The currently available data set of S–Cl–F abundances in volcanic gas plumes and high-temperature fumarolic gas samples from basaltic volcanism is reviewed here in the attempt to derive constraints ...on the modes of halogen degassing from mafic silicate melts. Apart from large volcano-to-volcano variations, reflecting remarkable differences in volatile abundances in the source magmas, each of the explored volcanoes displays large changes of SO
2/HCl and SO
2/HF ratios with the style of volcanic activity, with HCl/HF staying fairly constant. Halogen abundances are low and SO
2/HCl and SO
2/HF are high when fresh (volatile-rich) magmas sustain degassing, as during explosive eruptions, at the onset of eruptive cycles, or shortly before paroxysmal events. Low SO
2/HCl and SO
2/HF ratios are instead characteristic of late stages of volcanic degassing, typically being observed in the concluding stages of basaltic eruptions, or during periods of reduced magma supply at persistently degassing volcanoes. These observations are taken as evidence of halogens being less keen to enter the gas phase (relative to S) during degassing of basaltic magmas; and quantitatively interpreted in light of a Rayleigh-type open-system degassing model. The model, though simple, quantitatively reproduces the range of volcanic gas compositions observed at basaltic volcanoes worldwide, and allows prediction of vapour/melt partitioning contrasts of factors ~
9 and ~
36 for the volatile couples S–Cl and S–F, respectively. These predictions require validation from appropriately designed experiments of halogen partitioning between magmatic vapours and silicate melts over a range of
P–
T–
X conditions.
Identification of unambiguous signals of volcanic unrest is crucial in hazard assessment. Processes leading to phreatic and phreatomagmatic eruptions remain poorly understood, inhibiting effective ...eruption forecasting. Our 5‐year gas record from Poás volcano, combined with geophysical data, reveals systematic behavior associated with hydrothermal‐magmatic eruptions. Three eruptive episodes are covered, each with distinct geochemical and geophysical characteristics. Periods with larger eruptions tend to be associated with stronger excursions in monitoring data, particularly in SO2/CO2 and SO2 flux. The explosive 2017 phreatomagmatic eruption was the largest eruption at Poás since 1953 and was preceded by dramatic changes in gas and geophysical parameters. The use of drones played a crucial role in gas monitoring during this eruptive period. Hydrothermal sealing and volatile accumulation, followed by top‐down reactivation of a shallow previously emplaced magma body upon seal failure, are proposed as important processes leading to and contributing to the explosivity of the 2017 eruption.
Plain Language Summary
High‐frequency monitoring of phreatic eruptions shows that clear precursory signals often exist to these dangerous explosive events. We interrogate the processes that lead to phreatic eruptions and investigate the intricate connections between magma intrusions and the hydrothermal systems that they feed.
Key Points
Three eruptive phases are characterized in detail through five years of high‐frequency monitoring
We identify and discuss precursors to phreatic and phreatomagmatic eruptions
Enhanced hydrothermal sealing can lead to larger eruptions and top‐down remobilization of magma
Ocean acidification is one of the most dramatic effects of the massive atmospheric release of anthropogenic carbon dioxide (CO
2
) that has occurred since the Industrial Revolution, although its ...effects on marine ecosystems are not well understood. Submarine volcanic hydrothermal fields have geochemical conditions that provide opportunities to characterise the effects of elevated levels of seawater CO
2
on marine life in the field. Here, we review the geochemical aspects of shallow marine CO
2
-rich seeps worldwide, focusing on both gas composition and water chemistry. We then describe the geochemical effects of volcanic CO
2
seepage on the overlying seawater column. We also present new geochemical data and the first synthesis of marine biological community changes from one of the best-studied marine CO
2
seep sites in the world (off Vulcano Island, Sicily). In areas of intense bubbling, extremely high levels of pCO
2
(> 10,000 μatm) result in low seawater pH (< 6) and undersaturation of aragonite and calcite in an area devoid of calcified organisms such as shelled molluscs and hard corals. Around 100–400 m away from the Vulcano seeps the geochemistry of the seawater becomes analogous to future ocean acidification conditions with dissolved carbon dioxide levels falling from 900 to 420 μatm as seawater pH rises from 7.6 to 8.0. Calcified species such as coralline algae and sea urchins fare increasingly well as sessile communities shift from domination by a few resilient species (such as uncalcified algae and polychaetes) to a diverse and complex community (including abundant calcified algae and sea urchins) as the seawater returns to ambient levels of CO
2
. Laboratory advances in our understanding of species sensitivity to high CO
2
and low pH seawater, reveal how marine organisms react to simulated ocean acidification conditions (e.g., using energetic trade-offs for calcification, reproduction, growth and survival). Research at volcanic marine seeps, such as those off Vulcano, highlight consistent ecosystem responses to rising levels of seawater CO
2
, with the simplification of food webs, losses in functional diversity and reduced provisioning of goods and services for humans.
Volcanic eruptions involving interaction with water are amongst the most violent and unpredictable geologic phenomena on Earth. Phreatic eruptions are exceptionally difficult to forecast by ...traditional geophysical techniques. Here we report on short-term precursory variations in gas emissions related to phreatic blasts at Poás volcano, Costa Rica, as measured with an in situ multiple gas analyzer that was deployed at the edge of the erupting lake. Gas emitted from this hyper-acid crater lake approaches magmatic values of SO2/CO2 1–6 days prior to eruption. The SO2 flux derived from magmatic degassing through the lake is measureable by differential optical absorption spectrometry (sporadic campaign measurements), which allows us to constrain lake gas output and input for the major gas species during eruptive and non-eruptive periods. We can further calculate power supply to the hydrothermal system using volatile mass balance and thermodynamics, which indicates that the magmatic heat flux into the shallow hydrothermal system increases from ∼27 MW during quiescence to ∼59 MW during periods of phreatic events. These transient pulses of gas and heat from the deeper magmatic system generate both phreatic eruptions and the observed short-term changes in gas composition, because at high gas flux scrubbing of sulfur by the hydrothermal system is both kinetically and thermodynamically inhibited whereas CO2 gas is always essentially inert in hyperacid conditions. Thus, the SO2/CO2 of lake emissions approaches magmatic values as gas and power supply to the sub-limnic hydrothermal system increase, vaporizing fluids and priming the hydrothermal system for eruption. Our results suggest that high-frequency real-time gas monitoring could provide useful short-term eruptive precursors at volcanoes prone to phreatic explosions.
•Changes in volcanic lake gas emissions precede phreatic eruptions.•First identified short-term precursor to phreatic eruptions.•Sulfur scrubbing can be negligible in hyper-acid volcanic lake environment.•Gas flux measurements allow quantification of hydrothermal system energy budget.•Transient pulses of magmatic gas cause phreatic eruptions.
Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved ...in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2‐rich gas (CO2/Stotal > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur‐rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is ~8–10 km deep, whereas the shallow magmatic gas source is at ~3–5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H2S/SO2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (>3000 T/d SO2 and H2S/SO2 > 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H2S/SO2 < 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high‐temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity.
Key Points
A gas composition precursor to eruptions is identified
Changes in gas compositions are associated with transitions in eruptive processes
Magma depth and volume are constrained
We report on the results of an extensive geochemical survey of fluids released in the Vardar zone (central‐western Serbia), a mega‐suture zone at the boundary between Eurasia and Africa plates. ...Thirty‐one bubbling gas samples are investigated for their chemical and isotopic compositions (He, C, Ar) and cluster into three distinct groups (CO2‐dominated, N2‐dominated, and CH4‐dominated) based on the dominant gas species. The measured He isotope ratios range from 0.08 to 1.19 Ra (where Ra is the atmospheric ratio), and reveal for the first time the presence of a minor (<20%) but detectable regional mantle‐derived component in Serbia. δ13C values range from −20.2‰ to −0.1‰ (versus PDB), with the more negative compositions observed in N2‐dominated samples. The carbon‐helium relationship indicates that these negative δ13C compositions could be due to isotopic fractionation processes during CO2 dissolution into groundwater. In contrast, CO2‐rich samples reflect mixing between crustal and mantle‐derived CO2. Our estimated mantle‐derived He flux (9.0 × 109 atoms m−2 s−1) is up to 2 orders of magnitude higher than the typical fluxes in stable continental areas, suggesting a structural/tectonic setting favoring the migration of deep‐mantle fluids through the crust.
Key Points
Chemical and isotopic composition of natural gas manifestations along the Serbian Vardar zone are controlled by mixing processes and fraction during water‐gas‐rock interactions in shallow crustal layers
Mantle‐derived He flux of 2 orders of magnitude higher than normally found in stable continental areas are estimated
Mantle volatiles and heat are sourced directly from the mantle supporting the asthenosphere up‐rise and delamination processes at the mantle‐crust boundary recognized in the studied area
Volcanoes with multiple summit vents present a methodological challenge for determining vent-specific gas emissions. Here, using a novel approach combining multiple ultraviolet cameras with ...synchronous aerial measurements, we calculate vent-specific gas compositions and fluxes for Stromboli volcano. Emissions from vent areas are spatially heterogeneous in composition and emission rate, with the central vent area dominating passive emissions, despite exhibiting the least explosive behaviour. Vents exhibiting Strombolian explosions emit low to negligible passive fluxes and are CO
-dominated, even during passive degassing. We propose a model for the conduit system based on contrasting rheological properties between vent areas. Our methodology has advantages for resolving contrasting outgassing dynamics given that measured bulk plume compositions are often intermediate between those of the distinct vent areas. We therefore emphasise the need for a vent-specific approach at multi-vent volcanoes and suggest that our approach could provide a transformative advance in volcano monitoring applications.
The mild activity of basaltic volcanoes is punctuated by violent explosive eruptions that occur without obvious precursors. Modelling the source processes of these sudden blasts is challenging. Here, ...we use two decades of ground deformation (tilt) records from Stromboli volcano to shed light, with unprecedented detail, on the short-term (minute-scale) conduit processes that drive such violent volcanic eruptions. We find that explosive eruptions, with source parameters spanning seven orders of magnitude, all share a common pre-blast ground inflation trend. We explain this exponential inflation using a model in which pressure build-up is caused by the rapid expansion of volatile-rich magma rising from depth into a shallow (<400 m) resident magma conduit. We show that the duration and amplitude of this inflation trend scales with the eruption magnitude, indicating that the explosive dynamics obey the same (scale-invariant) conduit process. This scale-invariance of pre-explosion ground deformation may usher in a new era of short-term eruption forecasting.
Halogens in volcanic systems Aiuppa, A.; Baker, D.R.; Webster, J.D.
Chemical geology,
06/2009, Letnik:
263, Številka:
1
Journal Article
Recenzirano
The transport, degassing and atmospheric release of halogens from active volcanism on Earth have been the focus of increasing interest over the last few decades, and have recently been the subject of ...the 1st workshop on “
Halogens in volcanic systems and their environmental impacts” that was held in December of 2007 at Yosemite Lodge in Yosemite National Park, California. As an introduction to this Chemical Geology special issue, collecting contributions from many of the participants at the workshop, we review here recent advances in this field, including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems. We discuss previous research on several aspects of halogen geochemistry, including halogen abundances in the mantle and magmas on Earth; the effects of halogens on phase equilibria and melt viscosities; their partitioning between melt and fluid phase(s) upon decompression, cooling and crystallisation of magmas in the Earth's crust; and their final atmospheric release as volcanic gases. The role of halogens in the genesis of hydrothermal systems and in the transport of ore-forming metals is also reviewed, and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere, and their consequent impacts. In spite of these recent advancements, our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary, and the key questions that require answers from future research are summarised in our conclusions.
This work presents a new database of SO2 and CO2 fluxes from the Southern Central American Volcanic Arc (SCAVA) for the period 2015–2016. We report ∼300 SO2 flux measurements from 10 volcanoes and ...gas ratios from 11 volcanoes in Costa Rica and Nicaragua representing the most extensive available assessment of this ∼500 km arc segment. The SO2 flux from SCAVA is estimated at 6,240 ± 1,150 T/d, about a factor of three higher than previous estimations (1972–2013). We attribute this increase in part to our more complete assessment of the arc. Another consideration in interpreting the difference is the context of increased volcanic activity, as there were more eruptions in 2015–2016 than in any period since ∼1980. A potential explanation for increased degassing and volcanic activity is a change in crustal stress regime (from compression to extension, opening volcanic conduits) following two large (Mw > 7) earthquakes in the region in 2012. The CO2 flux from the arc is estimated at 22,500 ± 4,900 T/d, which is equal to or greater than estimates of C input into the SCAVA subduction zone. Time‐series data sets for arc degassing need to be improved in temporal and spatial coverage to robustly constrain volatile budgets and tectonic controls. Arc volatile budgets are strongly influenced by short‐lived degassing events and arc systems likely display significant short‐term variations in volatile output, calling for expansion of nascent geochemical monitoring networks to achieve spatial and temporal coverage similar to traditional geophysical networks.
Plain Language Summary
We show that volcanoes in Central America are more active now than any time in the scientific record, and explore possible causes.
Key Points
We present an extensive new data set for Central American volcanic gas emission rates
Higher gas fluxes are observed for 2015–2016 than in previous studies, calling for expansion of gas monitoring networks
Higher gas fluxes are related to increased arc‐wide volcanic activity and may be related to megathrust earthquakes
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