Where is the Hot Rock and Where is the Ground Water – Using CSAMT to Map Beneath and Around Mount St. Helens

Wynn, Jeff; Mosbrucker, Adam R.; Pierce, Herbert A.; Spicer, Kurt R.

doi:10.2113/jeeg21.2.79

Cited by 25 publications

(10 citation statements)

References 22 publications

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“…Indeed, zones of elevated electrical conductivity have been detected below numerous volcanoes, including Vesuvius (Manzella et al 2004), the Campi Flegrei (Gresse et al 2018;Troiano et al 2014), Mt. St. Helens (Wynn et al 2016), Yellowstone (Kelbert et al 2012), the Altiplano Puna volcanic complex (Comeau et al 2015), Merapi (Müller and Haak 2004;Commer et al 2006), Mt. Unzen (Srigutomo et al 2008), Mt.…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Electrical conductivity of HCl-bearing aqueous fluids to 700 ºC and 1 GPa

Klumbach

Keppler

2020

Contrib Mineral Petrol

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Subsurface magmatic–hydrothermal systems are often associated with elevated electrical conductivities in the Earthʼs crust. To facilitate the interpretation of these data and to allow distinguishing between the effects of silicate melts and fluids, the electrical conductivity of aqueous fluids in the system H2O–HCl was measured in an externally heated diamond anvil cell. Data were collected to 700 °C and 1 GPa, for HCl concentrations equivalent to 0.01, 0.1, and 1 mol/l at ambient conditions. The data, therefore, more than double the pressure range of previous measurements and extend them to geologically realistic HCl concentrations. The conductivities $$\sigma$$ σ (in S/m) are well reproduced by a numerical model log $$\sigma$$ σ = −2.032 + 205.8 T−1 + 0.895 log c + 3.888 log $$\rho$$ ρ + log$$\Lambda_{0}$$ Λ 0 (T,$$\rho$$ ρ ), where T is the temperature in K, c is the HCl concentration in wt. %, and $$\rho$$ ρ is the density of pure water at the corresponding pressure and temperature conditions. $$\Lambda_{0}$$ Λ 0 (T,$$\rho$$ ρ ) is the limiting molar conductivity (in S cm2 mol−1) at infinite dilution, $$\Lambda_{0}$$ Λ 0 (T,$$\rho$$ ρ ) = 2550.14 − 505.10$$\rho$$ ρ − 429,437 T−1. A regression fit of more than 800 data points to this model yielded R2 = 0.95. Conductivities increase with pressure and fluid densities due to an enhanced dissociation of HCl. However, at constant pressures, conductivities decrease with temperature because of reduced dissociation. This effect is particularly strong at shallow crustal pressures of 100–200 MPa and can reduce conductivities by two orders of magnitude. We, therefore, suggest that the low conductivities sometimes observed at shallow depths below the volcanic centers in magmatic–hydrothermal systems may simply reflect elevated temperatures. The strong negative temperature effect on fluid conductivities may offer a possibility for the remote sensing of temperature variations in such systems and may allow distinguishing the effects of magma intrusions from changes in hydrothermal circulation. The generally very high conductivities of HCl–NaCl–H2O fluids at deep crustal pressures (500 MPa–1 GPa) imply that electrical conductors in the deep crust, as in the Altiplano magmatic province and elsewhere, may at least partially be due to hydrothermal activity.

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Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Electrical conductivity of HCl-bearing aqueous fluids to 700 ºC and 1 GPa

Klumbach

Keppler

2020

Contrib Mineral Petrol

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“…(Lisowski et al, ); (2) a low‐velocity zone between about 2 and 3.5 km b.s.l. that may correspond to a shallow magma storage zone (Waite & Moran, ; Wang et al, ); and (3) one or more shallow aquifers beneath the 1980 crater (Bedrosian et al, ; Matoza & Chouet, ; Wynn et al, ).…”

Section: Modeling Surface Deformation and Residual Gravitymentioning

confidence: 99%

“…Another possible contribution to the residual gravity is groundwater accumulation within the volcano during the period spanned by the gravity surveys. There is abundant evidence of an active hydrothermal system at Mount St. Helens, including thermal springs and seeps in several locations (Bergfeld et al, ), and seismic and geophysical data indicative of one or more shallow aquifers (Bedrosian et al, ; Matoza & Chouet, ; Wynn et al, ). Potential hosts for the aquifer(s) include unconsolidated volcanic products within a few hundred meters below the 1980 landslide surface in the crater and fragmental material that has accumulated on the crater floor since 1980.…”

Section: Modeling Surface Deformation and Residual Gravitymentioning

confidence: 99%

Mass Addition at Mount St. Helens, Washington, Inferred From Repeated Gravity Surveys

et al. 2018

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Relative gravity measurements were made at 12 sites on Mount St. Helens and 4 sites far afield during the summers of 2010, 2012, 2014, and 2016. Positive residual gravity changes of 0.05–0.06 ± 0.01 mGal from 2010 to 2016—a sign of mass addition—remain at proximal sites after accounting for the effects of changes in Crater Glacier shape and mass. Modeling of the 2010–2016 monitoring data indicates mass addition in the volcano magma reservoir, the volcano conduit, and/or the shallow hydrothermal aquifer. Magma intrusion in the volcano's known reservoir is suggested by the joint inversion of GPS and gravity data (d = 5800 ± 710 m below sea level, ΔVm = 49.8 ± 8.6 × 106m3, ρ = 1930 ± 300 kg/m3); the modeled depth and location are consistent with that of the reservoir that fed the 2004–2008 eruption, and its mass change can explain up to 19% of the residual gravity. The other two potential sources—the conduit and shallow aquifer—are not well constrained. Magma addition along the volcano conduit can explain up to 62% of the residual gravity (ΔVm ≅ 31 × 106m3, ρm ≅ 2, 300 kg/m3). However, such an intrusion should have produced a measurable surface deformation, which is not observed in the GPS time series. Changes in the level of the volcano's shallow hydrothermal system (ρw = 1, 000 kg/m3) can explain 17% (ΔVrecharge ≅ 9 × 106m3) to 61% (ΔVrecharge ≅ 30 × 106m3) of the residual gravity. It would therefore seem that the bulk of the mass change measured at Mount St. Helens during 2010–2016 was caused by shallow accumulation of water beneath the floor of the crater.

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“…Aqueous fluids in crust and mantle are usually electrically conductive, as they contain dissolved salts that are partially dissociated into ions. Electrical conductivities obtained from magnetotelluric surveys of the mantle wedge (e.g., Pommier, ; Worzewski et al, ), of the deep crust (e.g., Chen et al, ; Gaillard et al, ), or in the crust below active volcanoes (e.g., Hoffmann‐Rothe et al, , Wynn et al, ) could therefore constrain the nature and abundance of fluids present in these systems. However, the interpretation of such magnetotelluric data is presently severely hampered by insufficient fluid conductivity data at high pressures and temperatures.…”

Section: Introductionmentioning

confidence: 99%

Electrical Conductivity of NaCl‐Bearing Aqueous Fluids to 900 °C and 5 GPa

Guo

Keppler

2019

JGR Solid Earth

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The electrical conductivity of aqueous fluids containing 0.01, 0.1, and 1 M NaCl was measured in a piston‐cylinder apparatus up to 900 °C and 5 GPa. The conductivity generally increases with NaCl concentration, while the pressure and temperature effects are more complex. At 1–2 GPa, the effect of temperature on conductivity is small, while at higher pressures, conductivity increases with temperature. Pressure also enhances conductivity, but only above 300–400 °C. This effect may be due to enhanced ion dissociation in response to an increasing dielectric constant. However, at lower temperatures, conductivity decreases with pressure, probably due to an increase in fluid viscosity. The measured conductivities of NaCl‐H2O fluids up to 900 °C and 5 GPa are reproduced (R2 = 0.953) by a numerical model with log σ = −0.919 − 872.5/T + 7.61 log ρ + 0.852 log c + log Λ0, where σ is the conductivity in S/m, T is temperature in K, c is NaCl concentration in wt%, ρ is the density of pure water (in g/cm3) at given pressure and temperature, and Λ0 is the molar conductivity of NaCl in water at infinite dilution (in S·cm2·mol−1), Λ0 = 1,573 − 1,212 ρ + 537,062/T – 208,122,721/T2. We use our data to model the elevated electrical conductivity in the mantle wedge above subducted slabs. We find that due to the strong conductivity enhancement, in most cases less than one volume percent of aqueous fluid with moderate salinity is sufficient to explain the observed conductivity anomalies.

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Where is the Hot Rock and Where is the Ground Water – Using CSAMT to Map Beneath and Around Mount St. Helens

Cited by 25 publications

References 22 publications

Electrical conductivity of HCl-bearing aqueous fluids to 700 ºC and 1 GPa

Electrical conductivity of HCl-bearing aqueous fluids to 700 ºC and 1 GPa

Mass Addition at Mount St. Helens, Washington, Inferred From Repeated Gravity Surveys

Electrical Conductivity of NaCl‐Bearing Aqueous Fluids to 900 °C and 5 GPa

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