Ash Generation in the 2012 Eruption of Havre Volcano, Kermadec Arc: The Largest Deep Subaqueous Eruption of the Last Century

The 2012 silicic eruption at Havre volcano, in the Kermadec Arc, was the largest deep subaqueous eruption observed in the last century. A data set of unprecedented richness was collected during a dedicated research cruise in 2015, including detailed bathymetric mapping and systematic in situ sampling of seafloor clastic and effusive products. This thesis characterizes the seafloor Ash and Lapilli (AL) Unit produced during the 2012 Havre eruption, with the aim of determining the effect of the water column on ascent, fragmentation, and dispersal of ash during a deep silicic subaqueous eruption. To this end, sample grain-size distributions, sample componentry, ash shape and microtextural data, major-element chemistry, and groundmass volatile contents were acquired. Results and interpretations from the AL Unit support inferences on eruption processes. It is demonstrated that the AL Unit is a composite deposit composed of four subunits; from base to top these are Subunit 1 (S1), 2 (S2), 3 (S3), 4a and 4b (S4). Each of the subunits in the AL Unit shows distinctive grain size or componentry characteristics, different mapped dispersal limits, and specific stratigraphic relationship with the other seafloor products of the 2012 Havre eruption. Using results of subunit depositional characteristics and particle microtextural features mechanisms are inferred to explain the generation of each subunits of the AL Unit. Subunit 1 directly overlies the Giant Pumice Unit, draping the entire study area and fining towards the NW. This deposit is composed of an average 125 to 800 µm glassy vesicular ash showing dominantly curvi-planar morphologies, in addition to lesser amounts of angular and fluidal particles. Subunit 1 is therefore inferred to have been deposited by fallout following dispersal in an eruptive plume. The plume was driven by an eruption defined by energetic fragmentation with a large component of magma water interaction, however also apparently showing a range of other fragmentation processes. Subunit 2 overlying S1 across a gradational contact shows a deposit boundary along the northern caldera wall. To the south of the boundary S2 is heavily thickened in the caldera showing a consistent grain size. Subunit 2 is composed of 16 to 32 µm glassy vesicular ash showing dominantly curvi-planar morphologies, in addition to lesser amounts of angular and fluidal particles. This subunit is inferred to have been deposited from dilute density currents that ponded in the Havre caldera. The similarity in microtextural features to S1 and their gradational contact suggest these two subunits were generated from the same event. With density currents potentially generated off a larger eruption column. The microtextural similarity of these deposits to the GP Unit and ALB Unit suggests their eruption from the dome OP vent, while the presence of fluidal particles and energetic fragmentation indicates and explosive eruption. Subunit 3 drapes topography in a NE-SW trend across the caldera thinning and fining towards a lava flow on the southern caldera rim. The morphological and microtextural similarity of the ash the S3 is composed of to the pumaceous carapace of the said lava suggests this was its source. By modelling the thermal plume required to generated S3 however it is shown that weakly pyroclastic activity is required to produce the wide dispersal, likely occurring synchronously with lava effusion. Subunit 4 is composed of microcrystalline ash, the low vesicularity and high crystallinity of which suggests fragmentation from the lava flows. Subunit 4a dispersed in a NE-SW trend across the caldera is inferred to have been generated during a caldera wall collapse near the source vents of 3 lavas produced during the 2012 eruption. Subunit 4b dispersed around Dome OP in inferred to have been generated by quenching and brecciation of the lava as it was extruded. The results presented in this thesis show that the 2012 deep subaqueous eruption of Havre volcano was a complex event, with both explosive and effusive activity occurring over several phases. The eruptive processes were significantly influenced by the water column, which affected magma rheology, magma fragmentation to produce fine ash, initial particle dispersal, and final deposition

Characteristics and Deposit Stratigraphy of Submarine-Erupted Silicic Ash, Havre Volcano, Kermadec Arc, New Zealand

Submarine eruptions dominate volcanism on Earth, but few are observed or even identified. Knowledge of how they operate is largely based on inference from ancient deposits, lagging by a decade or more our understanding of subaerial eruptions. In 2012, the largest wholly deep-subaqueous silicic eruption with any observational record occurred 700–1220 m below sea level at Havre volcano, Kermadec Arc, New Zealand. Pre- and post-eruption shipboard bathymetry surveys, acquisition by autonomous underwater vehicle of meter-scale-resolution bathymetry, and sampling by remote-operated vehicle revealed 14 seafloor lavas and three major seafloor clastic deposits. Here we analyze one of these clastic deposits, an Ash with Lapilli (AL) unit, which drapes the Havre caldera, and interpret the fragmentation and dispersal processes that produced it. Seafloor images of the unit reveal multiple subunits, all ash-dominated. Sampling destroyed layering in all but two samples, but by combining seafloor imagery with granulometry and componentry, we were able to determine the subunits’ stratigraphy and spatial extents throughout the study area. Five subunits are distinguished; from the base these are Subunit 1, Subunit 2a, Subunit 3, Subunit 4 (comprising the coeval Subunit 4 west and Subunit 4 east), and Subunit 2b. The stratigraphic relationships of the four AL unit subunits to other seafloor products of the 2012 Havre eruption, coupled with the wealth of remote-operated vehicle observations and detailed AUV bathymetry, allow us to infer the overall order of events through the eruption. Ash formed by explosive fragmentation of a glassy vesicular magma and was dispersed by a buoyant thermal plume and dilute density currents from which Subunits 1 and 2 were deposited. Following a time break (days/weeks?), effusion of lava along the southern caldera rim led to additional ash generation; first by syn-extrusive ash venting, quenching, brecciation, and comminution (S3 and S4e) and then by gravitational collapse of a dome (S4w). Slow deposition of extremely fine ash sustained S2 deposition across the times of S3 and S4 emplacement, so that S2 ash was the last deposited. These thin ash deposits hold information critical for interpretation of the overall eruption, even though they are small in volume and bathymetrically unimpressive. Ash deposits formed during other submarine eruptions are similarly likely to offer new perspectives on associated lavas and coarse pumice beds, both modern and ancient, and on the eruptions that formed them. Submarine ash is widely dispersed prior to deposition, and tuff is likely to be the first product of eruption identified in reconnaissance exploration; it is the start of the trail to vent hydrothermal systems and associated mineralized deposits of submarine volcanoes, as well as a sensitive indicator of submarine eruptive processes

PARTIcle Shape ANalyzer PARTISAN – an open source tool for multi-standard two-dimensional particle morphometry analysis

In volcanology, 2D morphometric analysis is a method often applied for quantitative characterization of eruptive products, used to compare tephra from different events or phases, infer eruptive styles and underlying clast generating mechanisms, or describe the aerodynamic behavior of tephra. Such particle shape analyses can be conducted using particle silhouettes or cross-sectional slices, obtained under by means of electron or optical microscope imagery. Over the course of the last years, a number of different morphometric systems have been used. Each of them uses its own nomenclature and mathematical definitions of shape-describing parameters, some of which can only be obtained using specific commercial software. With the PARTIcal Shape ANalyzer PARTISAN we present a freeware tool which parameterizes 2D shapes and provides a suite of shape descriptors, following the respective standards of the five most commonly used 2D morphometric systems. Use of PARTISAN will enable the user to study and archive the results of particle shape analysis in a format compatible with various published routines, thus increasing the potential for linking new work with results of work previously published by other groups. It will allow as well the cross-comparison of results obtained by these morphological routines. PARTISAN hence could be seen as a "Rosetta Stone" for volcanological particle morphometry, and opens the way towards an inter-group effort for a standardized 2D description of particle shapes

The largest deep-ocean silicic volcanic eruption of the past century

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 4 (2018): e1701121, doi:10.1126/sciadv.1701121.The 2012 submarine eruption of Havre volcano in the Kermadec arc, New Zealand, is the largest deep-ocean eruption in history and one of very few recorded submarine eruptions involving rhyolite magma. It was recognized from a gigantic 400-km2 pumice raft seen in satellite imagery, but the complexity of this event was concealed beneath the sea surface. Mapping, observations, and sampling by submersibles have provided an exceptionally high fidelity record of the seafloor products, which included lava sourced from 14 vents at water depths of 900 to 1220 m, and fragmental deposits including giant pumice clasts up to 9 m in diameter. Most (>75%) of the total erupted volume was partitioned into the pumice raft and transported far from the volcano. The geological record on submarine volcanic edifices in volcanic arcs does not faithfully archive eruption size or magma production.This research was funded by Australian Research Council Postdoctoral fellowships (DP110102196 and DE150101190 to R. Carey), a short-term postdoctoral fellowship grant from the Japan Society for the Promotion of Science (to R. Carey), National Science Foundation grants (OCE1357443 to B.H., OCE1357216 to S.A.S., and EAR1447559 to J.D.L.W.), and a New Zealand Marsden grant (U001616 to J.D.L.W.). J.D.L.W. and A.M. were supported by a research grant and PhD scholarship from the University of Otago. R.W. was supported by NIWA grant COPR1802. J.D.L.W. and F.C.-T. were supported by GNS Science grants CSA-GHZ and CSA-EEZ. M.J. was supported by the U.S. Department of Defense (DoD) through the National Defense Science and Engineering Graduate Fellowship (NDSEG) Program

Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

Ash Generation in the 2012 Eruption of Havre Volcano, Kermadec Arc: The Largest Deep Subaqueous Eruption of the Last Century

The 2012 silicic eruption at Havre volcano, in the Kermadec Arc, was the largest deep subaqueous eruption observed in the last century. A data set of unprecedented richness was collected during a dedicated research cruise in 2015, including detailed bathymetric mapping and systematic in situ sampling of seafloor clastic and effusive products. This thesis characterizes the seafloor Ash and Lapilli (AL) Unit produced during the 2012 Havre eruption, with the aim of determining the effect of the water column on ascent, fragmentation, and dispersal of ash during a deep silicic subaqueous eruption. To this end, sample grain-size distributions, sample componentry, ash shape and microtextural data, major-element chemistry, and groundmass volatile contents were acquired. Results and interpretations from the AL Unit support inferences on eruption processes. It is demonstrated that the AL Unit is a composite deposit composed of four subunits; from base to top these are Subunit 1 (S1), 2 (S2), 3 (S3), 4a and 4b (S4). Each of the subunits in the AL Unit shows distinctive grain size or componentry characteristics, different mapped dispersal limits, and specific stratigraphic relationship with the other seafloor products of the 2012 Havre eruption. Using results of subunit depositional characteristics and particle microtextural features mechanisms are inferred to explain the generation of each subunits of the AL Unit. Subunit 1 directly overlies the Giant Pumice Unit, draping the entire study area and fining towards the NW. This deposit is composed of an average 125 to 800 µm glassy vesicular ash showing dominantly curvi-planar morphologies, in addition to lesser amounts of angular and fluidal particles. Subunit 1 is therefore inferred to have been deposited by fallout following dispersal in an eruptive plume. The plume was driven by an eruption defined by energetic fragmentation with a large component of magma water interaction, however also apparently showing a range of other fragmentation processes. Subunit 2 overlying S1 across a gradational contact shows a deposit boundary along the northern caldera wall. To the south of the boundary S2 is heavily thickened in the caldera showing a consistent grain size. Subunit 2 is composed of 16 to 32 µm glassy vesicular ash showing dominantly curvi-planar morphologies, in addition to lesser amounts of angular and fluidal particles. This subunit is inferred to have been deposited from dilute density currents that ponded in the Havre caldera. The similarity in microtextural features to S1 and their gradational contact suggest these two subunits were generated from the same event. With density currents potentially generated off a larger eruption column. The microtextural similarity of these deposits to the GP Unit and ALB Unit suggests their eruption from the dome OP vent, while the presence of fluidal particles and energetic fragmentation indicates and explosive eruption. Subunit 3 drapes topography in a NE-SW trend across the caldera thinning and fining towards a lava flow on the southern caldera rim. The morphological and microtextural similarity of the ash the S3 is composed of to the pumaceous carapace of the said lava suggests this was its source. By modelling the thermal plume required to generated S3 however it is shown that weakly pyroclastic activity is required to produce the wide dispersal, likely occurring synchronously with lava effusion. Subunit 4 is composed of microcrystalline ash, the low vesicularity and high crystallinity of which suggests fragmentation from the lava flows. Subunit 4a dispersed in a NE-SW trend across the caldera is inferred to have been generated during a caldera wall collapse near the source vents of 3 lavas produced during the 2012 eruption. Subunit 4b dispersed around Dome OP in inferred to have been generated by quenching and brecciation of the lava as it was extruded. The results presented in this thesis show that the 2012 deep subaqueous eruption of Havre volcano was a complex event, with both explosive and effusive activity occurring over several phases. The eruptive processes were significantly influenced by the water column, which affected magma rheology, magma fragmentation to produce fine ash, initial particle dispersal, and final deposition

Fragmentation experiments with Havre melt: dry and induced fuel-coolant interaction runs

Here we present the data records (raw data) from 19 fragmentation experiments. In these runs silicic HVR254 dome rock (retrieved from the submarine Havre volcano) was crushed, remelted and fragmented using two different experimental settings: 1. dry runs (records labelled "D"): melt was fragmented by injection of pressurized Ar gas. 2. induced fuel-coolant interaction runs (records labelled "IFCI"): a water layer was established on top of the melt, before gas was injected from below. This caused fragmentation of the melt plug under IFCI conditions. Note that the runs D07, D08, D09, IFCI08 and IFCI09 used a reduced melt mass (100g instead of 250g). Files contain (separated by column) records of: time, trigger signal, force, pressure, microphone, electric field, seismic data. The units and amplification settings used are provided in the file headers. In addition, the results of morphometry analysis (t-tests) are provided in a pdf file. The morphometric analyses of natural ash focused exclusively on the curvi-planar grains dominant in Havre ash samples, labelled "Nat1" - "Nat6". Four types of experimental grains were compared with them: • “DG”: particles from dry runs, from the lab floor • “IG”: grains from open IFCI runs, from the lab floor • “IW”: very small particles from open IFCI runs deposited in water droplets on the walls and ceiling around the experimental area • “IU”: particles from IFCI runs with U-tube, from the water bow

The largest deep-ocean silicic volcanic eruption of the past century.

The 2012 submarine eruption of Havre volcano in the Kermadec arc, New Zealand, is the largest deep-ocean eruption in history and one of very few recorded submarine eruptions involving rhyolite magma. It was recognized from a gigantic 400-km2 pumice raft seen in satellite imagery, but the complexity of this event was concealed beneath the sea surface. Mapping, observations, and sampling by submersibles have provided an exceptionally high fidelity record of the seafloor products, which included lava sourced from 14 vents at water depths of 900 to 1220 m, and fragmental deposits including giant pumice clasts up to 9 m in diameter. Most (>75%) of the total erupted volume was partitioned into the pumice raft and transported far from the volcano. The geological record on submarine volcanic edifices in volcanic arcs does not faithfully archive eruption size or magma production