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

Abstract

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.

Does a Shallow Magma Reservoir Exist in the Wudalianchi Volcanic Field? Constraints From Magnetotelluric Imaging

“…In some volcanic areas, magma reservoirs have been observed to have lateral offsets when extending to depth, such that their surface projection is not coincident with the location of the volcano (Bedrosian et al., 2018; Cordell et al., 2018; Hill et al., 2009, 2022; Lerner et al., 2020; Triahadini et al., 2023); however, most of these magma reservoirs are found in the lower crust or mantle (Kelbert et al., 2012; H. Zhang et al., 2016), or they coexist with another shallow magma reservoir (or multiple reservoirs) that directly supplies magma to an overlying volcano (Díaz et al., 2020). Indeed, magma reservoirs in the upper crust are typically located beneath the volcano (Comeau et al., 2015; Cordell et al., 2019; Hata et al., 2016; Hill et al., 2015, 2020). Therefore, due to the lateral offsets of the magma reservoirs and the absence of conduits connecting these reservoirs to the volcanoes, we consider it highly unlikely that magma is migrating along plunging structure C1 to erupt at Laoheishan and Huoshaoshan volcanoes.…”

“…Many MT studies in volcanic areas suggest that low‐resistivity bodies in the crust are usually associated with crustal magma, fluids, and/or sulfide mineralization (Cheng et al., 2019; Cordell, Hill, et al., 2022, Cordell, Naif, et al., 2022; Heise et al., 2016; Hill et al., 2020; Liu et al., 2019; MacQueen et al., 2021; H. Zhang et al., 2016). Given that sulfide mineralization typically correspond to high‐density anomalies (MacQueen et al., 2021), it is intriguing to note that, based on the results from gravimetric surveying and inversion, the material underlying the Weishan Volcano (at the same position as C1) exhibits a density lower than that of the surrounding rock (S. Zhang et al., 2018).…”

“…Many MT studies in volcanic areas suggest that low-resistivity bodies in the crust are usually associated with crustal magma, fluids, and/or sulfide mineralization (Cheng et al, 2019;Cordell, Hill, et al, 2022, Cordell, Naif, et al, 2022Heise et al, 2016;Hill et al, 2020;Liu et al, 2019;MacQueen et al, 2021;H. Zhang et al, 2016).…”

Magma Chamber Detected Beneath an Arc Volcano With Full‐Waveform Inversion of Active‐Source Seismic Data

“…However, this shape may not be well constrained, as indicated by the relatively large uncertainty associated with this part of the model (Figure S4 in Supporting Information ) and the smearing at the top of the recovered synthetic anomaly (Figure S5 in Supporting Information ). If we were to treat the mushroom‐like shape of the anomaly as a real feature, its broad top may represent a lens of brine (Hill et al., 2020) separated from magma ponding below the high‐temperature hydrothermal system (Hübscher et al., 2015; Rizzo et al., 2016; Sigurdsson et al., 2006). In turn, the narrow base may reflect the predominant path of magma supplied through a rheologically strong layer (Schmid et al., 2022) that overlies a yet‐to‐be‐imaged deeper mush zone.…”

Multi-scale imaging of 3-D electrical conductivity structure under the contiguous US constrains lateral variations in the upper mantle water content

“…Magnetotellurics (MT) is a method that uses natural time variations of electromagnetic (EM) field to probe the electrical conductivity structure from surface down to depths of several hundreds kilometers (Rikitake, 1948;Tikhonov, 1950;Cagniard, 1953). Over the past decades, the MT method has been widely applied to image shallow volcanic and geothermal systems (e.g., Heise et al, 2007;Hill et al, 2009;Bertrand et al, 2012;Munoz, 2014;Peacock et al, 2016;Samrock et al, 2018;Hill et al, 2020) as well as crustal and lithospheric structures at regional scales (Khoza et al, 2013;Tietze and Ritter, 2013;Nieuwenhuis et al, 2014;Cherevatova et al, 2015;Robertson et al, 2017;Xu et al, 2019;Murphy and Egbert, 2017, among others).…”