Scrubbing masks magmatic degassing during repose at Cascade-Range and Aleutian-Arc volcanoes

Symonds, Robert B.; Janik, C.J.; Evans, William C.; Ritchie, B.E.; Counce, D.; Poreda, Robert J.; Iven, Mark

doi:10.3133/ofr03435

Cited by 19 publications

(37 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The equilibrium chlorine isotope fractionation between HCl gas and Cl − is ∼ +1.5h between 50 and 100 • C (Schauble et al, 2003), therefore even small amounts of degassing can explain the high δ 37 Cl values observed in the thermal springs. Symonds et al (2003) also propose a two-step "scrubbing" process within Cascade arc volcanoes by which HCl is removed by deep thermal water (150-350 • C) and then by shallow meteoric water. It is conceivable that the exsolved HCl progressively fractionates as 35 Cl is preferentially "scrubbed out" in the deeper reservoirs and eventually the 37 Clenriched vapor mixes with the shallow ground-waters.…”

Section: Degassing Of Chlorine and Implications For Magmatic Processesmentioning

confidence: 98%

Tracing chlorine sources of thermal and mineral springs along and across the Cascade Range using halogen concentrations and chlorine isotope compositions

Cullen

Barnes

Hurwitz

et al. 2015

Earth and Planetary Science Letters

View full text Add to dashboard Cite

Editor: T.A. Mather Keywords: halogen stable isotope chlorine isotope Cascade Range thermal springs hydrothermalIn order to provide constraints on the sources of chlorine in spring waters associated with arc volcanism, the major/minor element concentrations and stable isotope compositions of chlorine, oxygen, and hydrogen were measured in 28 thermal and mineral springs along the Cascade Range in northwestern USA. Chloride concentrations in the springs range from 64 to 19,000 mg/L and δ 37 Cl values range from +0.2h to +1.9h (average = +1.0 ± 0.4h), with no systematic variation along or across the arc, nor correlations with their presumed underlying basement lithologies. Additionally, nine geochemically wellcharacterized lavas from across the Mt. St. Helens/Mt. Adams region of the Cascade Range (Leeman et al., 2004(Leeman et al., , 2005 were analyzed for their halogen concentrations and Cl isotope compositions. In the arc lavas, Cl and Br concentrations from the volcanic front are higher than in lavas from the forearc and backarc. F and I concentrations progressively decrease from forearc to backarc, similar to the trend documented for B in most arcs. δ 37 Cl values of the lavas range from −0.1 to +0.8h (average = +0.4 ±0.3h). Our results suggest that the predominantly positive δ 37 Cl values observed in the springs are consistent with water interaction with underlying 37 Cl-enriched basalt and/or altered oceanic crust, thereby making thermal spring waters a reasonable proxy for the Cl isotope compositions of associated volcanic rocks in the Cascades. However, waters with δ 37 Cl values > + 1.0h also suggest additional contributions of chlorine degassed from cooling magmas due to subsurface vapor-liquid HCl fractionation in which Cl is lost to the aqueous fluid phase and 37 Cl is concentrated in the ascending magmatic HCl vapor. Future work is necessary to better constrain Cl isotope behavior during volcanic degassing and fluid-rock interaction in order to improve volatile flux estimates through subduction zones.

show abstract

Section: Degassing Of Chlorine and Implications For Magmatic Processesmentioning

confidence: 98%

Tracing chlorine sources of thermal and mineral springs along and across the Cascade Range using halogen concentrations and chlorine isotope compositions

Cullen

Barnes

Hurwitz

et al. 2015

Earth and Planetary Science Letters

View full text Add to dashboard Cite

show abstract

“…Large‐scale scrubbing of SO 2 is often called on to maintain the high C/S ratios in volcanic environments prior to or during eruptions [ Doukas and Gerlach , 1995; Symonds et al , 2001; Gerlach et al , 2008; Werner et al , 2008]. In this scenario, magmatic gases originally enriched in CO 2 and SO 2 preferentially lose sulfur either to magmatic‐hydrothermal brines or mineralization within the volcanic edifice, or near the surface to groundwater or lakes [ Symonds et al , 2001, 2003]. In a report on several volcanic systems in the Cascades and Alaska, Symonds et al [2003] discuss these possibilities as primary (within the volcanic edifice or deeper) and secondary (near the surface) scrubbing, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…At basaltic volcanoes, the C/S molar ratio in volcanic gas (typically derived from CO 2 /SO 2 measurements in plumes) has been observed to increase in the hours to weeks before eruptions, a pattern interpreted as the geochemical signature of mafic, CO 2 ‐rich magmas intruding from lower crustal reservoirs [ Aiuppa et al , 2006, 2009]. At “wet” volcanoes, typical of many found in the Cascade and Alaskan volcanic arcs [ Symonds et al , 2003], scrubbing of volcanic SO 2 can also cause the C/S ratio to exceed typical magmatic values, complicating the interpretation of this parameter [ Doukas and Gerlach , 1995; Symonds et al , 2001, 2003; Gerlach et al , 2008; Werner et al , 2011].…”

Section: Introductionmentioning

confidence: 99%

Deep magmatic degassing versus scrubbing: Elevated CO₂emissions and C/S in the lead‐up to the 2009 eruption of Redoubt Volcano, Alaska

Werner

Evans

Kelly

et al. 2012

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

[1] We report CO 2, SO 2 , and H 2 S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska. CO 2 emission rates up to 9018 t/d and C/S ratios ≥30 measured in the months prior to the eruption were critical for fully informed forecasting efforts. Observations of icemelt rates, meltwater discharge, and water chemistry suggest that surface waters represented drainage from surficial, perched reservoirs of condensed magmatic steam and glacial meltwater. These fluids scrubbed only a few hundred tonnes/day of SO 2 , not the >2100 t/d SO 2 expected from degassing of magma in the mid-to upper crust (3-6.5 km), where petrologic analysis shows the final magmatic equilibration occurred. All data are consistent with upflow of a CO 2 -rich magmatic gas for at least 5 months prior to eruption, and minimal scrubbing of SO 2 by near-surface groundwater. The high C/S ratios observed could reflect bulk degassing of mid-crustal magma followed by nearly complete loss of SO 2 in a deep magmatic-hydrothermal system. Alternatively, high C/S ratios could be attributed to decompressional degassing of low silica andesitic magma that intruded into the mid-crust in the 5 months prior to eruption, thereby mobilizing the preexisting high silica andesite magma or mush in this region. The latter scenario is supported by several lines

show abstract

“…The resulting gas-water-rock interactions cause partitioning of water-soluble species (S, halogens) into aqueous solutions, and irreversibly modify the composition of the primary magmatic gas phase. Quantitative assessment of scrubbing is, therefore, essential for interpreting mechanisms and evolution of volcanichydrothermal unrests (Doukas and Gerlach, 1995;Gerlach et al, 2008;Ilyinskaya et al, 2015;Symonds et al, 2001Symonds et al, , 2003Werner et al, 2008Werner et al, , 2012Shinohara et al, 2015). The mechanism of magmatic gas scrubbing by hydrothermal systems was introduced in the fifties (White, 1957), but it was only in the 1990s that scrubbing was invoked as a most important process to explain the anomalous low fluxes of magmatic SO 2 and HCl observed at many volcanoes worldwide, both before and after eruptions (Doukas and Gerlach, 1995;Reed, 1997).…”

Section: Introductionmentioning

confidence: 99%

Reaction path models of magmatic gas scrubbing

et al. 2016

View full text Add to dashboard Cite

Gas-water-rock reactions taking place within volcano-hosted hydrothermal systems scrub reactive, water-soluble species (sulfur, halogens) from the magmatic gas phase, and as such play a major control on the composition of surface gas manifestations. A number of quantitative models of magmatic gas scrubbing have been proposed in the past, but no systematic comparison of model results with observations from natural systems has been carried out, to date. Here, we present the results of novel numerical simulations, in which we initialized models of hydrothermal gaswater-rock at conditions relevant to Icelandic volcanism. We focus on Iceland as an example of a "wet" volcanic region where scrubbing is widespread. Our simulations were performed (using the EQ3/6 software package) at shallow (temperature b 106°C; low-T model runs) and deep hydrothermal reservoir (200-250°C; high-T model runs) conditions. During the simulations, a high-temperature magmatic gas phase was added stepwise to an initial meteoric water, in the presence of a dissolving aquifer rock. At each step, the chemical compositions of coexisting aqueous solution and gas phase were returned by the model. The model-derived aqueous solutions have compositions that describe the maturation path of hydrothermal fluids, from immature, acidic Mg-rich waters, toward Na-Cl-rich mature hydrothermal brines. The modeled compositions are in fair agreement with measured compositions of natural thermal waters and reservoir fluids from Iceland. We additionally show that the composition of the modelgenerated gases is strongly temperature-dependent, and ranges from CO 2(g) -dominated (for temperatures ≤80°C) to H 2 O (g) -dominated (and more H 2 S (g) rich) for temperatures N 100°C. We find that this range of model gas compositions reproduces well the (H 2 O-CO 2 -S TOT ) compositional range of reservoir waters and surface gas emissions in Iceland. From this validation of the model in an extreme end-member environment of high scrubbing, we conclude that EQ3/6-based reaction path simulations offer a realistic representation of gas-water-rock interaction processes occurring underneath active magmatic-hydrothermal systems.

show abstract

Scrubbing masks magmatic degassing during repose at Cascade-Range and Aleutian-Arc volcanoes

Abstract: Between 1992 and 1998, we sampled gas discharges from ≤173°C fumaroles and springs at 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA) including

Cited by 19 publications

References 37 publications

Tracing chlorine sources of thermal and mineral springs along and across the Cascade Range using halogen concentrations and chlorine isotope compositions

Tracing chlorine sources of thermal and mineral springs along and across the Cascade Range using halogen concentrations and chlorine isotope compositions

Deep magmatic degassing versus scrubbing: Elevated CO₂emissions and C/S in the lead‐up to the 2009 eruption of Redoubt Volcano, Alaska

Reaction path models of magmatic gas scrubbing

Contact Info

Product

Resources

About

Scrubbing masks magmatic degassing during repose at Cascade-Range and Aleutian-Arc volcanoes

Abstract: Between 1992 and 1998, we sampled gas discharges from ≤173°C fumaroles and springs at 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA) including

Cited by 19 publications

References 37 publications

Tracing chlorine sources of thermal and mineral springs along and across the Cascade Range using halogen concentrations and chlorine isotope compositions

Tracing chlorine sources of thermal and mineral springs along and across the Cascade Range using halogen concentrations and chlorine isotope compositions

Deep magmatic degassing versus scrubbing: Elevated CO2emissions and C/S in the lead‐up to the 2009 eruption of Redoubt Volcano, Alaska

Reaction path models of magmatic gas scrubbing

Contact Info

Product

Resources

About

Deep magmatic degassing versus scrubbing: Elevated CO₂emissions and C/S in the lead‐up to the 2009 eruption of Redoubt Volcano, Alaska