The evolution of Maroa Volcanic Centre, Taupo Volcanic Zone, New Zealand

Maroa Volcanic Centre (Maroa) is located within the older Whakamaru caldera, central Taupo Volcanic Zone, New Zealand. Dome lavas make up the majority of Maroa volume, with the large Maroa West and East Complexes (MWC and MEC, respectively) erupted mostly over a short 29 kyr period starting at 251 ± 17 ka. The five mappable Maroa pyroclastics deposits are discussed in detail. The Korotai (283 ± 11 ka), Atiamuri (229 ±12 ka), and Pukeahua (~229 -196 ka) pyroclastics are all s 1 km3 and erupted from (a) northern Maroa, (b) a vent below Mandarin Dome and (c) Pukeahua Dome Complex vents, respectively. The Putauaki (272 ± 10 ka) and Orakonui (256 ± 12 ka) pyroclastics total ~ 4 km3 from a petrologically and geographically very similar central Maroa source. The ~ 220 ka Mokai pyroclastics outcrop partly within Maroa but their source remains unclear, whereas the ~ 240 ka Ohakuri pyroclastics appear to have come from a caldera just north of Maroa. The ages of the Mamaku, Ohakuri and Mokai pyroclastics are equivocaL The Mamaku and Ohakuri pyroclastics appear to be older (~ 240 ka) than the age previously accepted for the Mamaku pyroclastics. Maroa lavas are all plagioclase-orthopyroxene bearing, commonly with lesser quartz. Hornblende +/- biotite are sometimes present and their presence is correlated with geochemical variation. All Maroa deposits are rhyolites (apart from two high-silica dacite analyses) and are peraluminous and calcic. They all have the trace element signatures of arc-related rocks typical of TVZ deposits. Maroa deposits fall geochemically into three magma types based on Rb and Sr content: M (Rb 80-123 ppm, Sr 65-88 ppm), T (Rb 80-113 ppm, Sr 100-175 ppm) and N (Rb 120-150 ppm, Sr 35- 100 ppm). The geochemical distinction of these types is also seen in the concentrations of most other elements. Based on the spatial, chronological and petrological similarities of the MWC/MEC and Pukeahua eastern magma associations (termed (1) and (2)) a further four magma associations are determined ((3) through (6)). These six associations account for almost all Maroa deposits. Two end-member models are proposed for the sources of each of the Maroa magma associations: (a) a single relatively shallow magma source feeding spatially clustered eruptions, and (b) a deeper source feeding multiple shallower offshoots over a wider area. Sources for the Maroa magma associations probably lie on a continuum between these two model end members. The distinction between Maroa and Taupo Volcanic Centres is somewhat arbitrary and is best considered to be the easting directly north of Ben Lomond, north of which most volcanism is older than 100 ka and M and N type, and south of which most volcanism is younger than 100 ka and T type. The remaining boundaries (north to include Ngautuku, west to include Mokauteure and east to include Whakapapa domes) are arbitrary, and include the farthest domes linked closely, spatially and magmatic ally, to the other Maroa domes. From 230 to 64 ka there was a hiatus in caldera-forming ignimbrite eruptions. Maroa and the Western Dome Belt (WDB) constitute the largest concentrated volume of eruptions (as relatively gentle lava extrusion) during this period. The rate of Maroa volcanism has decreased exponentially from a maximum prior to 200 ka. In contrast volcanism at Taupo and Okataina has increased from ~ 64 ka to present. The oldest Maroa dome (305 ± 17 ka) constrains the maximum rate of infilling of Whakamaru caldera as 39-17 km3/kyr. This highlights the extraordinarily fast rate of infilling common at silicic calderas and is in agreement with international case studies, except where post-collapse structural resurgence has continued for more than 100 kyr. The majority of caldera fill, representing voluminous eruption deposits in the first tens of thousands of years post collapse, is buried and only accessible via drilling. The WDB and Maroa are petrologically distinct from one another in terms of some or all of Rb, Sr, Ba and Zr content, despite eruption over a similar period. Magma sources for Maroa and the WDB may have been partly or wholly derived from the Whakamaru caldera magma system(s), but petrological distinctions among all three mean that Maroa and the WDB cannot be considered as simple magmatic resurgence of the Whakamaru caldera. Maroa's distinct Thorpe Rd Fault is in fact a fossil feature which hasn't been active in almost 200 kyr. In addition, the graben across Tuahu Dome was likely created by shallow blind diking. Several recent studies across TVZ show structural features with some associated dike intrusion/eruption. Such volcano tectonic interaction is rarely highlighted in TVZ but may be relatively common and lie on a continuum between dike-induced faulting and dikes following structural features. Although rates of volcanism are now low in Maroa magmatic intrusion appears to remain high. This raises the possibility of a causative link between faulting and volcanism in contrast to traditional views of volcanism controlled by rates of magmatic ascent. Probable future eruptions from Maroa are likely to be of similar scale (<0.1 km3 ) and frequency (every ~ 14,000 years) to most of those over the last 100 ka. Several towns lie in a range of zones of Maroa volcanic hazard from total destruction to possible ash fall. However, the probability of a future eruption is only ~ 0.6 % in an 80 year lifetime

Os isotopic constraints on crustal contamination in Auckland Volcanic Field basalts, New Zealand

The Auckland Volcanic Field (AVF) represents the youngest and northernmost of three subjacent Quaternary intraplate basaltic volcanic fields in the North Island, New Zealand. Previous studies on AVF eruptive products suggested that their major- and trace-element, and Sr-, Nd- and Pb-isotopic signatures primarily reflect their derivation from the underlying asthenospheric and lithospheric mantle. All AVF lavas however ascend through a ca. 20–30 km thick continental crust, and some do carry crustal xenoliths, posing the question whether or not crustal contamination plays a role in their formation. Here we present new Os and Pb isotopic data, and Os and Re concentrations for 15 rock samples from 7 AVF volcanic centres to investigate mantle and crustal petrogenetic processes. The samples include the most primitive lavas from the field (Mg# 59–69) and span a range of eruption sizes, ages, locations, and geochemical signatures. The data show a large range in Os concentrations (6–579 ppt) and 187Os/188Os isotope ratios from mantle-like (0.123) to highly radiogenic (0.547). Highly radiogenic Os signatures together with relatively low Os contents in most samples suggest that ascending melts experienced contamination primarily from metasedimentary crustal rocks with high 187Os/188Os ratios (e.g., greywacke). We further demonstrate that < 1% metasedimentary crustal input into the ascending melt can produce the radiogenic Os isotope signatures observed in the AVF data. This low level of crustal contamination has no measurable effect on the corresponding trace element ratios and Sr-Nd-Pb isotopic compositions. In addition, high Os contents (195–578 ppt) at slightly elevated but mantle-like Os isotopic compositions (187Os/188Os = 0.1374–0.1377) in some samples suggest accumulation of xenocrystic olivine-hosted mantle sulphides from the Permian-Triassic ultramafic Dun Mountain Ophiolite Belt, which traverses the crust beneath the Auckland Volcanic Field. We therefore infer that the AVF Os isotopic compositions and Os contents reflect contamination from varying proportions of heterogeneous crustal components, composed of Waipapa and Murihiku terrane metasediments, and ultramafic rocks of the Dun Mountain Ophiolite Belt. This demonstrates, contrary to previous models that primitive lavas from the Auckland Volcanic Field do show evidence for variable interaction with the crust

Tsunami awareness and preparedness in Aotearoa New Zealand:The evolution of community understanding

After catastrophic events such as the 2004 Indian Ocean tsunami and the 2011 Great East Japan earthquake and tsunami there is a clear need for vulnerable countries like Aotearoa New Zealand to get prepared for tsunami. In the last ten years, the New Zealand government initiated major efforts to raise awareness of tsunami risk among coastal residents. This study explores tsunami awareness, preparedness, and evacuation intentions among residents of the East Coast of the North Island in a 2015 survey. The ten chosen locations also participated in a tsunami survey in 2003, with results demonstrating that tsunami awareness rose in the twelve years between the surveys. The 2015 survey also included questions on preparedness and intended action. Even though coastal residents know they live in a tsunami prone area, preparedness is relatively low and high expectations of a formal warning remain, even for a local source tsunami scenario. Furthermore, survey respondents had unrealistic ideas of evacuation procedures. When asked about their evacuation intentions, respondents intended to undertake a number of different actions before evacuating their homes, which could cause significant delays in the evacuation process. Most respondents were also reluctant to evacuate on foot and prefer using their vehicles instead, which could create dangerous traffic congestion. These surveyed intentions are consistent with a study of actual evacuation behaviours in the subsequent 2016 Kaikōura earthquake and tsunami, providing validation for the survey indicators. This paper identifies the procedures least understood by the public and offers some solutions to improve tsunami preparedness.</p

The cost-effectiveness of radiofrequency ablation for treating patients with gastric antral vascular ectasia refractory to first line endoscopic therapy

OBJECTIVE: This economic evaluation aims to provide a preliminary assessment of the cost-effectiveness of radiofrequency ablation (RFA) compared with argon plasma coagulation (APC), when used to treat APC-refractory gastric antral vascular ectasia (GAVE) in symptomatic patients.METHODS: A Markov model was constructed to undertake a cost-utility analysis for adults with persistent symptoms secondary to GAVE refractory to first line endoscopic therapy. The economic evaluation was conducted from a UK NHS and personal social services (PSS) perspective, with a 20-year time horizon, comparing RFA with APC. Patients transfer between health states defined by haemoglobin level. The clinical effectiveness data were sourced from expert opinion, resource use and costs were reflective of the UK NHS and benefits were quantified using Quality Adjusted Life Years (QALYs) with utility weights taken from the literature. The primary output was the Incremental Cost-Effectiveness Ratio (ICER), expressed as cost per QALY gained.RESULTS: Over a lifetime time horizon, the base case ICER was £4,840 per QALY gained with an 82.2% chance that RFA was cost-effective at a threshold of £20,000 per QALY gained. The model estimated that implementing RFA would result in reductions in the need for intravenous iron, endoscopic intervention and requirement for blood transfusions by 27.1%, 32.3% and 36.5% respectively. Compared to APC, RFA was associated with an estimated 36.7% fewer procedures.CONCLUSIONS: RFA treatment is likely to be cost-effective for patients with ongoing symptoms following failure of first line therapy with APC and could lead to substantive reductions in health care resource

Tephra clean-up after the 2015 eruption of Calbuco volcano, Chile: A quantitative geospatial assessment in four communities

Reliable methods for volcanic impact and risk assessments are essential. They provide constructive information to emergency and disaster managers, critical infrastructure providers, the insurance industry, and wider society. Posteruption clean-up of tephra deposits is a prevalent and expensive (time and resource) activity which is often not planned for. Here, we present an overview of the clean-up efforts undertaken in four communities after the VEI 4 eruption of Calbuco volcano in 2015. We narratively reconstruct clean-up efforts in Ensenada (Chile), Junín de los Andes (Argentina), San Martín de los Andes (Argentina), and Villa La Angostura (Argentina) using semi-structured interviews, syn- and post-deposition photographs, pre- and post-event visual spectrum satellite imagery, and media reports. We compare these reconstructions with estimates based on a geospatial modelling approach adapted from Hayes et al. (Journal of Applied Volcanology 6:1; 2017). Specifically, we compare reported and geospatially derived estimates for volume of tephra removed, and clean-up operation duration. Our modelling approach performed well for Junín de los Andes but did not adequately capture volume and clean-up operation duration for the three remaining case study locations. We discuss several sources of uncertainty (including observational errors and natural variance of tephra deposit thickness), reported tephra removal volume estimates, clean-up methods, land use, and temporal evolution of clean-up operation demand. Our work demonstrates the utility of using simple geospatial data to develop assessments for tephra clean-up for use in response and recovery planning, and quantitative volcanic impact and risk assessments.Fil: Hayes, Josh. University of Canterbury; Nueva ZelandaFil: Wilson, Thomas M.. University of Canterbury; Nueva ZelandaFil: Stewart, Carol. Massey University Wellington; Nueva ZelandaFil: Villarosa, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; ArgentinaFil: Salgado, Pablo Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales; ArgentinaFil: Beigt, Debora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales; ArgentinaFil: Outes, Ana Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales; ArgentinaFil: Deligne, Natalia I.. GNS Science; Nueva ZelandaFil: Leonard, Graham S.. GNS Science; Nueva Zeland

Aging in One-Dimensional Coagulation-Diffusion Processes and the Fredrickson-Andersen Model

We analyse the aging dynamics of the one-dimensional Fredrickson-Andersen (FA) model in the nonequilibrium regime following a low temperature quench. Relaxation then effectively proceeds via diffusion limited pair coagulation (DLPC) of mobility excitations. By employing a familiar stochastic similarity transformation, we map exact results from the free fermion case of diffusion limited pair annihilation to DLPC. Crucially, we are able to adapt the mapping technique to averages involving multiple time quantities. This relies on knowledge of the explicit form of the evolution operators involved. Exact results are obtained for two-time correlation and response functions in the free fermion DLPC process. The corresponding long-time scaling forms apply to a wider class of DLPC processes, including the FA model. We are thus able to exactly characterise the violations of the fluctuation-dissipation theorem (FDT) in the aging regime of the FA model. We find nontrivial scaling forms for the fluctuation-dissipation ratio (FDR) X = X(tw/t), but with a negative asymptotic value X = -3*pi/(6*pi - 16) = -3.307. While this prevents a thermodynamic interpretation in terms of an effective temperature, it is a direct consequence of probing FDT with observables that couple to activated dynamics. The existence of negative FDRs should therefore be a widespread feature in non mean-field systems.Comment: 39 pages, 4 figure