Search

The presence of mafic enclaves and banded pumice reveals key physical processes associated with volcanic eruptions. Here, through the textural and geochemical analyses of the 3550 B.P. Waimihia deposits in Taupō, New Zealand, we demonstrate how disequilibrium crystallization controls the way magmas mix. Andesitic enclaves in pyroclastic deposits from this predominantly rhyolitic eruption consist of microlites that crystallized rapidly during mafic injection into rhyolitic host magma. The variation of microlite textures depends on enclave size, implying that mafic enclaves crystallized as discrete blobs within a host rhyolitic magma. However, gray pumice and dark bands in banded pumice are characterized by a lack of or less plagioclase microlites that should be present if equilibrium crystallization occurred. Our textural and chemical data suggest that the lack of plagioclase in gray pumice and dark bands resulted from the nucleation delay arising from the mixing with rhyolitic magma. After mafic magma broke up in a magma chamber as discrete mafic blobs, the plagioclase-free rim of the blobs was disaggregated by shear flow. The eroded mafic blobs form a hybrid magma by mixing with rhyolitic magma, which further delays the plagioclase nucleation. This hybrid magma eventually erupted as gray pumice or banded pumice, depending on the intensity of magma mingling in the conduit. We use a plagioclase nucleation delay model to calculate residence times of hours to tens of hours prior to eruption. Our mixing model with nucleation delay enables small volumes of mafic magma to mix with large amounts of silicic magma. [ABSTRACT FROM AUTHOR]

The geomechanical characterization of volcanic material has important implications for geothermal and mineral exploration, engineering design, geophysical signals of volcano unrest, and models of instability and mass flows. Chemical weathering and hydrothermal systems can alter the host rock, leading to changes in mechanical behavior and failure mode. Here, we compare the physical and mechanical properties of lava, autoclastic breccia, and pyroclastic (scoria) rocks from Mount Ruapehu volcano (Ruapehu) in New Zealand to mineralogical composition determined via infrared spectroscopy and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). We use correlation matrices, principal component analysis, and parametric analysis to determine which parameters can be used to predict physical and mechanical properties and form the basis for transfer functions. Laboratory-based spectroscopy shows that the samples contain absorption features indicative of Al- and Mg-rich hydrous phyllosilicates (e.g., kaolinite, halloysite, montmorillonite), Fe- oxides (e.g., goethite), and sulfates attributed to surface weathering, supergene, and steam-heated alteration. We find that porosity and primary lithology are the predominant control on physical and mechanical properties, followed by the pervasiveness of weathering/alteration, and then mineralogical composition. Several properties, such as porosity, uniaxial compressive strength, P-wave seismic velocity, density, and Young's modulus, show strong correlations with other properties, indicating the potential for transfer functions between these properties. Hydrothermally altered rocks near the vent complex (up to ~ 400 m depth beneath the crater lake) with high-intensity hydrothermal alteration do not follow typical physical and mechanical property trends due to high clay content, low permeability, and low strength. The presence of these rocks within the edifice at Ruapehu implies local barriers to fluid flow and subsequent pore pressure variations. Additionally, they may have less than half the strength than would be dictated by typical porosity-strength trends for surface rocks, increasing the likelihood of structural failure. Trends in the pervasiveness of weathering with physical and mechanical properties, along with shifts in the position of spectral absorption peaks as hydrothermal/weathering alteration increases, suggest that it may be possible to extrapolate properties from imaging spectroscopy. [ABSTRACT FROM AUTHOR]

This paper considers the non-isothermal flow of a viscoplastic fluid on a horizontal or an inclined surface with a flat, a step-up and a step-down topography. A particular application of interest is the spread of a fixed mass—a block—of material under its own weight. The rheology of the fluid is described by the Bingham model which includes the effect of yield stress, i.e. a threshold stress which must be exceeded before flow can occur. Both the plastic viscosity and the yield stress are modelled with temperature-dependent parameters. The flow is described by a reduced model with a thin-film equation for the height of the block and a depth-averaged energy conservation equation for the heat transfer. Results show that for large values of the yield stress, only the outer fraction of the fluid spreads outward, the inner fraction remaining unyielded, hence the block only partially slumps. Conversely, for small values of the yield stress, the entire block of fluid becomes yielded and therefore slumps. We present an analysis which predicts the critical value of the yield stress for which partial slump occurs and how it depends on temperature. [ABSTRACT FROM AUTHOR]

Laterally directed explosive eruptions are responsible for multiple fatalities over the past decade and are an increasingly important volcanology problem. To understand the energy dynamics for these events, we collected field-scale explosion data from nine acoustic sensors surrounding a tiltable cannon as part of an exploratory experimental design. For each cannon discharge, the blast direction was varied systematically at 0°, 12°, and 24° from vertical, capturing acoustic wavefield directivity related to the tilt angle. While each event was similar in energy discharge potential, the resulting acoustic signal features were variable event-to-event, producing non-repetitious waveforms and spectra. Systematic features were observed in a subset of individual events for vertical and lateral discharges. For vertical discharges, the acoustic energy had a uniform radiation pattern. The lateral discharges showed an asymmetric radiation pattern with higher frequencies in the direction of the blast and depletion of those frequencies behind the cannon. Results suggest that, in natural volcanic systems, near-field blast directionality may be elucidated from acoustic sensors in absence of visual data, with implications for volcano monitoring and hazard assessment. [ABSTRACT FROM AUTHOR]

Cycles of stress build-up and release are inherent to tectonically active planets. Such stress oscillations impart strain and damage, prompting mechanically loaded rocks and materials to fail. Here, we investigate, under uniaxial conditions, damage accumulation and weakening caused by time-dependent creep (at 60, 65, and 70% of the rocks' expected failure stress) and repeating stress oscillations (of ± 2.5, 5.0 or 7.5% of the creep load), simulating earthquakes at a shaking frequency of ~ 1.3 Hz in volcanic rocks. The results show that stress oscillations impart more damage than constant loads, occasionally prompting sample failure. The magnitudes of the creep stresses and stress oscillations correlate with the mechanical responses of our porphyritic andesites, implicating progressive microcracking as the cause of permanent inelastic strain. Microstructural investigation reveals longer fractures and higher fracture density in the post-experimental rock. We deconvolve the inelastic strain signal caused by creep deformation to quantify the amount of damage imparted by each individual oscillation event, showing that the magnitude of strain is generally largest with the first few oscillations; in instances where pre-existing damage and/or the oscillations' amplitude favour the coalescence of micro-cracks towards system scale failure, the strain signal recorded shows a sharp increase as the number of oscillations increases, regardless of the creep condition. We conclude that repetitive stress oscillations during earthquakes can amplify the amount of damage in otherwise mechanically loaded materials, thus accentuating their weakening, a process that may affect natural or engineered structures. We specifically discuss volcanic scenarios without wholesale failure, where stress oscillations may generate damage, which could, for example, alter pore fluid pathways, modify stress distribution and affect future vulnerability to rupture and associated hazards. [ABSTRACT FROM AUTHOR]

Over the past 20 years, our understanding of volcanic eruption impacts on the built environment has transformed from being primarily observational with small datasets to one grounded in field investigations, laboratory experiments, and quantitative modeling, with an emphasis on stakeholder collaboration and co-creation. Here, we summarize key advances and knowledge gaps of impacts across volcanic hazards and built environment types from the past 20 + years. Studies have concentrated on impacts from tephra fall (ash) and to buildings, with less examination of other hazards' impacts to critical infrastructure. As we look to the next decade, we speculate on likely research directions, including the increasing role of new technologies, higher resolution modeling, transdisciplinary collaborations, and evidence-based mitigative solutions. [ABSTRACT FROM AUTHOR]

A new episode of unrest and phreatic/phreatomagmatic/magmatic eruptions occurred at Ambae volcano, Vanuatu, in 2017–2018. We installed a multi-station seismo-acoustic network consisting of seven 3-component broadband seismic stations and four 3-element (26–62 m maximum inter-element separation) infrasound arrays during the last phase of the 2018 eruption episode, capturing at least six reported major explosions towards the end of the eruption episode. The observed volcanic seismic signals are generally in the passband 0.5–10 Hz during the eruptive activity, but the corresponding acoustic signals have relatively low frequencies (< 1 Hz). Apparent very-long-period (< 0.2 Hz) seismic signals are also observed during the eruptive episode, but we show that they are generated as ground-coupled airwaves and propagate with atmospheric acoustic velocity. We observe strongly coherent infrasound waves at all acoustic arrays during the eruptions. Using waveform similarity of the acoustic signals, we detect previously unreported volcanic explosions at the summit vent region based on constant-celerity reverse-time-migration (RTM) analysis. The detected acoustic bursts are temporally related to shallow seismic volcanic tremor (frequency content of 5–10 Hz), which we characterise using a simplified amplitude ratio method at a seismic station pair with different distances from the vent. The amplitude ratio increased at the onset of large explosions and then decreased, which is interpreted as the seismic source ascent and descent. The ratio change is potentially useful to recognise volcanic unrest using only two seismic stations quickly. This study reiterates the value of joint seismo-acoustic data for improving interpretation of volcanic activity and reducing ambiguity in geophysical monitoring. [ABSTRACT FROM AUTHOR]

A Correction to this paper has been published: https://doi.org/10.1007/s00445-021-01441-8 [ABSTRACT FROM AUTHOR]

It is generally accepted that tectonic earthquakes may trigger volcanic activity, although the underlying mechanisms are poorly constrained. Here, we review current knowledge, and introduce a novel framework to help characterize earthquake-triggering processes. This framework outlines three parameters observable at volcanoes, namely magma viscosity, open- or closed-system degassing and the presence or absence of an active hydrothermal system. Our classification illustrates that most types of volcanoes may be seismically-triggered, though require different combinations of volcanic and seismic conditions, and triggering is unlikely unless the system is primed for eruption. Seismically-triggered unrest is more common, and particularly associated with hydrothermal systems. This review dives deep into how earthquakes affect volcanoes, specifically into the relation between tectonic seismic activity and subsequent eruptions. Activity may increase in any volcanic setting in the 2–5 years following an earthquake, and especially at volcanic centres featuring vigorous hydrothermal activity. [ABSTRACT FROM AUTHOR]

Purpose: The present study identified the physiological and performance characteristics that are deterministic during a maximal 1500-m time trial and in paced 1500-m time trials, with an all-out last lap.Methods: Thirty-two trained middle-distance runners (n = 21 male, VO2peak: 72.1 ± 3.2; n = 11, female, VO2peak: 61.2 ± 3.7 mL kg-1 min-1) completed a 1500-m time trial in the fastest time possible (1500FAST) as well as a 1500MOD and 1500SLOW trial whereby mean speed was reduced during the 0-1100 m by 5% and 10%, respectively. Anaerobic speed reserve (ASR), running economy (RE), the velocity corresponding with VO2peak (VVO2peak), maximal sprint speed (MSS) and maximal accumulated oxygen deficit (MAOD) were determined during additional testing. Carnosine content was quantified by proton magnetic resonance spectroscopy in the gastrocnemius and expressed as a Z-score to estimate muscle fibre typology.Results: 1500FAST time was best explained by RE and VVO2peak in female runners (adjusted r2 = 0.80, P < 0.001), in addition to the 0-1100-m speed relative to VVO2peak in male runners (adjusted r2 = 0.72, P < 0.001). Runners with a higher gastrocnemius carnosine Z-score (i.e., higher estimated percentage of type II fibres) and greater MAOD, reduced their last lap time to a greater extent in the paced 1500-m trials. Neither ASR nor MSS was associated with last lap time in the paced trials.Conclusion: These findings suggest that VVO2 peak and RE are key determinants of 1500-m running performance with a sustained pace from the start, while a higher carnosine Z-score and MAOD are more important for last lap speed in tactical 1500-m races. [ABSTRACT FROM AUTHOR]

We have observed very long period earthquakes (VLPs) over the period 2007 to the end of 2019 at Whakaari/White Island volcano, New Zealand. The earthquakes exhibit similitude between waveforms which suggests repeating source locations and processes. VLPs recorded at two permanent stations were detected using waveform semblance and were then classified into two main families (F1 and F2) using a clustering analysis. The two families are characterized by 'mirror image' reverse waveform polarity suggesting that they are genetically related, but occur during different evolutionary phases of volcanic activity. F1 events occurred throughout the observation period, while F2 events mainly occurred as swarms that mark the onset of volcanic unrest. A detailed cluster analysis reveals possible sub-families implying slight temporal evolutions within a family. Our results add to our understanding of the volcanic magma–hydrothermal system at Whakaari/White Island indicating that relatively stable VLP sources may be exploited to improve monitoring for future unrest. [ABSTRACT FROM AUTHOR]

As populations around volcanoes grow, the potential for society to be impacted by lava flows is increasing. While lava flows are known to ignite, bulldoze and/or bury structures, little is known about potential impacts to buried infrastructure. We measure temperature profiles below molten rock to constrain a heat transfer model. Thermomagnetic and palaeomagnetic measurements on soil samples from beneath a 2014 Hawaiian lava flow are then used to verify the model. Finally, we illustrate the model's utility in lava flow hazard assessments by modelling a hypothetical lava flow active for 4 weeks in Auckland (New Zealand). The modelling predicts the upper 1.7 m of dry soil would exceed 100 °C after 1 week, and the upper 3.8 m of soil would exceed 100 °C after 4 weeks. Determining the depth profile of substrate heating has important implications for planning and preparedness (e.g. siting buried infrastructure), volcanic impact and risk assessments, and decision-making before and during lava flow crises (e.g. mitigation measures to be employed). [ABSTRACT FROM AUTHOR]

Field evidence from a basaltic-andesite dyke preserved in the eroded wall of a scoria cone at Red Crater, Tongariro volcano, New Zealand, records a history of up-conduit magma flow during a Strombolian eruption, subsequent drain-back and final cessation of flow. The dyke intrudes pre-Strombolian andesite lavas, and the overlying proximal basaltic-andesite scoria deposits associated with contemporaneous lavas, which are, in turn overlain by laminated lapilli-tuff and large blocks. Textural and kinematic evidence of ductile shear recorded in basaltic andesite at the dyke margins records magma deformation imposed by bypassing movement of magma up the centre of the conduit during the eruption, whereas the basaltic andesite occupying the central part of the lowermost exposures of the dyke preserves ductile flow-folds with the opposite (down-flow) shear sense. The evidence indicates that the downward magma flow followed the eruption, and this draining left the central part of the dyke empty (unfilled) at uppermost levels. We discuss the kinematic constraints in the context of the criteria for up-flow of mafic magma and present the factors most likely to result in a final drain-back event. With reference to experimental and numerical work, we propose a draining model for the end of this eruption, and that magmatic drain-back may feature commonly during closing stages of Strombolian eruptions at mafic volcanoes. Drain-back which leaves large cavities in a volcanic edifice could result in hazardous structural instabilities. [ABSTRACT FROM AUTHOR]

A key question in volcanology is the driving mechanisms of resurgence at active, recently active, and ancient calderas. Valles caldera in New Mexico and Lake City caldera in Colorado are well-studied resurgent structures which provide three crucial clues for understanding the resurgence process. (1) Within the limits of Ar/Ar dating techniques, resurgence and hydrothermal alteration at both calderas occurred very quickly after the caldera-forming eruptions (tens of thousands of years or less). (2) Immediately before and during resurgence, dacite magma was intruded and/or erupted into each system; this magma is chemically distinct from rhyolite magma which was resident in each system. (3) At least 1 km of structural uplift occurred along regional and subsidence faults which were closely associated with shallow intrusions or lava domes of dacite magma. These observations demonstrate that resurgence at these two volcanoes is temporally linked to caldera subsidence, with the upward migration of dacite magma as the driver of resurgence. Recharge of dacite magma occurs as a response to loss of lithostatic load during the caldera-forming eruption. Flow of dacite into the shallow magmatic system is facilitated by regional fault systems which provide pathways for magma ascent. Once the dacite enters the system, it is able to heat, remobilize, and mingle with residual crystal-rich rhyolite remaining in the shallow magma chamber. Dacite and remobilized rhyolite rise buoyantly to form laccoliths by lifting the chamber roof and producing surface resurgent uplift. The resurgent deformation caused by magma ascent fractures the chamber roof, increasing its structural permeability and allowing both rhyolite and dacite magmas to intrude and/or erupt together. This sequence of events also promotes the development of magmatic-hydrothermal systems and ore deposits. Injection of dacite magma into the shallow rhyolite magma chamber provides a source of heat and magmatic volatiles, while resurgent deformation and fracturing increase the permeability of the system. These changes allow magmatic volatiles to rise and meteoric fluids to percolate downward, favouring the development of hydrothermal convection cells which are driven by hot magma. The end result is a vigorous hydrothermal system which is driven by magma recharge. [ABSTRACT FROM AUTHOR]

Alemtuzumab (MabCampath™) can purge both B- and T-cells in a variety of clinical situations, as seen in the treatment of autoimmune disorders and of lymphoid malignancies such as B-cell chronic lymphocytic leukemia (B-CLL). One of the characteristics of advanced B-CLL is an increased susceptibility to infection, which may improve in patients whose disease responds to alemtuzumab, particularly when immune reconstitution by non-malignant stem cells is successful. However, at initiation of treatment, patients with advanced disease are likely to have poor immune function, and need careful management during and after treatment. Here, we present results showing the nature of immune reconstitution after alemtuzumab and the ways in which alemtuzumab may affect white cell counts during and after treatment. The management of B-CLL patients is discussed both in the context of minimizing acute “first-dose” events and with reference to the health risks already existing in this patient population. With protocols in place for dose escalation, for dose postponement in the event of cytopenia, and for anti-infective prophylaxis, alemtuzumab can be used effectively and safely in high-risk B-CLL patients. [ABSTRACT FROM AUTHOR]

Lava flows can cause substantial physical damage to elements of the built environment. Often, lava flow impacts are assumed to be binary, i.e. cause complete damage if the lava flow and asset are in contact, or no damage if there is no direct contact. According to this paradigm, buried infrastructure would not be expected to sustain damage if a lava flow traverses the ground above. However, infrastructure managers ("stakeholders") have expressed concern about potential lava flow damage to such assets. We present a workflow to assess the thermal hazard posed by lava flows to buried infrastructure. This workflow can be applied in a pre-defined scenario. The first step in this workflow is to select an appropriate lava flow model(s) and simulate the lava flow's dimensions, or to measure an in situ lava flow's dimensions. Next, stakeholders and the modellers collaborate to identify where the lava flow traverses buried network(s) of interest as well as the thermal operating conditions of these networks. Alternatively, instead of direct collaboration, this step could be done by overlaying the flow's areal footprint on local infrastructure maps, and finding standard and maximum thermal operating conditions in the literature. After, the temperature of the lava flow at the intersection point(s) is modelled or extracted from the results of the first step. Fourth, the lava flow-substrate heat transfer is calculated. Finally, the heat transfer results are simplified based on the pre-identified thermal operating conditions. We illustrate how this workflow can be applied in an Auckland Volcanic Field (New Zealand) case study. Our case study demonstrates considerable heat is transferred from the hypothetical lava flow into the ground and that maximum operating temperatures for electric cables are exceeded within 1 week of the lava flow front's arrival at the location of interest. An exceedance of maximum operating temperatures suggests that lava flows could cause thermal damage to buried infrastructure, although mitigation measures may be possible. [ABSTRACT FROM AUTHOR]

Buried volcanoes occur in great numbers within sedimentary basins globally. Knowledge of ancient buried volcanic systems has improved significantly over the past two decades. The in-depth understanding of these buried systems was mainly possible due to increasing availability of high-quality seismic reflection and subsurface borehole data. This paper examines a cluster of Miocene volcanoes now buried by ca. 1000 m of sedimentary strata in the Canterbury Basin, New Zealand. These volcanoes were imaged by 2D seismic lines and perforated by the Resolution-1 borehole. We refer to this group of volcanoes and related intrusive bodies as the Maahunui Volcanic Field (MVF). Here, we present detailed petrographic and seismic reflection interpretation of some representative volcanoes of the MVF, and of the strata that enclose them, to constrain the environments in which intrusions and eruptions occurred. Intrusive rocks penetrated by the Resolution-1 comprise a monzogabbro body with a saucer-shape geometry emplaced in organic-rich sedimentary layers. The monzogabbro contains miarolitic cavities and ophitic textures which, together with decompaction of its overburdened sedimentary strata, suggest an emplacement depth around 950 m below the paleo-seafloor. Seismic lines show an array of faults at the tips of the saucer-shaped monzogabbro. These faults are connected with the root of some volcanoes and may have formed feeder systems for eruptions and hydrothermal fluids onto the Miocene paleo-seafloor. Volcaniclastic rocks comprise abundant glassy shards, relics of bubble walls, spheroidal fragments enveloped in a palagonite film, broken phenocrysts, and lithics. These volcaniclastic rocks are interbedded with lower bathyal siltstones, indicating that eruptions near the location of the Resolution-1 occurred in a deep-submarine environment (1000–1500 m). Integration of petrographic, geochemical, and seismic reflection interpretation suggest that the volcaniclastic rocks have a genetic relationship with the saucer-shaped monzogabbro, which may have served as a shallow stationary magma chamber for some volcanoes in the MVF. The available data indicate processes of intense material fragmentation and particle dispersion, consistent with phreatomagmatic eruptions, although globally this eruptive style is rarely interpreted to occur at water depths > 1000 m. The emplacement of intrusions into organic-rich sedimentary rocks could incorporate thermogenic gases into the magmatic system, providing supplementary driving forces to form large deep-water pyroclastic eruptions. [ABSTRACT FROM AUTHOR]

On 27 April 2016, White Island erupted in a multi-pulse, phreatic event that lasted for ~ 40 min. Six, variably sized pulses generated three ballistic ejections and at least one pyroclastic surge out of the inner crater and onto the main crater floor. Deposit mapping of the pyroclastic surge and directed ballistic ejecta, combined with numerical modelling, is used to constrain the volume of the ejecta and the energetics of the eruption. Vent locations and directionality of the eruption are constrained by the ballistic modelling, suggesting that the vent/s were angled towards the east. Using these data, a model is developed that comports with the field and geophysical data. One of the main factors modifying the dispersal of the eruption deposits is the inner crater wall, which is ~ 20 m high. This wall prevents some of the pyroclastic surge and ballistic ejecta from being deposited onto the main crater floor but also promotes significant inflation of the surge, generating a semi-buoyant plume that deposits ash high on the crater walls. While the eruption is small volume, the complexity determined from the deposits provides a case study with which to assess the relatively frequent hazards posed by active volcanoes that host hydrothermal systems. The deposits of this and similar eruptions are readily eroded, and for complete understanding of volcanic hazards, it is necessary to make observations and collect samples soon after these events. [ABSTRACT FROM AUTHOR]

Prehistoric timescales, volcanic hazard assessment, and understanding of volcanogenic climate events rely on accurate dating of prehistoric eruptions. Most late Quaternary eruptions are dated by 14C measurements on material from close to the volcano that may be contaminated by geologic-sourced infinite-age carbon. Here we show that 14C ages for the Taupo (New Zealand) First Millennium eruption are geographically arrayed, with oldest ages closer to the vent. The current eruption wiggle match date of 232 ± 5 years CE is amongst the oldest. We present evidence that the older, vent-proximal 14C ages were biased by magmatic CO2 degassed from groundwater, and that the Taupo eruption occurred decades to two centuries after 232 CE. Our reinterpretation implies that ages for other proximally-dated, unobserved, eruptions may also be too old. Plateauing or declining tree ring cellulose δ13C and Δ14C values near a volcano indicate magmatic influence and may allow forecasting of super-eruptions. [ABSTRACT FROM AUTHOR]