Showing papers by "Colin J. N. Wilson published in 2021"

Taupō: an overview of New Zealand's youngest supervolcano

Abstract: Taupō volcano (New Zealand) is distinguished as the source of Earth's youngest supereruption (∼25.5 ka), with Lake Taupō occupying the resulting caldera. Taupō has also produced eruptions of a wide...

Volcanic Unrest at Taupō Volcano in 2019: Causes, Mechanisms and Implications

Abstract: Taupō volcano, New Zealand, is a large caldera volcano that has been highly active through the Holocene. It most recently erupted ∼1,800 years ago but there have been multiple periods of historic volcanic unrest. We use seismological and geodetic analysis to show that in 2019 Taupō underwent a period of unrest characterized by increased seismic activity through multiple swarms and was accompanied by ground deformation within the caldera. The earthquakes, which include non-double-couple events, serve to outline an aseismic zone beneath the most recent eruptive vents. This aseismic zone is coincident with an inflating source, based on forward modeling of ground deformation data. We infer that this aseismic and deforming region delineates the location of the present day magma reservoir that is ≥250 km3 in volume and has a melt fraction of >20%–30%, inhibiting seismic activity. Our analysis shows that the 2019 unrest at Taupō was volcanic in nature and origin, demonstrating that this is an active and potentially hazardous volcano, and that improving our monitoring and understanding of its behavior is important.

Ruapehu and Tongariro stratovolcanoes: a review of current understanding

Abstract: GNS Science Operations, New Zealand (GNS Science MBIE-funded Strategic Science Investment Fund (SSIF) and its predecessors); Resilience to Nature’s Challenges, New Zealand (National Science Challenge); Ministry for Business Innovation and Employment, New Zealand (MBIE-funded Natural Hazard Research Platform)

No single model for super-sized eruptions and their magma bodies

Abstract: This work has been supported by the Marsden Fund grant VUW0813 (Royal Society of New Zealand to C.J.N.W.), a James Cook Fellowship (Royal Society of New Zealand) to C.J.N.W., and the ECLIPSE Programme, funded by the N.Z. Ministry of Business, Innovation and Employment. G.F.C. is supported by a NERC Standard Grant (NE/T000317/1), M.L.M. is supported by an NSF CAREER grant (EAR 2042662) and S.J.B. acknowledges Marsden Fund grant VUW1627.

The Mesozoic terrane boundary beneath the Taupo Volcanic Zone, New Zealand, and potential controls on geothermal system characteristics

Abstract: The Taupo Volcanic Zone (TVZ) in the central North Island of New Zealand lies across the boundary formed in the late Mesozoic between two major basement regions: the Waipapa and Torlesse composite terranes. However, the precise location of this terrane contact within the TVZ is not well constrained because it is buried beneath Pleistocene volcanic and volcaniclastic sequences locally >3 km thick. Here we report new U-Pb zircon detrital age spectra from basement sandstones and younger Waikora Formation greywacke gravel from five geothermal well core samples and one surface sample. We combine these new data with existing TVZ zircon xenocryst and xenolith age spectra from volcanic host rocks, to correlate these materials with each basement terrane and constrain the likely spatial location and uncertainty of the terrane boundary under the TVZ. Its position with respect to surficial geothermal systems suggests that, at depth, the terrane boundary may have been reactivated by Quaternary extension in the evolving Taupo Rift. Put another way, the past and current position of the Taupo Rift fundamentally may have been controlled by the terrane boundary, which may ultimately be partly responsible for providing enhanced fracture permeability for deep-seated geothermal fluids.

Earthquake analysis suggests dyke intrusion in 2019 near Tarawera volcano, New Zealand

Abstract: Tarawera volcano (New Zealand) is volumetrically dominated by rhyolitic lavas and pyroclastic deposits, but the most recent event in AD 1886 was a basaltic plinian fissure eruption. In March 2019 a swarm of at least 64 earthquakes occurred to the NE of Tarawera volcano, as recorded by the New Zealand Geohazard Monitoring Network (GeoNet). We use seismological analysis to show that this swarm was most likely caused by a dyke intrusion that intruded into the brittle crust between depths of 8–10 km and propagated towards Tarawera volcano for 2 km at a rate of 0.3–0.6 m s$^{-1}$. We infer that this was a dyke of basaltic composition that was stress-guided towards Tarawera volcano by the topographic load of the volcanic edifice. A similar process may have occurred during the 1886 eruption with a dyke sourced from some lateral distance away from the volcano. The 2019 intrusion was not detected by InSAR geodesy and we use synthetic models to show that geodetic monitoring could only detect a >6 m wide dyke at these depths. Improvements to geodetic monitoring, combined with detailed seismological analysis, could better detect future magmatic intrusions in the region and serve to help assess ongoing changes in the magmatic system and the associated possibilities of a volcanic event.

Survival of presolar p-nuclide carriers in the nebula revealed by stepwise leaching of Allende refractory inclusions

Abstract: The 87Rb-87Sr radiochronometer provides key insights into the timing of volatile element depletion in planetary bodies, yet the unknown nucleosynthetic origin of Sr anomalies in Ca-Al–rich inclusions (CAIs, the oldest dated solar system solids) challenges the reliability of resulting chronological interpretations. To identify the nature of these Sr anomalies, we performed step-leaching experiments on nine unmelted CAIs from Allende. In six CAIs, the chemically resistant residues (0.06 to 9.7% total CAI Sr) show extreme positive μ84Sr (up to +80,655) and 87Sr variations that cannot be explained by decay of 87Rb. The extreme 84Sr but more subdued 87Sr anomalies are best explained by the presence of a presolar carrier enriched in the p-nuclide 84Sr. We argue that this unidentified carrier controls the isotopic anomalies in bulk CAIs and outer solar system materials, which reinstates the chronological significance of differences in initial 87Sr/86Sr between CAIs and volatile-depleted inner solar system materials.

Upper limits for phosphine (PH 3 ) in the atmosphere of Mars

Abstract: Phosphine (PH3) is proposed to be a possible biomarker in planetary atmospheres and has been claimed to have been observed in the atmosphere of Venus, sparking interest in the habitability of Venus’s atmosphere. Observations of another biomarker, methane (CH4), have been reported several times in the atmosphere of Mars, hinting at the possibility of a past or present biosphere. The Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter has a spectral range that includes several absorption lines of PH3 with line strengths comparable to previously observed CH4 lines. The signature of PH3 was not observed in the 192 observations made over a full Martian year of observations, and here we report upper limits of 0.1–0.6 ppbv.

A comment on: magma residence and eruption at the Taupō Volcanic Center (Taupō Volcanic Zone, New Zealand)—insights from rhyolite-MELTS geobarometry, diffusion chronometry, and crystal textures, by AS Pamukçu et al., Contrib Mineral Petrol 175:48 (2020)

Abstract: We consider here the validity, accuracy, and precision of rhyolite-MELTS modelling in inferring the pre-eruptive magma storage conditions for the caldera-forming 25.5 ka Oruanui and 232 CE (1.72 ka) Taupō eruptions at Taupō volcano, New Zealand as proposed by Pamukcu et al. (2020: Contrib Mineral Petrol 175: 48). There are four major issues with the modelling as used. First, the model is inappropriately applied for the Taupō event as this magma does not contain phenocrystic quartz. Second, the products of both eruptions, as is typical for virtually all Taupō Volcanic Zone rhyolites, contain plagioclase but lack sanidine, leading to increased model errors beyond those stated. Third, temperatures utilised for modelling crystallisation histories for both magmas are in conflict with independent measures of magmatic temperatures for these rocks. Fourth, glass compositions for each of these eruptions individually fall within analytical uncertainty yet yield model pressures that vary over hundreds of MPa, in part due to contrasting analytical protocols. We conclude that rhyolite-MELTS is too imprecise (errors of ± ~ 100 MPa or more for the methods applied) for quartz + 1 feldspar systems like at Taupō volcano specifically and the Taupō Volcanic Zone in general to be applied with confidence to deriving relative or absolute depths of magma storage.