Structure of the Tongariro Volcanic system: Insights from magnetotelluric imaging

Hill, G. J.; Bibby, H. M.; Ogawa, Yasuo; Wallin, Erin L.; Bennie, S. L.; Caldwell, T. G.; Keys, Harry; Bertrand, E. A.; Heise, Wiebke

doi:10.1016/j.epsl.2015.10.003

Cited by 79 publications

(70 citation statements)

References 39 publications

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“…Magnetotellurics (MT) provides glimpse into the subsurface and is a powerful approach to monitor the status of active magma reservoirs [ Utada , ; Hill et al ., ]. In order to interpret the MT results and to relate the inverted electrical resistivity values to petrologic parameters (e.g., melt fraction and H 2 O concentration in the melt), laboratory measurement of electrical conductivity of silicate melts is required.…”

Section: Introductionmentioning

confidence: 99%

Electrical conductivity of hydrous andesitic melts pertinent to subduction zones

Guo

et al. 2017

JGR Solid Earth

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Andesitic magmatism and rocks are widespread at convergent plate boundaries. Electrically conductive bodies beneath subduction zone arc volcanoes, such as the Uturuncu Volcano, Bolivia, may correspond to active reservoirs of H2O‐bearing andesitic magma. Laboratory measurements of electrical conductivity of hydrous andesitic melts are required to constrain the physicochemical conditions of these magma reservoirs in combination with magnetotelluric data. This experimental study investigates electrical conductivity of andesitic melts with 0.01–5.9 wt % of H2O at 1164–1573 K and 0.5–1.0 GPa in a piston cylinder apparatus using sweeping‐frequency impedance spectroscopy. Electrical conductivity of andesitic melt increases with increasing temperature and H2O concentration but decreases with pressure. Across the investigated range of H2O concentration, electrical conductivity varies by 1.2–2.4 log units, indicating stronger influence of H2O for andesitic melt than for rhyolitic and dacitic melts. Using the Nernst‐Einstein equation, the principal charge carrier is inferred to be Na in anhydrous melt but divalent cations in hydrous andesitic melts. The experimental data are regressed into a general electrical conductivity model for andesitic melt accounting for the pressure‐temperature‐H2O dependences altogether. Modeling results show that the conductive layer at >20 km depths beneath the surface of the Uturuncu Volcano could be interpreted by the presence of less than 20 vol % of H2O‐rich andesitic melt (with 6–9 wt % H2O).

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Section: Introductionmentioning

confidence: 99%

Electrical conductivity of hydrous andesitic melts pertinent to subduction zones

Guo

et al. 2017

JGR Solid Earth

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“…Changes in electrical properties or geometry of the magma reservoir (depth~4-10 km) are expected (based on an average of the observed resistivities overlying the magma reservoir) and observed over the period band of~5-50 s (upper three panels of Figure 2). Figure 3 shows the observed difference tensor ellipses at two periods, 5.33 and 28.4 s. The change in phase is highly polarized with the change in orientation direction of the maximum observed preeruption phase tensors (Hill et al, 2015), a result of the extremely large resistivity contrast across the western margin of the reservoir (Figure 3). The observed narrow phase tensor difference ellipses are a result of electrical property variations in the magmatic system aligned with the direction of the original maximum phase.…”

Section: Discussionmentioning

confidence: 96%

Temporal Magnetotellurics Reveals Mechanics of the 2012 Mount Tongariro, NZ, Eruption

Hill

Bibby

Peacock

et al. 2020

Geophysical Research Letters

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Monitoring dynamics of volcanic eruptions with geophysics is challenging. In August and November 2012, two small eruptions from Mount Tongariro provided a unique opportunity to image subsurface changes caused by the eruptions. A detailed magnetotelluric survey of the Tongariro volcanic complex completed prior to the eruption (2008-2010) provides the preeruption structure of the magmatic system. A subset of the initial measurement locations was reoccupied in June 2013. Significant changes were observed in phase tensor data at sites close to the eruptive center. Although subsurface electrical resistivity changed, the geometry of the preeruptive reservoir did not. These subsurface resistivity variations are interpreted as being predominantly caused by interaction of partial melt and the overlying brine layer causing volume reduction of the brine layer through phreatic eruption. The ability to detect significant changes associated with the magma reservoir suggests that magnetotellurics can be a valuable volcano monitoring tool.Plain Language Summary Preeruption and posteruption electromagnetic magnetotelluric measurements are used to determine the variation in subsurface electrical properties resulting from changes in the Tongariro volcanic center magma chamber associated with the 2012 eruptive cycle. The observed electrical property changes are related to the physical eruption properties (e.g., eruptive volume, style, and composition), revealing the state of the magmatic system both prior to and following the eruption. Knowing both the preeruption and posteruption states of the magmatic system and the surface eruptive properties enables reconstruction of the subsurface eruption mechanism. Successful identification of preeruption and posteruptive states of the volcano is evidence for the usefulness of continuous magnetotelluric monitoring of volcanoes to identify variations within magmatic systems that may be indicative of imminent eruption.

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“…A key indicator of magmatic involvement in the unrest included changes in gas composition at fumaroles close to the eruption vent (Christenson et al, ). Curiously, at other hydrothermal features on the edifice (i.e., Ketetahi Hot Springs and Red Crater) no change in gas or liquid composition was detected despite evidence for an extensive, long‐lived (>10 ka) hydrothermal system underlying the entire volcanic center (Hill et al, ; Miller & Williams‐Jones, ; Figure ). The combination of seismic and geochemical changes was interpreted as dyke intrusion overpressuring the hydrothermal system, which led to eruption (Jolly et al, ).…”

Section: Geologic Settingmentioning

confidence: 99%

“…(a) Distribution of self‐potential anomalies at Mount Tongariro with faults, surface thermal features, and other hydrological features labeled. (b, c) Horizontal slices of the conductivity model from Hill et al at 150 and 300 m deep, respectively. Topography from a 15‐m digital elevation model underlies data in a–c.…”

Section: Geologic Settingmentioning

confidence: 99%

Distribution of Vapor and Condensate in a Hydrothermal System: Insights From Self‐Potential Inversion at Mount Tongariro, New Zealand

Miller

Kang

Fournier

et al. 2018

Geophysical Research Letters

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Inversion of self‐potential data for source current density, js, in complex volcanic settings, yields hydrological information without the need for a prior groundwater flow model; js contains information about pH, pore saturation, and permeability, from which we infer the distribution of liquid and vapor phases. To understand the hydrothermal flow dynamics and hydraulic connectivity between surface thermal features at Mount Tongariro volcano, New Zealand, we undertook a reconnaissance scale self‐potential survey and developed an inversion routine for js, constrained by an existing 3‐D conductivity model from magnetotelluric measurements. The 3‐D distribution of js at Mount Tongariro reveals a discontinuous zero js zone interpreted as vapor or residually saturated pore space, surrounded by low to moderate js interpreted as circulating condensate liquid. Bounding faults act as conduits for down flowing groundwater or condensate, as well as barriers for the hydrothermal system. Localized small‐scale circulation associated with individual surface thermal features, rather than a single circulating system, accounts for the lack of widespread anomalous geochemical observations prior to the 2012 Te Maari eruption.

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Structure of the Tongariro Volcanic system: Insights from magnetotelluric imaging

Cited by 79 publications

References 39 publications

Electrical conductivity of hydrous andesitic melts pertinent to subduction zones

Electrical conductivity of hydrous andesitic melts pertinent to subduction zones

Temporal Magnetotellurics Reveals Mechanics of the 2012 Mount Tongariro, NZ, Eruption

Distribution of Vapor and Condensate in a Hydrothermal System: Insights From Self‐Potential Inversion at Mount Tongariro, New Zealand

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