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The North Island of New Zealand is a region of high volcanic activity, with significant eruptions over the past. Analogous to past events, future volcanic eruptions would produce a considerable volume of ash and granular soils, covering widespread areas and raising concerns for their disposal and storage. Such deposits, primarily airfall tephra, could be potentially used in geotechnical engineering applications such as foundations, roadway embankments and land reclamations. However, before their use as structural fills can be recommended, detailed laboratory investigations of their physical, chemical, compaction, and geotechnical engineering properties (strength, compressibility, collapsibility, liquefaction potential, etc.) must be conducted. Different tephra deposits can be products of different eruptions, so chemical composition analyses can be combined with the physical, compaction, and engineering properties to characterize such deposits. Accordingly, this paper provides useful insights from physical (grain size, specific gravity, and morphology), chemical (elemental and mineralogy using X-ray fluorescence and X-ray diffraction), and compaction tests (maximum dry density, optimum water content, and particle breakage) for eleven selected volcanic tephra samples sourced from the North Island of New Zealand in the Rotorua, Taupo, and Auckland regions. [ABSTRACT FROM AUTHOR]

Whakaari/White Island has been the most active New Zealand volcano in the 21st century, producing small phreatic and phreatomagmatic eruptions, which are hard to predict. The most recent eruption occurred in 2019, tragically claiming the lives of 22 individuals and causing numerous injuries. We employed shear‐wave splitting analyses to investigate variations in anisotropy between 2018 and 2020, during quiescence, unrest, and the eruption. We examined spatial and temporal variations in 3,499 shear‐wave splitting and 2,656 Vp/Vs ratio measurements. Comparing shear‐wave splitting parameters from similar earthquake paths across different times indicates that the observed temporal changes are unlikely to result from variations in earthquake paths through media with spatial variability. Instead, these changes may stem from variations in anisotropy over time, likely caused by changes in crack alignment due to stress or varying fluid content. Plain Language Summary: The most active volcano in New Zealand, known as Whakaari/White Island, has recently experienced numerous minor eruptions, which are hard to predict. The most recent eruption occurred in 2019, tragically claiming the lives of 22 individuals and causing multiple injuries. This study examines the stress field and characteristics of cracks within various parts of the volcano, during the period between 2018 and 2020. We used a method called shear‐wave splitting, which examines the alignment of cracks by measuring the speed of seismic waves in different orientations, and another method that measures the ratio of the speed of two different types of waves traveling through the medium (Vp/Vs). Our analysis revealed that both shear‐wave splitting and Vp/Vs changed over time in response to the variations in magmatic activity. This suggests that crack alignment, content, or numbers change in response to the stresses induced by magmatic activity at various depths within the volcano over time. Key Points: Background fast orientations were concentrated parallel to the crater wall at both measurement stationsSeismic waves that follow similar paths to the stations result in different fast orientations pre‐ and post‐eruptionVp/Vs ratio can provide valuable insights into the nature and evolution of seismic anisotropy in the Earth's interior [ABSTRACT FROM AUTHOR]

Tsunamis generated by the Hunga Tonga–Hunga Ha'apai volcanic eruption on January 15, 2022 were recorded on ocean bottom pressure and tide gauges around the Pacific Ocean, earlier than the expected arrival times calculated by tsunami propagation speed. Atmospheric waves from the eruption were also recorded globally with propagation speeds of ~ 310 m/s (Lamb wave) and 200–250 m/s (Pekeris wave). Previous studies have suggested that these propagating atmospheric waves caused at least the initial part of the observed tsunami. We simulated the tsunamis generated by the propagation of the Lamb and Pekeris waves by adding concentric atmospheric pressure changes. The concentric sources are parameterized by their propagation speeds, initial atmospheric wave amplitudes that decay with the distance, and a rise time. For the Lamb wave, inversions of the observed tsunami waveforms at 14 U.S. and nine New Zealand DART stations indicate the start of the positive rise at 4:16 UTC, the peak amplitude of 383 hPa, and the propagation speed of 310 m/s, assuming a rise time of 10 min. The later phases of the observed tsunami waveforms can be better reproduced by adding another propagating concentric wave (Pekeris wave) with a negative amplitude (− 50 hPa) and propagation speeds of 200–250 m/s. The DART records around the Pacific indicate that the Pekeris wave speed is faster toward the northwest and slightly slower toward the northeast. The synthetic waveforms roughly reproduced the far-field tsunami waveforms recorded at tide gauge stations, including the later phases, suggesting that the large amplitude in the later phase may be due to the coupling of the Pekeris wave and the tsunami, as well as resonance around tide gauge stations. [ABSTRACT FROM AUTHOR]

Several studies suggest that large earthquakes (M > 7.0) can act as external triggers of volcanic unrest, and even eruption. This triggering is attributed to either ground shaking (dynamic stresses) or to permanent ground deformation (associated with static stress changes). However, large earthquakes are rare and testing triggering hypotheses has proven difficult. We use geodetic data to show that the 13 November 2016 Kaikōura earthquake (Mw 7.8) triggered local deformation of up to 11 mm at Taupō volcano, 500 km away, which lasted for approximately twelve days. Using elastic geodetic models, we infer that the observed deformation was caused by either aseismic fault slip or a dike intrusion. We then use strong motion data from the surrounding area to show that the Kaikōura earthquake caused maximum dynamic stress changes in the range of 0.15–0.9 MPa in the vicinity of Taupō volcano and conclude that these dynamic stress changes triggered local faulting or dike activity and the associated deformation at Taupō volcano. Plain Language Summary: It has often been proposed that large earthquakes can trigger volcanic eruptions. However, large earthquakes are rare and testing these triggering hypotheses is therefore difficult. We show that the 13 November 2016 Kaikōura earthquake triggered local ground movement at Taupō volcano, 500 km away, which lasted for approximately two weeks. We show that the observed ground movement was caused by either slow movement on a fault or by the movement of magma at depth. We then use seismology data from the surrounding area to show that the Kaikōura earthquake caused large pressure changes in the vicinity of Taupō volcano. We conclude that the ground shaking from the earthquake caused local faulting or magmatic activity and the associated ground movement at Taupō volcano. Key Points: The Mw7.8 Kaikōura earthquake was followed by local deformation at Taupō volcano, c. 500 km awayThe deformation observed is consistent with either a dike intrusion or aseismic slip on a faultDynamic stress changes in the range of 0.15–0.9 MPa caused by seismic waves from the Kaikōura earthquake triggered this response at Taupō [ABSTRACT FROM AUTHOR]

Ahi Tupua, the central section of the Taupō Volcanic Zone in the central North Island of New Zealand, encompasses Taupō and Ōkataina calderas and has been the most frequently active and productive silicic magma system worldwide during the Quaternary. The entire Taupō Volcanic Zone is underlain by the Hikurangi Subduction Zone where a Large Igneous Province, the Hikurangi Plateau, is being subducted, but Ahi Tupua exhibits much higher rates of magma output than either the northern or the southern sections. Trace element signatures of Ahi Tupua eruptive products suggest that both decompression melting and flux melting play a role in this rifted arc setting, with fluid flux signatures being more prevalent in regions of active caldera volcanism. Intermediate‐depth (50–300 km) earthquakes provide a means of studying faulting and fluid flow processes within and around the subducting slab beneath Ahi Tupua. Using data from the national seismic network and a 13‐station temporary network ("ECLIPSE"), we repick and relocate 397 intermediate‐depth earthquakes of magnitudes M2.5+ that occurred in a 29‐month interval, and compute focal mechanisms for a subset of 47 earthquakes. We observe some seismicity that may be within the mantle wedge but most of the relocated earthquakes occur within the crust and uppermost mantle of the subducted slab and exhibit a weak transition from predominantly normal‐faulting in the slab crust to predominantly reverse‐faulting in the slab mantle. No double seismic zone is observed beneath Ahi Tupua. These observations are consistent with dehydration of the slab and flow of slab‐derived fluids along existing faults into the mantle wedge, that drives flux melting and accounts for the distinctive geochemical signatures and voluminous output of Ahi Tupua calderas. Plain Language Summary: Ahi Tupua is a volcanic region in the North Island of New Zealand that is the most active silicic volcanic system on Earth. It includes the active caldera volcanoes Taupō and Ōkataina. This volcanic region lies above the Hikurangi Subduction Zone, and studies of past eruptions suggest that Ahi Tupua's high rate of activity is driven by fluids released deep in the subduction zone. In this study, we use seismic data from across the entire North Island to investigate earthquakes occurring at depths of 50–300 km within the Hikurangi Subduction Zone. We show that these earthquakes suggest that the subducting oceanic crust is releasing a substantial amount of water into the overlying mantle, causing a large amount of melting and, ultimately, the distinctive volcanism of Ahi Tupua. Key Points: We relocate 397 intermediate‐depth earthquakes beneath Ahi Tupua, central Taupō Volcanic Zone, and compute 47 focal mechanismsMost seismicity occurs within the slab crust and mantle, with subordinate mantle wedge and plate interface faultingHypocenters and focal mechanisms are consistent with slab‐derived fluid fluxing melting of the mantle wedge beneath Ahi Tupua [ABSTRACT FROM AUTHOR]

Mt. Ruapehu is an active andesitic stratovolcano, consisting of several peaks with the summit plateau at 2,797 m, making it the tallest active volcano in New Zealand. The extent of the volcano spreads 40 km across with a series of complex faults encompassing almost the entire base of the volcano. A series of earthquakes occurring 20 km west of the summit of Mt. Ruapehu, near the small town of Erua, which preceded the 1995/1996 major volcanic eruption sequence has been proposed as a medium-term precursor for eruptions at Mt. Ruapehu. We use unsupervised machine learning clustering algorithms HDBSCAN and DBSCAN to define anomalous earthquake swarms in the region and determine whether the Erua swarm was unique by identifying key characteristics in space, time and magnitude distribution. HDBSCAN found six spatial cluster zones to the west of Mt. Ruapehu, which have temporal seismic bursts of activity between 1994 and 2023. DBSCAN identified the seismic swarm that preceded the 1995/1996 major eruption, along with one other similar cluster in the same region, which did not coincide with any documented magmatic unrest, suggesting distal seismic swarms at Mt. Ruapehu may not serve as a reliable eruption precursor when observed in isolation. We instead found that earthquake swarms are relatively common at Mt. Ruapehu and the temporal evolution of the earthquake clusters west of Mt. Ruapehu share similar characteristics to seismic swarms identified in other settings related to fluid migration, typical of fault-valve models. [ABSTRACT FROM AUTHOR]

Accurate volcanic hazard assessments rely on a detailed understanding of the timing of past eruptions. While radiometric methods like 40Ar/39Ar or K/Ar are by far the most conventional lava flow dating tools, their low resolution for young (<20 ka) deposits interferes with the development of precise recent effusive chronologies on most volcanoes. Mt. Ruapehu (New Zealand) has produced many lava flows throughout its history, but the precise timing of many recent eruptions remains largely unknown. In this study, we use cosmogenic 3He exposure dating to provide 23 eruption ages of young lava flows at Ruapehu. We then compare our results with existing 40Ar/39Ar and palaeomagnetic constraints, highlighting the value of cosmogenic nuclides exposure dating in refining recent eruptive chronologies. Of the 23 sampled flows, 16 provided robust eruption ages (5–20 % internal 2σ; n≥3) between ca 20 and 8 ka, except for one lava erupted at around 43 ka, and their age distribution indicates that, during the last 20 thousand years, effusive activity at Ruapehu peaked at 17–12 ka and at 9–7.5 ka. Nearly identical eruption ages of lavas located in different flanks of the volcanic edifice suggest concurrent activity from multiple vents during relatively short time intervals (0–2 kyr) at around 13, 10 and 8 ka. We analysed four lavas previously dated by 40Ar/39Ar, two of which yielded eruption ages older than the older limit of the 2σ interval of the radiometric dates, but the good clustering of individual samples from our sites suggests that our results better represent these lava flows' real eruption ages. Our 3He-based dates show excellent agreement with palaeomagnetic constraints, suggesting that production rate uncertainties are unlikely to impact the accuracy of our eruption ages. This study demonstrates how cosmogenic nuclides dating can provide greater detail on the recent effusive chronology of statovolcanoes, helping to resolve the low resolution and difficulty in applying radiometric dating methods to young lava flows. [ABSTRACT FROM AUTHOR]

From 2005 to 2013, air sampling across the SW Pacific between Nelson, New Zealand and Osaka, Japan was undertaken by New Zealand's National Institute of Water and Atmospheric Research (NIWA) from MV Transfuture5, a 60,000 tonne bulk carrier owned and operated by Toyofuji Shipping Company. An average of two sampling voyages a year were carried out; on eight of these voyages aerosol sampling instrumentation was available to take on the ship. Condensation nuclei (CN) were measured using a TSI 3010 condensation particle counter (CPC). The aerosol data collected from 30°S through to Osaka have been analysed and the results previously published (Bromley et al, 2018). This paper discusses the data collected during the earlier section of the voyages from Port Nelson (41.35°S to 30°S). Sudden large increases in CN concentrations were detected on several voyages, in particular when the wind pattern was off the North Island of New Zealand, or from the Australian east coast. Back trajectories were compiled to examine possible sources of the enhanced CN concentrations, which included human activities, oil and gas commercial industrial activities and volcanic eruptions. Advection of aerosols into the coastal areas will cause enhanced signatures in the size distribution, composition and optical depths and can strongly influence the radiative coupling between ocean and atmosphere by scattering and absorbing solar radiation. [ABSTRACT FROM AUTHOR]

Hydrothermal eruptions are the most violent and hazardous phenomena within geothermal fields. The largest of these may produce kilometer-sized craters and breccia deposits that are tens of meters thick. The geological and hydrothermal priming that leads to these types of eruptions is poorly understood. To understand large hydrothermal eruptions, we investigated a series of prehistoric events at the Rotokawa geothermal field in New Zealand. By revising the stratigraphy and distribution of hydrothermal breccia deposits and correlating these with componentry, crater morphology, and subsurface geological structure, we estimated the frequency, priming processes, triggers, and dynamics of multiple eruptions. Seventeen large hydrothermal eruptions occurred centuries to millennia apart in the period from ca. 22 cal ka B.P. to ca. 3.4 cal ka B.P. Of six hydrothermal eruptions since ca. 7 ka, four produced oval-shaped craters up to 2 km in diameter, creating a broad, shallow depression within the geothermal field. The two youngest eruptions occurred northeast of earlier eruption centers and have narrower and elongated vents. We infer that in the central depression, newly formed craters rimmed by breccia deposits and high-relief country rock hosted temporary lakes tens of meters deep. Crater-lake breakout(s) and/or seismic events caused sudden pressure reduction above the hydrothermal aquifer, triggering hydrothermal eruptions. Northeast of the basin, hydrothermal alteration produced caprocks above intensively fractured areas. In this case, earthquakes are the most likely trigger for cap-rupture and eruption. All eruptions excavated shallow and large craters mostly within partially altered Oruanui Formation and pre-fragmented breccias. The size and localization of the eruptions was likely due to a combination of (1) availability of undisturbed porous ignimbrite hosting large thermal aquifers, (2) efficient crater excavation within or alongside pre-fragmented breccia, and (3) the location of fracture and fault zones that channeled deep fluid upflow, favoring priming processes. This study highlights how an interplay of tectonic, magmatic, and hydrologic processes is responsible for the timing, dynamics, and ultimate size of hydrothermal eruptions in geothermal fields. Some events may be very large and destructive depending on the right priming and geological conditions. [ABSTRACT FROM AUTHOR]

There are currently no quantitative short-term eruption forecasts based on peer-reviewed and validated models that are operational for New Zealand's volcanoes. Specific forecasts produced for work-risk assessments are not generally publicised. During a volcanic crisis, eruption forecasts are demanded under high stress and time-restricted conditions. Many forecasting options exist but none are proven as universally viable, with testing and calibration limited to the hindcasting of specific events. Here, we compare the requirements of six methods with currently available data and monitoring capabilities at each of New Zealand's volcanoes to determine which methods are currently feasible, as well as those options that may be implemented with additional effort or equipment. In New Zealand, the major limiting factor in method selection is the low number of past instrumentally monitored eruptions. This data gap may be filled by carefully selected analogue data from a global volcano set and expert knowledge. Event trees and the failure forecasting method may be set up at most volcanoes with minimal effort, but the latter can only forecast eruption onset time. Expert interpretation is the only method available in New Zealand for any forecast output type. [ABSTRACT FROM AUTHOR]

Using a network of global navigation satellite systems receivers in New Zealand, located 2,000–3,300 km southwest of Hunga Tonga‐Hunga Ha'apai volcano, we found at least three different kinds of ionospheric disturbances from changes in total electron contents (TEC). Ionospheric signatures of the near‐field acoustic wave propagating ∼0.8 km/s were not clear in New Zealand due possibly to large geometric decay. The first disturbance emerged ∼1 hr after the eruption and traveled toward southwest with a speed of ∼0.6 km/s. This, together with the subsequent disturbance propagating by ∼0.4 km/s, suggests its link to the ahead‐of‐tsunami ionospheric disturbance, excited by the Lamb wave and subsequent tsunamis traveling in the Pacific Ocean. The second disturbance started ∼2 hr after the eruption as tens of waves with periods 10–15 min propagating by ∼0.3 km/s, possibly internal gravity waves (IGW) excited by the passages of the Lamb wave. Such IGW wave trains continued until ∼10 hr after the eruption. The Lamb wave traveled round the earth, and its second and third passages disturbed the ionosphere in New Zealand on the next day as similar IGW wave trains following the Lamb wave. The third disturbance occurred as an enhancement of the harmonic oscillation of TEC with frequency of ∼3.7 mHz, ∼14 hr after the eruption. This might be an atmospheric mode excited by the eruption, but its propagation and sudden activation remain unexplained. Key Points: Long‐period disturbance emerged in New Zealand ∼1 hr prior to the arrival of the atmospheric Lamb wave, and propagated at ∼0.6 km/s and ∼0.4 km/s toward southwestRepeated passages of the atmospheric Lamb wave caused suites of internal gravity waves, propagating at ∼0.3 km/sAtmospheric mode of ∼3.7 mHz became stronger ∼14 hr after eruption in New Zealand [ABSTRACT FROM AUTHOR]

Volcano crater lakes, while picturesque, can sometimes mask the occurrence of small eruptions or hydrothermal fluid release events. However, these seemingly hidden events hold a wealth of valuable information about the underlying volcanic conduit and may pose risks to those near the volcano's summit. This study presents a novel method for identifying these hard‐to‐detect fluid release events by examining seismic data from Ruapehu volcano in New Zealand. We undertake a multi‐timescale template‐matching analysis that uses a newly discovered seismic eruption precursor, to identify patterns related to the rapid consolidation of hydrothermal seals, pressurization processes, and the subsequent release of hydrothermal fluids. As a result, we identified a potential instance of sudden fluid‐release events that were previously unnoticed due to the presence of the crater lake. Our findings support a conceptual model of cyclic pressure variation within the conduit beneath an active crater lake. This model involves the formation and disruption of seals, followed by depressurization through hydrothermal fluid release events. Fluid discharge recession recorded as seismic amplitude decay, provides information about the properties of the reservoir, conduit, and the fluid being discharged. We also applied this technique to Kawah‐Ijen (Indonesia) and Copahue (Chile‐Argentina), identifying multiple potential events at these volcanoes. These findings enhance our understanding of the conditions leading to explosive eruptions, including those that could breach the crater lake. Plain Language Summary: We analyzed seismic data from Ruapehu volcano (New Zealand) to improve volcanic event catalogs by locating signatures of rapid hydrothermal seal formation and failure. Events are detected temporally within the seismic record using an empirical model of sealing/pressurization/eruption proposed for Whakaari volcano in New Zealand. The approach allows us to identify fluid release events that might have been obscured by Ruapehu's crater lake or have been too small to be noticed by standard monitoring techniques. Our analysis has revealed several fluid release episodes, including reported eruptions, where a peak in displacement seismic amplitude ratio is followed by a sharp increase in real‐time seismic amplitude measurement and an exponential decay in the hours and days following the events. We model this decay using a linear dependence on the degassing rate, and exponential relaxation from a discharging linear reservoir. These findings can help us conceptualize the conditions leading to explosive, potentially lake breaching eruptions. Key Points: Volcano crater lakes can obscure volcanic fluid release eventsThrough volcano seismic data in a template‐matching approach, we identified short‐term sealing, pressurization, and fluid‐release pulsesWe identified several fluid‐released events at Ruapehu (New Zealand), Copahue (Chile/Argentina), and Kawah Ijen (Indonesia) volcanoes [ABSTRACT FROM AUTHOR]

The biggest volcanic eruption since 1991 happened on 15 January 2022 on the island of Hunga Tonga‐Hunga Haʻapai (20.6°S; 175.4°W) in the South Pacific between 4:00 and 4:16 UT. The updrafts from the eruption reached 58 km height. In order to observe its ionospheric effects, approximately 750 GNSS receivers in New Zealand and Australia were used to calculate the detrended total electron content (dTEC). Traveling ionospheric disturbances (TIDs) were observed over New Zealand 1.0–1.5 hr after the volcano eruption, with a horizontal wavelength (λH ${\lambda }_{H}$) of 1,525 km, horizontal phase velocity (CH ${C}_{H}$) of 635 m/s, period (τ) of 40 min, and azimuth (α) of 214°. On the other hand, TIDs were observed 2–3 hr after the eruption in Australia with λH ${\lambda }_{H}$, CH ${C}_{H}$, τ, and α of 922 km, 375 m/s, 41 min, and 266°, respectively. Using reverse ray tracing, we found that these GWs originated at z > 100 km at a location ∼500 km south of Tonga, in agreement with model results for the location of a large amplitude body force created from the breaking of primary GWs from the eruption. Thus, we found that these fast GWs were secondary, not primary GWs from the Tonga eruption. Key Points: The first TIDs observed over New Zealand and Australia originate at z > 160 and z > 100 km about 436 km southeast of the eruptionThis location agrees with model results for the body force created by the dissipation of primary GWs from the eruptionThe first TIDs observed over New Zealand and Australia are secondary, not primary, gravity waves from the eruption [ABSTRACT FROM AUTHOR]

Plagioclase phenocrysts in pre-historic andesites provide insight to the dynamics of magma formation and eruption at Taranaki volcano, New Zealand. The phenocryst population has a diversity of relic cores and a total in situ 87Sr/86Sr range of 0.70440–0.70486. Within-sample 87Sr/86Sr variations of 0.00018 to 0.00043 indicate that many phenocrysts are antecrysts and/or xenocrysts, derived from multiple crystal mush bodies. The Sr-isotopic differences in the phenocrysts of consecutive eruptions indicate that different magmas were tapped or formed on a centennial timescale. Most phenocrysts have multiple resorption/calcic regrowth zone(s) with elevated FeO* but invariant MgO zonation profiles. They likely record mafic melt inputs, and subsequent storage at elevated temperature caused re-equilibration of the Mg gradient. However, distinct rim types record different final pre/syn-eruptive magmatic conditions. Those in magmas erupted at 1030–1157 CE, 1290–1399 CE and 1780–1800 CE are characterised by resorption and calcic regrowth with sharp MgO and FeO* gradients. They record the entry of mafic melt into the system a few days or less before eruption based on Mg diffusion chronometry. In contrast, most phenocrysts erupted at 1755 CE, 1655 CE, and a few pre-1 ka events, have texturally uniform rims, compositionally consistent with closed-system crystallisation. This suggests alternating external and internal eruption triggers. Alternatively, the rate of magma reactivation via intrusion may dictate whether there was sufficient time for a mineralogical response to be recorded in part or all of the system. With respect to anticipating future eruptions, the plagioclase phenocrysts suggest multi-stage magma priming but rapid onset of the final trigger. [ABSTRACT FROM AUTHOR]

Palaeoecology provides critical data for establishing ecological 'baselines', which can guide restoration efforts and be used to assess ecosystem change. However, statistical analyses can be challenging because of the large number of methods available for establishing palaeoecological baselines combined with a lack of practical guidance, particularly around quantifying baselines that include natural variability. We contribute one solution by providing guidance and an R package baselines for using palaeoecological data to (i) define baselines and (ii) test for change over time that incorporates variability. These methods provide an alternative to single-taxon analyses and allow ecosystem complexity to be captured. We use published pollen records as case studies to demonstrate how to establish vegetation baselines for seven localities in New Zealand where relatively recent (c. 1280 AD) and near-simultaneous human settlement across the country allows background environmental disturbance in the pre-human era to be distinguished from anthropogenic disturbance. We present methods for calculating distance from initial sample, distance from baseline in ordination space, allowing incorporation of ecosystem variability, and analysis of rates of change over time using principal curves. We found conventional and Bayesian ordination methods yielded similar results and were effective at identifying change following human settlement, despite the potential for a positive mean-variance relationship to confound results. Principal response curves were most sensitive to a known period of vegetation disturbance caused by volcanic eruptions at two sites with tephra deposits. Our proposed methods, case study and R package baselines are designed to provide a suite of tools to encourage and enable palaeoecological data to be used by palaeoecologists to assess trajectories and change over time, and monitor whether historical management actions have facilitated a change in direction towards a desired baseline state. [ABSTRACT FROM AUTHOR]

Accurate dating of young eruptions from explosive volcanoes is essential for forecasting future eruptions and for defining the hazardscape of volcanic fields. However, precise dating of Quaternary eruptions is often challenging due to limited number of applicable dating methods or lack of datable eruptive phases. Moreover, small volume eruptions (e.g., monogenetic type), despite their significance on regional scale, have traditionally deserved less attention than their large volume counterparts. Puketerata is a maar-lava dome complex in the central Taupō Volcanic Zone (New Zealand), encompassing mafic and silicic phreatomagmatic eruptions with well-preserved pyroclastic deposits sourced from closely spaced vents. Its most recent activity is estimated to ca. 16 ka based on medial and distal stratigraphic surveys. Here, we carried out two independent age determinations and an additional paleomagnetic analysis on the volcanic succession of the Puketerata maar-lava dome complex with an aim to unravel the timing of volcanic activity. Combined U-Th disequilibrium and (U-Th)/He dating of zircon from two lava domes yielded eruption ages of 11.3 ± 2.6 ka and 11.3 ± 1.7 ka, which are concordant with the radiocarbon ages of 11.3–11.7 ka obtained on charcoal from the base of the pyroclastic sequence. Paleomagnetic data on the lavas from the two lava domes suggest at least ~ 100 years difference between their emplacements. Our geochronological results and new stratigraphic observations suggest that the volcanic/magmatic history of the Puketerata is complex with multiple eruptions within a small, confined area, where the most recent eruptions occurred only at ca. 11.5 ka, which is significantly younger than previously thought. This provides an additional datum for volcanic hazards assessment and stratigraphic correlations in New Zealand. [ABSTRACT FROM AUTHOR]

Stratospheric aerosol plays an important role in Earth's radiative balance. Systematic measurements of stratospheric aerosol number concentration and size are needed to characterize their baseline values and variability, improve understanding of aerosol microphysics, and assess the representation of stratospheric aerosol processes in global models. In situ measurements of particle size distribution provide insight into the responses of stratospheric aerosol processes to perturbations from volcanoes and wildfires, anthropogenic emissions from rockets and aircraft, or intentional injections related to climate intervention. The Baseline Balloon Stratospheric Aerosol Profiles (B2SAP) project uses compact, lightweight payloads carried by meteorological balloons to measure aerosol number density and size distributions, water vapor, ozone, and meteorological data from the surface to the middle stratosphere. The long‐term goal for the B2SAP project is to produce climatologies of aerosol number and size distributions into the middle stratosphere at latitudinally distributed measurement sites. Since March 2019, B2SAP payloads have been launched from Boulder, CO, USA once to twice per month and four to six times per year from Lauder, NZ. These measurements provide a new record of in situ stratospheric aerosol observations and are being used to help validate satellite‐based estimates of stratospheric aerosol size distributions. Here we present 50 vertical profiles from Boulder, CO, from March 2019 to March 2022, to build a NH mid‐latitude climatology of stratospheric aerosol and its variability and investigate the impact of natural perturbations on stratospheric aerosol microphysics. Plain Language Summary: Particles in the stratosphere play important roles in chemistry and climate. Lightweight instruments carried by weather balloons can provide systematic measurements of the particle number and size, atmospheric water vapor and ozone (two gases that also influence atmospheric chemistry and climate) to inform these areas of research. Without weather in the stratosphere, the sources and sinks of particles are few, and concentrations of particles change slowly over time, in the absence of powerful volcanic eruptions or large wildfires, which can inject or loft material into the stratosphere. Particularly in these cases, balloon‐borne observations can be critical to validating satellite retrievals and improving global climate models. As part of the Baseline Balloon Stratospheric Aerosol Profiles (B2SAP) project, weather balloon launches with the instruments described above have taken place from Boulder, CO, USA and Lauder, NZ since March 2019. Here we present 50 vertical profiles from Boulder, CO from March 2019 to March 2022, which are used to provide a new record (to produce a climatology) at midlatitudes in the in the northern hemisphere and investigate the impact of volcanic eruptions and large wildfires within this period. Key Points: Balloon‐borne measurements are used to build a northern hemisphere (NH) midlatitude climatology of stratospheric aerosol number density and sizeVariability of NH midlatitude stratospheric aerosol number density exhibits a minimum of a factor of ∼2 near 22 km altitude (θ = 550 K)NH Stratospheric aerosol perturbations during 2019–2022 are detected and characterized using aerosol microphysical properties [ABSTRACT FROM AUTHOR]

We investigate the oceanic and ionospheric response in New Caledonia‐New Zealand and Chile‐Argentina to the 15 January 2022 Hunga‐Tonga volcanic eruption. For the first time, we highlight a reversed response in the oceans and in the ionosphere in terms of the amplitudes. The sea‐surface fluctuations due to the passage of the atmospheric Lamb wave (i.e., air‐sea wave) were not remarkable while the related ionospheric perturbation was considerable. Reversely, the eruption‐induced tsunami ("regular" tsunami) caused major variations in sea‐surface heights (∼1 m near the volcano and ∼2 m along the Chilean coastline), whereas the associated ionospheric perturbation was quite small. The observed large‐amplitude ionospheric response due to Lamb waves propagation is difficult to explain, and the coupling between the Lamb wave and the ionosphere is not well‐understood yet. For the first time, we estimate the delay between the Lamb waves and their signatures in the ionosphere to be ∼12–20 min. Plain Language Summary: The eruption of Hunga‐Tonga volcano produced a variety of atmospheric and tsunami waves recorded all over the world. We study the impacts of the eruption together on the oceans and in the ionosphere in New Caledonia‐New Zealand (near the volcano) and Chile‐Argentina (far from the volcano). At the sea surface, we observe two phenomena causing sea‐height variations. The first is a small tsunami (air‐sea wave) created by the Lamb wave: the high‐pressure atmospheric wave triggered by the eruption. The second is the tsunami induced by the eruption itself. Spectacularly, at 300 km altitude, in the ionosphere, we observe perturbations in the electron content caused by the Lamb wave and by the regular tsunami. We are the first to report on the reversed amplitude of the two phenomena in the oceans and in the ionosphere. The sea‐surface perturbation caused by the Lamb wave was not significant, while ionospheric perturbation was considerable. In contrast, the regular tsunami wave produced major variations. For the first time, we estimate the time delay between the Lamb wave and its signature in the ionosphere. Key Points: Joint study of oceanic and ionospheric response in New Caledonia‐New Zealand and Chile‐Argentina to the 15 January 2022 volcanic eruptionNear‐surface propagating Lamb wave caused a small tsunami in the ocean (air‐sea wave) and unusually strong disturbances in the ionosphereInversely, the eruption‐generated tsunami showed significant wave heights in the ocean and much smaller response in the ionosphere [ABSTRACT FROM AUTHOR]

The Hunga Tonga‐Hunga Ha'apai (hereafter HTHH) submarine volcano erupted at 04:14:45 UT on 15 January 2022, causing ionospheric disturbances. This paper uses carrier phase observations from GNSS tracking stations in New Zealand and Australia to calculate the vertical total electron content. At 06:10, the ground‐based GNSS tracking station in New Zealand observes a maximum amplitude of 2.26 TECU anomaly caused by a mesoscale traveling ionospheric disturbance (MSTID) with a wavelength of 200–250 km, a period of 6–13 min, and a maximum propagation velocity of 330 m/s. The anomaly developed with time along the north‐south island direction toward the south island and lasted for about three and a half hours, with the ionosphere returning to pre‐eruption levels after 09:50, indicating a correlation between ionospheric activity and volcanic eruption. An ionospheric anomaly caused by an MSTID was also observed off the east coast of Australia around 08:11, with a maximum amplitude of 3.17 TECU and a maximum propagation velocity of 356 m/s. The ionospheric anomaly in Australia spreads out in a plane. In the process of propagation, it continuously impacts the area it passes through, and the entire anomaly process lasts for more than 7 hr. Still, the anomalous propagation velocities are more significant than in New Zealand, indicating that the Lamb waves excited by the eruption of the HTHH submarine volcano are directional in propagation speed; westward travels faster than southward. This finding will provide more references for scholars to study the mechanism and characteristics of anomaly propagation. Plain Language Summary: This paper reports on the Hunga Tonga‐Hunga Ha'apai submarine volcanic eruption event at Tonga on 15 January 2022, which caused air pressure waves in the form of Lamb waves to propagate to ionospheric heights and caused traveling ionospheric disturbances. Analysis of the filtered total electron content in the ionosphere using dense GNSS tracking stations in Australia and New Zealand revealed large‐scale, intense ionospheric disturbances. The propagation of the anomaly is also directional, with the New Zealand ionospheric anomaly initially propagating from north to south in a ripple pattern with a maximum mesoscale traveling ionospheric disturbance (MSTID) propagation velocity of ∼330 m/s. The impact of Lamb waves on the ionosphere in Australia is more pronounced, with the disturbance unfolding in a faceted pattern from east to west for up to 7 hr, during which the maximum MSTID propagation velocity is ∼356 m/s. In addition, the anomaly is affected by small‐amplitude gravity waves and excites multiple ionospheric disturbance phenomena during its propagation in both locations. This result confirms the natural phenomenon of ionospheric disturbances induced by extreme natural hazards and shows that severe explosive events can have a lasting and far‐reaching impact on the ionosphere. Key Points: Evidence of widespread traveling ionospheric disturbances caused by volcanic eruptionsThe propagation of the anomaly is directional, propagating westward at a greater rate than southwardSmall‐scale gravity waves have caused multiple transient ionospheric disturbances in both New Zealand and Australia [ABSTRACT FROM AUTHOR]

This paper investigates concentric traveling ionospheric disturbances (CTIDs) associated with the Tonga volcanic eruption. Results show that: (a) two types of CTIDs (CTID #1 and CTID #2) were identified that traveled radially from Tonga at the speed of 610–880 m/s (acoustic‐mode) and 300–380 m/s (Lamb‐mode), respectively. CTID #1 reached 3,800 and 5,000 km away from the eruption location toward the directions of New Zealand and Australia, respectively. CTID #2 propagated persistently for ∼9 hr over New Zealand and Australia. (b) The CTID #2 wavefront changed after 08:35 UT over New Zealand, possibly due to a combination of factors including the anisotropic propagation of CTID #2, the regional geomagnetic declination, and westward‐moving Lamb waves. (c) Topside total electron content (TEC) enhancement with a magnitude over two TECu was observed from COSMIC‐2 measurements. The enhancement agrees with CTID #1 peak from nearby ground‐based TEC observations and could be related to the upward propagation of the F layer's CTID #1 signatures. Plain Language Summary: The Tonga volcanic eruption on 15 January triggered various atmospheric waves that propagate from the Earth's surface and throughout the atmosphere and ionosphere. In this study, we discuss two types of concentric traveling ionospheric disturbances (CTIDs, #1 and #2) propagating outward from the Tonga site based on measurements collected by ∼1,000 ground‐based global navigation satellite system receivers. Our analysis based on the CTID propagation speed showed that CTIDs #1 and #2 traveled at acoustic and Lamb wave modes, respectively. We also analyzed COSMIC‐2 satellite radio occultation observations and showed that CTID #1‐related enhancement signatures were observed at the topside ionosphere near the eruption site. Moreover, it is interesting to note that CTID #2 wavefront changed over New Zealand after 08:35 UT on 15 January likely followed the regional geomagnetic declination and westward‐moving Lamb waves. Key Points: Two distinctive types of concentric traveling ionospheric disturbances (CTIDs #1 and #2) were identified, and they propagated radially outward from Tonga at the speed of 610–880 m/s (acoustic‐mode) and 300–380 m/s (Lamb‐mode), respectivelyThe wavefront of the long‐lasting CTID #2 changed after 08:35 UT over New Zealand, possibly due to the regional geomagnetic declination and westward‐moving Lamb wavesDistinctive total electron content (TEC) enhancement of over 2 TECu magnitude observed above 530 km near the eruption site could be associated with the upward propagation of the acoustic‐mode CTID #1 signatures in the F layer [ABSTRACT FROM AUTHOR]

Despite a rich history of botanical research, little is known about the distribution of genetic variation within New Zealand plant species. With a native vascular flora that consists of ∼80% endemics, nearly one-half of which are threatened, there is a dire need for a better understanding of intraspecific diversity for individual plant species and of biogeographic patterns for the wider New Zealand flora. To these ends, we have investigated population genetic structure in the endemic root holoparasite, Dactylanthus taylorii (pua o te Rēinga, Mystropetalaceae). A total of 235 individuals from 31 locations across the North Island of New Zealand (Te Ika-a-Māui, Aotearoa) were genotyped for a suite of nuclear microsatellite loci. Genotype data were analysed at the individual and population levels to assess genetic diversity within and among populations and to investigate the geographic distribution of genetic variation within the species. Population structure was assessed using Bayesian clustering, discriminant analysis of principal components, and a Neighbor-Net analysis. A hierarchical pattern of genetic diversity was revealed, with evidence for three broad geographic regional groupings (West, East, and Central Volcanic Plateau (CVP)). Upon further analysis, each of the three geographic groups further subdivide hierarchically into two or three genetic subgroups. Genetic diversity was found to be relatively high in this endangered species but varies considerably across populations. The distribution of genetic groups appears to have been influenced by past volcanic activity as the CVP group is largely coincident with a distinct tephra isopach from the 1.8 ka Taupō eruption and the West and East groups may have diverged due to recurring volcanic activity in the Central Volcanic Zone. The genetic structure resolved here provides important information for the management of D. taylorii specifically and for our understanding of New Zealand biogeography generally. [ABSTRACT FROM AUTHOR]

The Hunga-Tonga volcanic eruption occurred on 15 January 2022 generated different modes of atmospheric and ionospheric waves. Using the Geostationary Operational Environment Satellite-17 (GOES-17), Aqua and Global Positioning System (GPS) satellite observations, an atmospheric and ionospheric multi-layer study of the Tonga volcano induced signatures over the New Zealand region is performed. The visible and infrared channel data of GOES-17 and Atmospheric Infrared Sounder (AIRS) data from NASA Aqua satellite confirm the presence of a highly convective zone and occurrence of concentric Lamb and gravity waves at lower atmospheric altitudes. The Total Electron Content (TEC) derived from 175 GPS stations covering the entire New Zealand region brings out two dominant modes of Travelling Ionospheric Disturbances (TIDs) having periodicity between 30 and 50 min. These two different modes having the phase speeds of 542 m/s and 354 m/s are allied to atmospheric gravity waves and Lamb wave triggered gravity waves respectively and are observed to propagate towards the south-west direction over the New Zealand region. [ABSTRACT FROM AUTHOR]

Kiwi are a unique and emblematic group of birds endemic to New Zealand. Deep-time evolutionary relationships among the five extant kiwi species have been difficult to resolve, in part due to the absence of pre-Quaternary fossils to inform speciation events. Here, we utilise single representative nuclear genomes of all five extant kiwi species (great spotted kiwi, little spotted kiwi, Okarito brown kiwi, North Island brown kiwi, and southern brown kiwi) and investigate their evolutionary histories with phylogenomic, genetic diversity, and deep-time (past million years) demographic analyses. We uncover relatively low levels of gene-tree phylogenetic discordance across the genomes, suggesting clear distinction between species. However, we also find indications of post-divergence gene flow, concordant with recent reports of interspecific hybrids. The four species for which unbiased levels of genetic diversity could be calculated, due to the availability of reference assemblies (all species except the southern brown kiwi), show relatively low levels of genetic diversity, which we suggest reflects a combination of older environmental as well as more recent anthropogenic influence. In addition, we suggest hypotheses regarding the impact of known past environmental events, such as volcanic eruptions and glacial periods, on the similarities and differences observed in the demographic histories of the five kiwi species over the past million years. [ABSTRACT FROM AUTHOR]

The tsunami that occurred after the Hunga Tonga-Hunga Ha'apai volcano eruption on 15 January 2022 was unusually fast and large, particularly at large distances from the source. Here we use an observation-calibrated air-wave model to generate ocean waves using a tsunami model. We used pressure data observed at 94 stations in Niue, the Cook Islands, and New Zealand's main and outer islands to obtain a simple air-wave model. The modelled air-wave travels at an approximated constant speed of 317 m/s with an amplitude that decays with distance from the volcano. We then simulated the generation and propagation of tsunami due to the propagating air-wave in the atmosphere above the ocean. The leading sea surface displacement excited by the pressure disturbances travels at the same speed as the air-wave. This leading wave is then followed by subsequent water waves that travel in the same direction as the leading wave but at the conventional tsunami propagation speed. In the model, the air-wave was more effective at generating a tsunami when it travelled over a deep bathymetric feature like the Kermadec-Tonga Trench. The tsunami amplitudes observed at gauges do not decay as rapidly with distance from the volcano as would be expected for a localized tsunami source. This is due to the continuous excitation of the tsunami as the air-wave propagates across the ocean. In shallow water, the leading water surface displacement can often be much smaller than the later waves that were most likely to have been generated in the deep ocean. A better understanding of the complexity of tsunami generation and propagation of this kind is important to help improve future tsunami disaster mitigation from such sources. [ABSTRACT FROM AUTHOR]

Much of our knowledge about the impacts of volcanic eruptions on climate comes from proxy records. However, little is known about their impact on the low to mid-latitudes of the Southern Hemisphere. Using superposed epoch analysis, we investigated whether volcanic signals could be identified in annual tree-ring series from eight New Zealand dendrochronological species. We found that most species are reliable recorders of volcanic cooling and that the magnitude and persistence of the post-event response can be broadly linked to plant life history traits. Across species, site-based factors, particularly altitude and exposure to prevailing conditions, are more important determinants of the strength of the volcanic response than species. We then investigated whether chronology selection impacts the magnitude of post-volcanic cooling in tree-ring-based temperature reconstructions by developing two new multispecies reconstructions of New Zealand summer (December–February) temperature with one reconstruction from the pool of all available chronologies, and the other from a selected subset shown to be sensitive to volcanic eruptions. Both reconstructions record temperature anomalies that are remarkably consistent with studies based on instrumental temperature and the ensemble mean response of climate models, demonstrating that New Zealand ring widths are reliable indicators of regional volcanic climate response. However, we also found that volcanic response can be complex, with positive, negative, and neutral responses identified – sometimes within the same species group. Species-wide composites thus tend to underestimate the volcanic response. This has important implications for the development of future tree-ring and multiproxy temperature reconstructions from the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Understanding the stress evolution of extinct volcanoes can improve efforts to forecast flank eruptions on active systems. Field, petrographic, and seismic data are combined with numerical modeling to investigate the paleo‐stress field of New Zealand's Akaroa Volcano, or Akaroa Volcanic Complex. Field mapping identifies 86 radially oriented dikes and seven lava domes found only within a narrow elevation range along Akaroa's erosional crater rim. These observations suggest that crater rim dike emplacement resulted from lateral deflection of vertically ascending intrusions from a centralized magma source, which in turn may have facilitated formation of the lava domes, as well as two scoria cones. We postulate that dike deflection occurred along a stress barrier, as neither a compositional change nor structural boundary are present. We use a finite element model (FEM) simulating Akaroa to test how different factors may have influenced the system's stress state and dike geometry. Elastic, non‐flexural ("roller") model configurations containing a large, oblate, and shallow magma chamber produce stress barriers most conducive to radial dike emplacement along Akaroa's crater rim. These configurations also simulate rapid edifice construction above a preexisting lithospheric "bulge." Conversely, simulating flexural stresses exerted on the lithosphere by Akaroa's large mass hinder rather than promote radial dike emplacement. Temperature‐dependent viscoelastic relaxation promotes gradual increases in stress barrier elevation, though this effect is strongly dependent on magma chamber parameters. These results suggest that Akaroa was constructed rapidly (within ∼100 kyr) prior to crater rim dike emplacement, which occurred throughout the volcano's remaining active lifespan. Plain Language Summary: Fully understanding how magma moves within active volcanoes requires scientists to study solidified remnants of once‐molten magma "plumbing systems" that have been unearthed by the erosion of extinct (i.e., no longer active) volcanoes. Here we present new observations of New Zealand's Akaroa Volcano, an extinct volcanic mountain or "edifice" built from lava eruptions and underground magma movement that occurred in multiple regions rather than one central summit vent. Observations include on‐the‐ground measurements of rock formations, microscope analysis of rock samples, satellite‐derived elevation data, and underground properties inferred from earthquake‐generated seismic waves. We incorporate these observations into a computer model of the once‐active volcano to understand why magma followed the paths it did, erupting on Akaroa's sides, or flanks, rather than its central summit region. Based on the results of our computer model, these eruptions occurred throughout Akaroa's one‐million‐year lifespan, after the volcano itself was constructed in the geologically "brief" period of roughly 100,000 years. Our computer simulations also provide a framework for improving scientists' assessments of future eruption risks on the slopes of active volcanoes with a similar shape and chemical composition to Akaroa, such as Sicily's Mt. Etna or the Galapagos' Fernandina volcano. Key Points: Field, petrographic, and seismic observations constrain the formation of dikes, lava domes and scoria cones on Akaroa Volcano's crater rimTwo‐dimensional axisymmetric finite element model (FEM) indicates a stress barrier may have promoted radial dike emplacement along Akaroa's crater rimOptimal stress barriers occur in elastic, non‐flexural FEMs with large, shallow, oblate chamber and edifice rapidly built on inclined bulge [ABSTRACT FROM AUTHOR]

Forecasting future destructive eruptions from re‐awakening volcanoes remains a challenge, mainly due to a lack of previous event data. This sparks a search for similar volcanoes to provide additional information, especially those with better compiled and understood event records. However, we show that some of the most obviously geologically comparable volcanoes have differing statistical occurrence patterns. Using such matches produces large forecasting uncertainties. We created a statistical tool to identify and test the compatibility of potential analogue volcanoes based on repose‐time characteristics from world‐wide datasets. Selecting analogue volcanoes with compatible behavior for factors being forecast, such as repose time, significantly reduces forecasting uncertainties. Applying this tool to Tongariro volcano (NZ), there is a 5% probability for a Volcanic Explosivity Index (VEI) ≥ 3 explosive eruption in the next 50 years. Using pre‐historic geological records of a smaller available set of analogs, we forecast a 1% probability of a VEI ≥ 4 eruption in the next 50 years. Plain Language Summary: Probabilistic forecasts of future destructive eruptions from re‐awakening volcanoes can inform decision‐making to help mitigate volcanic risk. However, a lack of data describing previous events at many volcanoes hinders robust forecasts. Often, the only available forecasts are those based on expert judgment and knowledge of other similar but better known volcanoes. We show that eruption forecasting based only on comparisons of geological criteria produces large uncertainties. We created an alternative statistical tool to identify and test the compatibility of potentially analogous volcanoes based on the time between successive eruptions from individual volcanoes worldwide. Selecting volcanoes with analogous statistical features in terms of the time breaks between successive eruptions significantly reduces the uncertainty of eruption forecasts. We applied this tool to forecasting explosive eruptions at NZ Tongariro volcano using two sets of analogs we identified and found a 5% probability of a Volcanic Explosivity Index (VEI) ≥ 3 eruption and 1% probability of a VEI ≥ 4 eruption in the next 50 years. Key Points: We create a statistical tool to identify potential analogue volcanoes based on repose‐time characteristics from world‐wide datasetsAnalogs selected by this tool significantly reduce forecasting uncertainties compared to using analogs selected by geological similarityWe apply this tool to forecasting explosive eruptions at Tongariro volcano in New Zealand [ABSTRACT FROM AUTHOR]

Microlite crystallization in erupting basalt can occur in the conduit, in flight, or in situ after deposition. Distinguishing the products of primary versus secondary (post-fragmentation) crystallization can be challenging in near-vent environments, but is vital for interpreting shallow conduit conditions from pyroclast textures. Here, we examine pyroclasts of the 1886 basaltic Plinian eruption of Tarawera volcano, New Zealand, to assess the roles of primary versus secondary crystallization of microlites. Lapilli and ash were selected from (a) an ultra-proximal section (T47), < 100 m from vent, which is dominated by pyroclasts derived from the Plinian jet and column margin, and (b) a medial fall deposit section (T43), 2.5 km from the fissure, which contains products from the umbrella cloud. Strong contrasts in pyroclast groundmass crystallinities exist between sections, from near-holocrystalline (90–97% void-free corrected; VFC) in T47 pyroclasts to highly crystalline (77–83% VFC) in T43 pyroclasts. Subhedral-euhedral Fe–Ti microlites (< 3 μm) are ubiquitous and abundant in T47 pyroclasts, whereas they are virtually absent in T43 pyroclasts. Olivine is present in both T47 and T43 pyroclasts but evidence of its subsolidus transformation is only seen in T47 clasts, whereas in T43 clasts olivine is fresh. Near-complete crystallization of the groundmass and subsolidus transformation of olivine in the ultraproximal T47 clasts are evidence that post-depositional modification of primary pyroclast textures occurred in ultra-proximal environments at Tarawera as a response to high residual temperatures and oxidizing conditions, aided by short transport times of relatively coarse ejecta at high accumulation rates, likely supplemented by intense vent-derived heat. Ultra-proximal basaltic eruption products can continue to crystallize after deposition and are thus unlikely to be faithful indictors of shallow conduit magmatic processes; we recommend the use of medial and distal products instead. [ABSTRACT FROM AUTHOR]

Detailed knowledge of the pre-eruptive time scales associated with magma storage and transport is vital to improve volcanic hazard forecasting in active volcanic regions. However, quantification of the timescales of volcanic processes at mafic volcanic centres in continental intraplate settings is challenging, despite them being a source of significant hazards for human populations and infrastructure due to their limited predictability in space and time. We conducted a detailed petrological study to investigate the time scales of olivine storage and transfer throughout the eruption sequence of Waitomokia Volcanic Complex, a tuff ring and scoria cone complex in the Auckland Volcanic Field. Olivine crystal textures and compositions were determined from stratigraphically-constrained samples of the volcanic complex, from the initial phreatomagmatic phase to the final magmatic phase. Olivine crystals are typically <300 μm in length and characterised by skeletal morphologies, displaying chemical zoning in forsterite (Fo = 100*Mg/[Mg + Fe]; mol%), CaO, MnO and NiO wt% contents. We classified olivine into three major groups based on their Fo core compositions: (1) normally zoned crystals with high Fo content (Fo > 85), (2) crystals with intermediate Fo contents (84–81), and (3) reversely zoned crystals with lower Fo core content (<80). Olivine chemical zoning (diffusion) profiles were modelled in the context of a specific magmatic environment linked with changes in thermodynamic variables during storage (temperature, pressure, and oxygen fugacity). We propose that the normally zoned olivine crystals grew in one magmatic environment (ME1), which subsequently intruded into a more evolved (lower MgO) environment (ME2), where they interacted and were stored for up to 135 days before their eruption. During magma ascent to the surface, a second magma mixing event occurred between ME2 and magma within a third magmatic environment (ME3), forming reversely-zoned olivine crystals yielding notably shorter ascent times of approximately a few days. The rocks from the opening phreatomagmatic phase of the eruption show a larger range in olivine group types compared to the final magmatic phase, where those from the deeper ME1 are more abundant. The short time scales of magma transport obtained in our study, on the order of days to months, should be informative of the warning times that may be encountered between the onset of volcanic unrest and an eruption in the Auckland Volcanic Field. • Stratigraphically controlled sampling to unveil the magmatic system feeding monogenetic volcanoes. • The textures and zonings of olivine crystals provided constraints on the storage and pathway to the surface. • Diffusion chronometry on olivine related to the entire eruptive sequence. • Olivine diffusion revealed time scales of magmatic processes ranging from days to a few months. [ABSTRACT FROM AUTHOR]

Volcanic eruptions that occur without warning can be deadly in touristic and populated areas. Even with real-time geophysical monitoring, forecasting sudden eruptions is difficult, because their precursors are hard to recognize and can vary between volcanoes. Here, we describe a general seismic precursor signal for gas-driven eruptions, identified through correlation analysis of 18 well-recorded eruptions in New Zealand, Alaska, and Kamchatka. The precursor manifests in the displacement seismic amplitude ratio between medium (4.5–8 Hz) and high (8–16 Hz) frequency tremor bands, exhibiting a characteristic rise in the days prior to eruptions. We interpret this as formation of a hydrothermal seal that enables rapid pressurization of shallow groundwater. Applying this model to the 2019 eruption at Whakaari (New Zealand), we describe pressurization of the system in the week before the eruption, and cascading seal failure in the 16 h prior to the explosion. Real-time monitoring for this precursor may improve short-term eruption warning systems at certain volcanoes. Volcanic eruptions that occur without warning can be deadly in touristic and populated areas. Using a machine learning approach, the authors here discover distinctive patterns hidden in the seismic signals of a number of New Zealand and Alaskan volcanoes, that occur before most of the eruptions studied. [ABSTRACT FROM AUTHOR]

Arc magmas typically contain phenocrysts with complex zoning and diverse growth histories. Microlites highlight the same level of intracrystalline variations but require nanoscale resolution which is globally less available. The southern Taupo Volcanic Zone (TVZ), New Zealand, has produced a wide range of explosive eruptions yielding glassy microlite-bearing tephras. Major oxide analyses and textural information reveal that microlite rims are commonly out of equilibrium with the surrounding glass. We mapped microlites and microcrysts at submicron resolution for major and trace element distributions and observed three plagioclase textural patterns: (1) resorption and overgrowth, (2) oscillatory zoning, and (3) normal (sharp) zoning. Pyroxene textures are diverse: (1) resorption and overgrowth, (2) calcium-rich bands, (3) hollow textures, (4) oscillatory zoning, (5) sector zoning, (6) normal zoning and (7) reverse zoning. Microlite chemistry and textures inform processes operating during pre-eruptive magma ascent. They indicate a plumbing system periodically intruded by short-lived sub-aphyric dykes that entrain microantecrysts grown under diverse physico-chemical conditions and stored in rapidly cooled, previously intruded dykes. Changes in temperature gradients between the intrusion and the host rock throughout ascent and repeated magma injections lead to fluctuations in cooling rates and generate local heterogeneities illustrated by the microlite textures and rim compositions. Late-stage degassing occurs at water saturation, forming thin calcic microcryst rims through local partitioning effects. This detailed investigation of textures cryptic to conventional imaging shows that a significant proportion of the micrometre-sized crystal cargo of the TVZ is of antecrystic origin and may not be attributed to late-stage nucleation and growth at the onset of volcanic eruptions, as typically presumed. [ABSTRACT FROM AUTHOR]

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 Pamukçu 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. [ABSTRACT FROM AUTHOR]

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-doublecouple 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 [ABSTRACT FROM AUTHOR]

The complex volcanology and petrology of the Whakamaru volcanic deposits in Aotearoa New Zealand have thus far obscured the number of eruptive phases and the relative timing of these eruption(s). We investigate pumice clasts from multiple localities to elucidate the relative timing of the eruptions, with a focus on the pre-eruptive conditions of the melt-dominated magma bodies that fed the Whakamaru eruptions and on the mushes from which these magmas were extracted. Paired whole-rock and glass compositions confirm four magma types erupted during the Whakamaru eruptions (types A, B, C, D; originally identified by Brown et al., 1998). Using the glass compositions of the pumice clasts, we calculate pre-eruptive storage temperatures (using zircon saturation geothermometry) and pressures (using rhyolite-MELTS geobarometry). Using matching whole-rock compositions from a subset of pumice clasts, we calculate extraction pressures from magma mush (also using rhyolite-MELTS geobarometry). Pre-eruptive storage pressures estimate the depths where melt-dominated magma bodies were located prior to eruption; extraction pressures, in contrast, estimate the depths at which melt was extracted from magma mush to form melt-dominated magma bodies at shallower levels of the crust. Magmas were stored at shallow depths (∼50-150 MPa) prior to eruption. Extraction pressures for types B and C are well constrained to 155-355 MPa (with an assemblage including plagioclase and quartz). Extraction pressures for types A and D depend on oxygen fugacity (f O2), as the extraction assemblage includes plagioclase and orthopyroxene (170-290 MPa for ΔNNO = 0 to +0.5 and 290-360 MPa for ΔNNO = +1 to +1.5). The four magma types likely represent independent magma bodies, with these melt-dominated magma bodies stored shallower than and separate from the mush. At least two different magma subsystems fed the Whakamaru eruptions – one subsystem sourced the type A and type D magmas, while the other sourced the type B and type C magmas. The distribution of magma types recorded in the ignimbrite deposits and in the correlated tephras (Harmon et al., 2024) reveal the sequence of eruption for the four different mappable ignimbrites. The ignimbrites to the east of the caldera (Rangitaiki ± Te Whaiti) erupted before the Whakamaru ignimbrite (sensu stricto) to the west of the caldera. The youngest Whakamaru ignimbrite eruptions likely deposited to the northwest of the caldera contemporaneously with the Manunui ignimbrite to the west of the caldera. The combination of petrological data from the ignimbrites and associated tephras suggest a complex system that included laterally juxtaposed melt-dominated magmas as well as laterally juxtaposed magma mushes that spanned much of the shallow crust, but with regions in which magma appeared in low concentration or was entirely absent. This complex pre-eruptive architecture probably contributed to the complex eruptive patterns observed for the Whakamaru eruptions. • Four magma types sourced the Whakamaru eruptions with different combinations of magma types erupted at different stages • Modeled magma storage depths reveal shallow, upper crustal magma storage levels (∼ 50-150 MPa) prior to eruption • Modeled magma extraction depths reveal that two distinct magma subsystems sourced the Whakamaru group eruptions • The timing of the ignimbrite eruptions is established using correlation with pyroclastic fall deposits • Volcanology and petrology of the Whakamaru eruptions indicate complex pre-eruptive crustal architecture and eruption history [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]

We explore how volcanic hazards in a silicic volcanism-dominated caldera systems can be assessed by spatial and spatio-temporal statistical models using similar treatment to that applied to dispersed mafic monogenetic volcanic fields. The central part of the Taupo Volcanic Zone is an ideal location for such study, containing more than 300 small to medium volume eruptions identified as having occurred in the past 350 kyr. The spatial distribution of vents with respect to the location of faults indicates a very strong local tectonic control on new vent openings, which commonly manifests in eruptions characterized by fissure vents. Kernel density estimates, along with the migration of volcanic foci in the last 100 kyr, suggest the bipartition of the caldera system activity, separated by an approximately 20 km wide vent-free section of the Taupo rift between the Waikato River and the southern extent of the Kapenga caldera. The heterogeneity in the spatial pattern of vents in the vicinity of different calderas suggests that the caldera structures themselves exert considerable infuence on the location of post-caldera volcanism. The spatio-temporal analysis fails to identify a local maxima of spatio-temporal intensity corresponding to post-Oruanui volcanism of Taupo volcano, in contrast to that observed at Maroa and Okataina Volcanic Centres. This deficit of events indicates that the Taupo caldera system is behaving atypically, relative to the post-caldera stage of other calderas of the Taupo Volcanic Zone. [ABSTRACT FROM AUTHOR]

Tectonic hazards have profoundly influenced Māori relationships with, and understandings of, the environment, with oral histories and ethnographic records referencing recurring encounters with volcanic eruptions, earthquakes, and tsunamis across Aotearoa-New Zealand. This research works alongside members of the Māori kin-group Ngāti Kuri to deliberate and compare active oral histories with two ethnographic records that potentially refer to ancestral experience with past tsunami(s) in the Kaikōura region. It applies an inductive-based methodology informed by "collaborative storytelling," with the intent to appreciate the manner in which Ngāti Kuri interpret their past and present. The research affirms past catastrophic saltwater inundations and potential tectonic disturbances in the Kaikōura region. It also affirms that ethnographic records are not necessarily full or accurate accounts of historical events. The accounts presented here contribute to the reclaiming of Ngāti Kuri histories and point to new plural learning opportunities about coseismic tsunami hazard and history across the region. [ABSTRACT FROM AUTHOR]

The Taupo Volcanic Center [TVC; Taupo Volcanic Zone (TVZ), New Zealand] is home to the two most recent silicic caldera-forming eruptions in the TVZ—the giant (530 km3 DRE) Oruanui supereruption and the large (35 km3 DRE) Taupo eruption. This offers a unique opportunity to investigate similarities and differences between large and supersized volumes of rhyolitic magma at the TVC and more generally. We combine information from crystal textures (crystal size distributions), crystal compositions (Ti-in-quartz diffusion chronometry), and glass compositions (rhyolite-MELTS geobarometry) to investigate the crustal storage conditions, longevity, and eruption of these magmas. Results show differences between the storage depths of the Oruanui and Taupo magmas consistent with the differences in their glass silica contents but strikingly similar, short crustal residence times for the final crystal-poor, eruptible magma bodies (decades to centuries). Differences in groundmass textures between the two systems also likely reflect differences in ascent durations, decompression paths, and/or amounts of undercooling experienced by these systems due to the differences in their storage depths. Finally, comparing the evolution of storage depths and magma compositions at the TVC with those in a preceding central TVZ ignimbrite 'flare-up' supports the idea that the modern TVC may be flaring up and highlights the evolution of magma storage depths with increasing system maturity in this volcanic region. [ABSTRACT FROM AUTHOR]

The andesitic Tongariro Volcanic Complex in the Central North Island of New Zealand comprises tens of vents along an actively extending graben. Past work has hypothesised that multiple vents may operate during a single explosive eruption episode, providing an unprecedented hazard challenge for this region. The stratigraphic record suggests an irregular clustering of eruption episodes over time, including an unusual ≤ 200-year-long period from ~11.3–11.1 ka when several large explosive eruptions occurred. We carried out new field mapping, stratigraphy, and sedimentology of the resulting pyroclastic deposits to identify seven episodes during this period, locating the vent sites and calculating their climactic dynamic properties. Five of the episodes involved two or more vent locations that produced separate sub-Plinian/Plinian eruption columns. Eruption columns ranged between 16 and 24 km high and erupted volumes of 0.05 to 0.76 km3, indicating magnitudes of 4 to 5. Each of these episodes show north-to-south "unzipping" of the Tongariro Graben, with episodes beginning in northerly vents, before being joined by vents south of these. This included two scenarios; northern edifice vents followed by central edifice ones or central edifice vents followed by southern ones. In both cases, the northerly vents generally display the greatest peak eruption magnitudes and the steadiest eruptions. By contrast, the southernmost vents formed along a fault-controlled fissure-like system. These produced unsteady plumes and pyroclastic density currents. The northward widening tectonic graben structure thus influences the pattern and style of these Plinian-style eruptions. This study highlights a real possibility for an extreme hazard scenario involving successive large-scale eruptions at volcanic systems in slowly rifting environments and sheds new light on the volcano-tectonic interaction in such settings. [ABSTRACT FROM AUTHOR]

Restoration efforts around New Zealand provide safe havens for native species that have been seriously compromised since the arrival of people and introduced mammals approximately 750 yrs ago. Maungatautari in the Waikato is currently the largest area of almost (except for mice) mammal-free estate on the New Zealand mainland. We examined attributes, such as beetle size variation, dispersal ability and trophic structure, of the beetle community at Maungatautari and compared it with the fossil beetle assemblage from two central North Island sites where forest was preserved under up to 2 m of tephra and volcanic ash from the Taupo eruption (232 ± 5 AD (1718 ± 5 cal. yr BP)) prior to the introduction of mammals. A total of 334 fossil, and 206 extant, beetle species were found. No difference was observed between the trophic composition and dispersal ability of taxa within the beetle communities sampled from pre-mammal ecosystem compared with Maungatautari. Greater numbers of large species were found at Maungatautari compared to the two fossil sites. However, this disguised the loss of several large flightless ground-dwelling weevil species that were found as fossils but are now considered extinct. Surprisingly, only 1.2% of the fossil beetle species identified are now thought to be extinct. The fossil beetle assemblages from the central North Island are invaluable datasets that describe the pre-mammal beetle fauna and provide an important benchmark for assessing restoration outcomes in New Zealand forest ecosystems. [ABSTRACT FROM AUTHOR]

This study examined long-term stability in water quality of Lake Okataina, North Island, New Zealand, inferred from sediments deposited from 1836 to 2009, during which time there was a pyroclastic volcanic eruption (Tarawera 1886) and successive introductions of invasive mammals. Multiple geochemical proxies were analysed stratigraphically for organic matter loading, primary productivity, redox potential and phosphorus retention capacity. Organic matter loading to the lake is mostly authochthonous (algae) although there was increased allochthonous (terrestrial) loading immediately after the Tarawera eruption. After 1920, there was a sustained increase in inorganic erosion flux. Primary productivity appeared to increase considerably about 1960, but has remained relatively unchanged more recently. Our results suggest that the lake could recover from the impact of the volcanic eruption within a few decades, but the introduction of mammals may affect its resilience and lead to more pervasive impacts on the biogeochemistry. [ABSTRACT FROM AUTHOR]

A volcanic regime classifies a specific volcanic hazard state during which eruption episodes and events share similar frequency, magnitude, composition, and style. The post-AD 960 Maero Eruptive Period (MEP) at Mt. Taranaki (New Zealand) exemplifies such a distinctive eruptive period of volcanism. The deposits from intermittent eruptive episodes during this period built a pyroclastic fan on the northwestern flanks of the volcano. These deposits correlate to fall and thin pyroclastic density current deposits on other flanks. We have defined a sequence of 11 events via stratigraphy, radiocarbon dating, and geochemical studies. Each MEP episode involved lava dome growth and destruction from the summit crater. The deposits of the first MEP eruption episode cover deep palaeosols formed during a ~ 7000-year gap in activity on the NW volcano flanks. The first lava domes breached the western crater rim, and a large portion of the rim collapsed during the Newall episode c. AD 1360. This gave rise to increasingly hot and widespread block-and-ash flows. During the MEP, changes in magma composition reflect magma injection and mixing processes in small reservoirs. The episodes are classified into four scenarios, from high to low hazard impact: (1) dome collapse leading to Subplinian eruption, (2) explosive dome destruction and directed blast, (3) repeated rapid dome growth and large-scale hot dome collapse, and (4) slow dome effusion and partial collapse. The MEP defines a distinct volcanic regime, with the interval between the most recent MEP eruption and present > 50 years longer than any previous gaps between MEP episodes. As such, volcanic mitigation and forecasting at Taranaki must consider changes in hazard type if the current regime comes to an end. [ABSTRACT FROM AUTHOR]

Geological mapping in volcanic terrains is a challenging task as there needs to be input from various geologists' groups and only limited, often ambiguous guidelines exist. Volcanoes and volcanic successions are in many ways viewed and treated differently than normal sedimentary successions. Volcanic systems are very much a part of the normal sedimentary environment and as such need to integrated into the stratigraphic framework of the enclosing deposits. Most volcanoes supply large volumes of material (pyroclasts) into the sedimentary system. The type and style of eruption determines the time frame of the process, while the type of volcano defines the interaction between volcano and background sedimentation (e.g. monogenetic versus polygenetic volcanic systems). A sound lithostratigraphic framework for mapping geological units in volcanic terrains should also adopt the latest developments in volcanology and understanding of volcanic systems. The lithostratigraphic classification needs to define the mapping unit and apply it to the 1) proximal to distal volcanic facies, 2) eruption styles and their temporal changes, and 3) mode of pyroclast transportation (i.e. fallout versus pyroclastic density current). Differentiation of syn- and post-eruption re-sedimentation, during either within- or between eruptive phases, will determine the most useful stratigraphic nomenclature system to apply to the volcanic units. The approach to geological mapping in ancient and modern volcanic terrains can be different but the same basic stratigraphic principles and classification apply. The purpose of the geological mapping project, whether it be in ancient or modern volcanic systems, will define the style and scale of mapping. The type of output depends upon the objectives and available resources, including the volcanological experience of the mapping team. Here we provide some insight from a New Zealand perspective to geological mapping on active volcanic terrains in a convergent plate margin. • Volcanic systems are integrated part of the normal sedimentary environment. • A sound lithostratigraphic framework for mapping geological units in volcanic terrains should also adopt the latest developments in volcanology. • Geological mapping of volcanoes and the resulting maps should not violate basic geological mapping and stratigraphic principles. • The scale and the purpose of the geological map will largely define the methods used and the detail required in that volcanic terrain. • The formal volcanic stratigraphic units should follow basic volcano concepts and distinguish fallout deposits from gravity current successions. [ABSTRACT FROM AUTHOR]

The Whakamaru group eruptions (349 ± 4 ka; Downs et al., 2014) are the largest known eruptions in the history of the young Taupō Volcanic Zone, Aotearoa New Zealand. The complex field relationships of the ignimbrites have thus far obscured the timing and history of their eruption(s). We present new evidence from fall deposits correlated with the Whakamaru eruptions to complement the ignimbrite record. Two coastal sections are characterized in detail. We group the tephra horizons into three packages: the older, smaller Tablelands and Paerata tephras; the overlying Kohioawa tephras (correlated with Whakamaru group eruptions); and the younger Murupara and Bonisch tephras. Major- and trace-element compositions suggest these tephras represent six distinct high-silica magma types, with the Kohioawa tephras representing three distinct magma compositions that are atypical of the TVZ. The distribution of Kohioawa magma types (types A, B, and C) changes through time, with the oldest deposits containing exclusively type A magma, the middle deposits containing types A and B, and the youngest deposits containing all three Kohioawa types. A combination of horizon-scale mineralogy and rhyolite-MELTS modeling suggests that only Kohioawa types B and C are saturated in sanidine – the presence of sanidine is atypical in Taupō Volcanic Zone magmas but has been previously documented in the Whakamaru group ignimbrites. Rhyolite-MELTS geobarometry reveals shallow storage pressures (∼50–150 MPa) for Kohioawa magmas. At least three different melt-dominated magma bodies sourced the Kohioawa tephras – these magma bodies were laterally juxtaposed and co-erupted for most of the Whakamaru eruptions. Magmas that preceded and post-dated the Whakamaru eruptions have more typical TVZ compositions, emphasizing the unique features of the Whakamaru system. • Pyroclastic fall deposits are correlated to the Whakamaru group eruptions using tephra deposits ∼90 km from the caldera • Three magma bodies, distinguished by glass chemistry and presence/absence of sanidine, sourced the Whakamaru group eruptions. • Modeled storage depths revealshallow, upper crustal magma bodies sourced the Whakamaru group eruptions (50–150 MPa; ∼ 2–6 km) • Different magma bodies were involved at different times during the eruption(s) [ABSTRACT FROM AUTHOR]

The Puketerata Volcanic Complex formed as a result of a series of rhyolitic eruptions along a 2.5 km long NE-trending eruptive fissure at the southern margin of Maroa Volcanic Centre (Whakamaru caldera) at 16.5 ka. Initial deep-seated explosions were excavated and widen the pre-existing volcanic structures associated to earlier basaltic activity. The following emplacement of two lava domes and associated shallow-seated phreatomagmatic activity produced a widespread tephra blanket characterized by alternating surge and fall dominated pyroclastic units. The silicic magma (73% SiO 2) erupted during the Puketerata activity was highly degassed, where explosive fragmentation was driven only by the interaction with external water. The lava domes and ejecta ring makes up more than two-thirds (98 × 106 m3 DRE) of the total eruptive volume (~ 143 × 106 m3 DRE). The compound ring structures surrounding the larger dome totally overlap the underlying volcanic landforms that formed during the initial phase. The ejecta ring around the larger dome represents a complex landform, which predominantly consists of outwardly thinning pyroclastic breccias forming fan-shape bodies relating to the series of destruction of the larger dome. Despite the relatively large combined dispersal area of the pyroclastic deposits generated by the entire activity (235 km2), the volume of single fall beds do not suggest individual explosive events exceeded VEI 2–3. The volcanic hazards associated with such small-volume volcanoes are largely ignored despite these eruptions being more frequent than eruption characterized by caldera collapses. The example of Puketerata suggests that small-volume volcanism often exhibits activity producing fissures, whereas the varied advancement of dykes influenced by external factors makes the course of the eruptions unpredictable in terms of geometry of vents and eruption styles. Image 1 • A silicic fissure eruption related maar-tuff ring–lava dome complex was examined. • The ~ 100 °C increase of crystallization temperature at the onset of eruption relates to the invasion of basaltic magma. • Eruption styles were controlled by the availability of groundwater and the quenching process of degassed rhyolitic magma. • A breccia-dominated steep ejecta ring was formed around the larger lava dome. • The inferred maximum 4–5 m3/s eruption rate indicates the prolonged nature of such volcanic events. [ABSTRACT FROM AUTHOR]

The thermal structures of eruption-fed, subglacial volcaniclastic deposits are poorly understood because their emplacement is hazardous to observe or obscured by the glacier. Determining deposit emplacement temperature, however, supports improved understanding of the flow dynamics and emplacement processes of volcaniclastic material beneath a glacier. Understanding the emplacement temperatures of ancient volcanic deposits is also important because they can be used, in combination with field studies, to infer the eruptive environment. Here, we use paleomagnetic techniques to quantify the emplacement temperatures of two ancient, proximal, eruption-fed density current deposits at Tongariro volcano, New Zealand. Stepwise thermal demagnetisation of lithic and recycled juvenile block-sized clasts reveal randomly orientated directions of magnetisation, suggesting that the clasts were rotated within the flow but not heated. Additional data from thermomagnetic, hysteresis, and isothermal remanent magnetisation tests indicate that the principal carrier of magnetic remanence is magnetite, and that the magnetisation directions are a primary remanence rather than post-depositional chemical remanent magnetisations. Following systematic removal of any viscous remanent magnetisation, the post-emplacement equilibrium temperatures for the deposits can be estimated at <150 °C. The paleomagnetic data support field evidence for rapid cooling of clasts and waterlain deposition. The deposit-forming eruptions took place beneath a summit glacier where the freshly erupted tephra was efficiently cooled by mixing with meltwater. Lithic blocks and recycled juvenile bombs were entrained and remobilised within the cool currents that drained along meltwater channels beneath the ice. This is the first study in which paleomagnetic data have been used to determine the equilibrium temperatures of subglacial density current deposits. The data provide new insight into volcaniclastic flow dynamics beneath a glacier and current-meltwater interactions. • Eruption-fed, volcaniclastic flow deposits emplaced at <150 °C. • Magnetic stability tests rule out chemical remanence magnetisation. • Deposition from tephra-laden meltwater currents that drained beneath a glacier. • First use of paleomagnetic techniques for glaciovolcanic deposits. [ABSTRACT FROM AUTHOR]

• We present a new method to determine pressures of extraction of eruptible magma. • Eruptible magma can be stored shallower than the level of extraction. • In the Taupo Volcanic Zone flare-up, extraction and storage evolve through time. • Our method can be used to probe the architecture of ancient magmatic systems. The deposits of large volcanic eruptions provide the sole record of the architecture of magmatic plumbing systems in the moments when large pools of crystal-poor, eruptible magma are present in the crust. It is widely accepted that silicic magmas form by segregation of melt-rich, crystal-poor magma from a crystal-rich source; however, the depths at which segregation takes place and the distribution of the magma within the crust are not well constrained. We present a new approach to calculate pressures at which crystal-poor, eruptible magma is extracted from a crystal-rich source (i.e. mush). We apply the approach to a sequence of large (>50 km3) eruptions from the Taupo Volcanic Zone (TVZ), New Zealand, which were part of a volcanic flare-up. We compare the calculated extraction pressures with pre-eruptive storage pressures for the same units. Our results show that storage and extraction pressures do not always coincide. Instead, eruptible magma can be completely segregated from the crystal-rich source, and stored at shallower levels in the crust prior to eruption. In the case of the TVZ flare-up, repeated input of material and heat – probably coupled with tectonic extension – gradually conditioned the crust and allowed extraction of eruptible magma over a growing range of pressures with time. Our approach has the potential to reveal important information on the structure and distribution of magmatic systems within the shallow crust. [ABSTRACT FROM AUTHOR]