suggests that granitic magmas will often be accompanied by a CO2-H2O fluid phase during their ascent in the crust. Polybaric and isobaric calculations have been made for model systems with varying total volatile content, initial CO2/H2O ratios, crystallization rates, and closed-system or open-system conditions. The calculations demonstrate that the presence of CO2 in an evolving magma system can result in greatly differing values of H2O activity (and hence H2O content, phase equilibria, and physical properties of the magma). Specifically, if the mass ratio CO2/H2O is ≥0.4 and the initial mass ratio of total volatiles to silicate magma is ≥0.05, then, if little or no loss of the fluid phase occurs during magma evolution, the activity of H2O will remain nearly constant. This is in strong contrast to all other possible cases in which the activity of H2O increases rapidly with decreasing pressure and (or) anhydrous phase crystallization, invariably reaching a value of unity. It is also demonstrated that if CO2 is present in a fluid phase in the magma source region, then there will be a fluid present throughout the evolutionary history of the magma. The presence of fluid bubbles in the magma should considerably alter many properties of the magma system such as heat transfer, mass transfer, and viscosity.
The development of a second-order integral model for a round turbulent buoyant
jet is reported based on new experimental data on turbulent mass and momentum
transport. The mean and turbulent characteristics of a round vertical buoyant jet
covering the full range from jets to plumes were investigated using a recently developed
combined digital particle image velocimetry (DPIV) and planar laser-induced
fluorescence (PLIF) system. The system couples the two well-known techniques to
enable synchronized planar measurements of flow velocities and concentrations in
a study area. The experimental results conserved the mass and momentum fluxes
introduced at the source accurately with closure errors of less than 5%. The momentum
flux contributed by turbulence and streamwise pressure gradient was determined
to be about 10% of the local mean momentum flux in both jets and plumes. The
turbulent mass flux, on the other hand, was measured to be about 7.6% and 15%
of the mean mass flux for jets and plumes respectively. While the velocity spread
rate was shown to be independent of the flow regime, the concentration-to-velocity
width ratio λ varied from 1.23 to 1.04 during the transition from jet to plume. Based
on the experimental results, a refined second-order integral model for buoyant jets
that achieves the conservation of total mass and momentum fluxes is proposed. The
model employs the widely used entrainment assumption with the entrainment coefficient
taken to be a function of the local Richardson number. Improved prediction
is achieved by taking into account the variation of turbulent mass and momentum
fluxes. The variation of turbulent mass flux is modelled as a function of the local
Richardson number. The turbulent momentum flux, on the other hand, is treated
as a fixed percentage of the local mean momentum flux. In addition, unlike most
existing integral models that assume a constant concentration-to-velocity width ratio,
the present model adopts a more accurate approach with the ratio expressed as a
function of the local Richardson number. As a result, smooth transition of all relevant
mean and turbulent characteristics from jet to plume is predicted, which is in line
with the underlying physical processes.
We examine models for batch-equilibrium and fractional-equilibrium degassing of CO2 from magma at Kilauea Volcano. The models are based on 1.(1) the concept of two-stage degassing of CO2 from magma supplied to the summit chamber,2.(2) C isotope data for CO2 in eruptive and noneruptive (quiescent) gases from Kilauea and3.(3) data for the isotopic fractionation of C between CO2 and C dissolved in tholeiitic basalt melt. The results of our study indicate that 1.(1) both eruptive and noneruptive degassing of CO2 most closely approach a batch equilibrium process,2.(2) the δ13C of parental magma supplied to the summit chamber is in the range −4.1 to−3.4‰ and3.(3) the δ13C of melt after summit chamber degassing is in the range −7 to −8‰, depending upon the depth of equilibration. We also present δ13C data for CO2 in eruptive gases from the current East Rift Zone eruption. These are the first C isotope data for CO2 in high-temperature (>900°C) eruptive gases from Kilauea; they have a mean δ13C value of −7.82 ± 0.24‰ and are similar to those predicted for the melt after summit chamber degassing. The minor role played by fractional degassing of ascending magma at Kilauea means that exsolved CO2 tends to remain entrained in and coherent with its host melt during ascent from both mantle source regions and crustal magma reservoirs. This has important implications for magma dynamics at Kilauea.
Isotope fractionation of carbon between CO2 and carbon dissolved in a tholeiitic magma measured in the range 1120–1280 C, 7.0–8.4 Kb varies from 4.6 to 4 in favor of CO2. These results make possible to explain all deep seated 13C values from a restricted range of primary mantle 13C concentrations. They also suggest that carbon could be dissolved in basaltic magmas in a reduced form.
To document the characteristics of volatiles in the terrestrial mantle, the abundances and the isotopic ratios of carbon, nitrogen, helium, and argon have been analyzed in 45 mid-ocean ridge basalts (MORB) glasses from the Mid-Atlantic Ridge between 24°N and 36°N, the East Pacific Rise at 21°N, 13°N, and 17–19°S, the Red Sea (18–20°N), the Indian Ocean near the Triple Junction, and the central North Fiji basin. Gases were extracted by crushing and subsequently were split for purification and analysis. Static mass spectrometry was used for N, He, and Ar, and conventional dynamic mass spectrometry was used for C. The data confirm the occurrence of near-constant He isotope ratios (3He/4He = 8.53 ± 0.79 Ra; n = 36) and C isotope ratios (δ13C = −5.2 ± 0.7‰ vs. PDB; n = 21), and of a light nitrogen component in the convective mantle. Overall, the δ15N signature of MORB (mean δ15N = −3.3 ± 1.0‰ vs. ATM, for samples with 40Ar/36Ar > 1000; n = 19) does not drastically differ from that of diamonds, some of which being presumably ≥3 Ga, and is thought to represent the nitrogen isotopic ratio of the asthenospheric mantle. A common mantle source for diamond-bearing magmas and MORB magmas is unlikely, and this similarity may imply either active exchange of volatiles between the respective mantle sources or homogeneous distribution of nitrogen isotopes in these sources during most of Earth’s history. Variations of the 4He/40Ar∗ ratios as well as 40Ar/36Ar ratios are consistent with fractional crystallization–assimilation–degassing taking place in the depth range of 3 to 6 km. The corrected average C/N of the MORB mantle is 535 ± 224, significantly higher than potential cosmochemical and geochemical end-members. C/He and C/N ratios corrected for fractional crystallization–assimilation–degassing fractionation increase with the degree of MORB enrichment (e.g., increasing K2O/TiO2) and are thought to reflect carbon heterogeneities in the mantle source, as a result of fractional recycling of a (fluid?) component extremely enriched in carbon (C/N > 3000). The N/3He ratios are less variable than the C/3He ratios, suggesting limited recycling of nitrogen. Such limited recycling is required to preserve a N isotope ratio in the convective mantle distinct from that of the atmosphere–hydrosphere sediments. Overall, neon, argon, nitrogen, and carbon abundances in the mantle appear to be chondritic, rather than solar, although the neon isotopic signature of the mantle indicates contribution of a solar component. This apparent discrepancy may reflect mixing between a solar-type component mostly seen at present in light rare gases and a chondritic-type component and has strong implications for the origin of terrestrial matter and the processes of their accretion.
Fifty samples of rural air collected near the Pacific coast of North America have been analysed for carbon dioxide reporting, in addition to concentration in air, the isotopic abundances of C13 and O18. A correlation observed for all samples between C13 isotope abundance and concentration in air can be explained by assuming an initial composition for atmospheric carbon dioxide of 0.031 volume per cent in air, ratio−7.0 per mil., to which is added carbon dioxide of plant origin with a ratio of approximately −23 per mil. Minimum concentrations and associated carbon isotope ratios at different stations show very little variation (0.0307–0.0316 per cent, −6.7 to −7.4 per mil) and are believed to be representative of Pacific maritime air. Oxygen isotope abundances are approximately the same as for carbon dioxide in chemical equilibrium with average ocean water, but individual samples show variations which generally do not correlate with changes in concentration in air and are as yet unexplained.
For 30 years, the correlation spectrometer (COSPEC) has been the principal tool for remote monitoring of volcanic SO2 fluxes. During this time, the instrument has played a prominent role in volcanic hazard assessment. COSPEC data also underpin estimates of the global volcanic SO2 flux to the atmosphere. Though innovative for its time, COSPEC is now outdated in several respects. Here we report the first measurements with a potential replacement, using a low cost, miniature, ultraviolet fibre-optic differential optical absorption spectrometer (mini-DOAS). Field experiments were conducted at Masaya Volcano (Nicaragua) and Soufrière Hills Volcano (Montserrat). The mini-DOAS was operated from a road vehicle and helicopter, and from a fixed position on the ground, indicating fluxes of ∼4 and 1 kg s−1 at Masaya Volcano and Soufrière Hills Volcano, respectively. Side-by-side observations with a COSPEC on Montserrat indicate a comparable sensitivity but the mini-DOAS offers several advantages, including the collection of broadband ultraviolet spectra. It has immense potential for geochemical surveillance at volcanoes worldwide.
The emissions of CO 2 and other volatiles from the world's subaerial volcanoes
- T P Fischer
- S Arellano
- S Carn
- A Aiuppa
- P Allard
- T Lopez
- H Shinohara
- P J Kelly
- C Werner
- C Cardelini
- G Chiodini
Fischer TP, Arellano S, Carn S, Aiuppa A, Allard P, Lopez T, Shinohara H, Kelly PJ, Werner C, Cardelini C, Chiodini G (2019)
The emissions of CO 2 and other volatiles from the world's
subaerial volcanoes. Sci Rep 9:18716. https:// doi. org/ 10. 1038/
s41598-41019-54682-41591
Volcanic degassing: processes and impact
- C Oppenheimer
- T P Fischer
- B Scaillet
Oppenheimer C, Fischer TP, Scaillet B (2014) Volcanic degassing:
processes and impact. Treatise on Geochemistry (second edition).
4, the crust p.111-179 https:// doi. org/ 10. 1016/ B1978-1010-1008-095975-095977. 000304-095971
Third time's the charm for Iceland's Fagradalsfjall
- K Kornei
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