Auckland, New Zealand, is home to 1.4 million people, over a third of New Zealand's population, and accounts for ∼35% of New Zealand's GDP (Statistics New Zealand, 2014). The city is built on top of the Auckland Volcanic Field (AVF), which covers 360 km2, has over 50 eruptive centres (vents), and has erupted over 55 times in the past 250,000 years, producing a cumulative volume of ∼2 km3 of tephra, lava and other volcanic deposits1 (see Figure 5.1). The field is likely to erupt again: the most recent eruption, Rangitoto, was only 550 years ago. Most AVF vents are monogenetic, i.e. they only erupt once. This means that it is very likely that the next vent will erupt in a new location within the field. Despite considerable scientific efforts, no spatial (where) or temporal (when) patterns have been identified; indeed, the oldest (Pupuke volcano) and the youngest (Rangitoto) vents are located next to each other. As such, it is wholly unknown where or when the next eruption will be. The size of the next eruption is also difficult to address, as the last eruption, Rangitoto, accounts for nearly half of the erupted volume of the field, and it is unclear whether this eruption is an anomaly or signals a change in the eruptive behaviour of the field. These difficulties of assessing location, time and size of next eruption pose a considerable problem for emergency and risk managers. The main challenges facing Auckland and other populated areas coinciding with volcanic fields include:
Abstract Lava flows can cause substantial physical damage to elements of the built environment. Often, lava flow impacts are assumed to be binary, i.e. cause complete damage if the lava flow and asset are in contact, or no damage if there is no direct contact. According to this paradigm, buried infrastructure would not be expected to sustain damage if a lava flow traverses the ground above. However, infrastructure managers (“stakeholders”) have expressed concern about potential lava flow damage to such assets. We present a workflow to assess the thermal hazard posed by lava flows to buried infrastructure. This workflow can be applied in a pre-defined scenario. The first step in this workflow is to select an appropriate lava flow model(s) and simulate the lava flow’s dimensions, or to measure an in situ lava flow’s dimensions. Next, stakeholders and the modellers collaborate to identify where the lava flow traverses buried network(s) of interest as well as the thermal operating conditions of these networks. Alternatively, instead of direct collaboration, this step could be done by overlaying the flow’s areal footprint on local infrastructure maps, and finding standard and maximum thermal operating conditions in the literature. After, the temperature of the lava flow at the intersection point(s) is modelled or extracted from the results of the first step. Fourth, the lava flow-substrate heat transfer is calculated. Finally, the heat transfer results are simplified based on the pre-identified thermal operating conditions. We illustrate how this workflow can be applied in an Auckland Volcanic Field (New Zealand) case study. Our case study demonstrates considerable heat is transferred from the hypothetical lava flow into the ground and that maximum operating temperatures for electric cables are exceeded within 1 week of the lava flow front’s arrival at the location of interest. An exceedance of maximum operating temperatures suggests that lava flows could cause thermal damage to buried infrastructure, although mitigation measures may be possible.
Abstract Harrat Rahat (<10 Ma) is one of the largest volcanic fields on western Arabia. In the north of the field, some of the youngest volcanic centres evolved through either point-like, complex or multiple aligned vents (i.e. along fissures), and have pyroclastic cones, lapilli fall deposits and/or lava flows associated with them. The products reflect dominantly Hawaiian eruptions, and only one centre experienced phreatomagmatism. Results from new 3 He surface-exposure dating provide constraints on stratigraphy of the youngest (<0.3 Ma) products. The rocks are compositionally alkali-basalt and hawaiite, with intra-plate basalt (prevalent mantle (PREMA)) affinity. Each eruption displays a distinct whole-rock composition in an overall linear trend. We suggest that the magma source for each centre is similar, and that composition of the products is different due to different degrees of fractionation. In a single eruption, the magma that reaches the surface first is the least evolved, with the most evolved magma erupting last. We also found that the most primitive magmas erupt less explosively. We think that the degree of magma evolution might correlate with ascent times, assuming that the more evolved magma spent more time en route. We suggest that magma ascent time is likely to be longer than that of other more primitive intra-plate basalts. Supplementary material: Whole-rock chemistry results, mineral chemistry results and fractional crystallization modeling data are available at https://doi.org/10.6084/m9.figshare.c.3488988
Glass inclusions in plagioclase and orthopyroxene from dacitic pumice of the Cabrits Dome, Plat Pays Volcanic Complex in southern Dominica reveal a complexity of element behavior and Li–B isotope variations in a single volcanic center that would go unnoticed in a whole-rock study. Inclusions and matrix glasses are high-silica rhyolite with compositions consistent with about 50% fractional crystallization of the observed phenocrysts. Estimated crystallization conditions are 760–880°C, 200 MPa and oxygen fugacity of FMQ + 1 to +2 log units (where FMQ is the fayalite–magnetite–quartz buffer). Many inclusion glasses are volatile-rich (up to 6 wt % H2O and 2900 ppm Cl), but contents range down to 1 wt % H2O and 2000 ppm Cl as a result of shallow-level degassing. Sulfur contents are low throughout, with <350 ppm S. The trace element composition of inclusion glasses shows enrichment in light rare earth elements (LREE; (La/Sm)n = 2·5–6·6) and elevated Ba, Th and K contents compared with whole rocks and similar or lower Nb and heavy REE (HREE; (Gd/Yb)n = 0·5–1·0). Lithium and boron concentrations and isotope ratios in melt inclusions are highly variable (20–60 ppm Li with δ7Li = +4 to +15 ± 2‰; 60–100 ppm B with δ11B = +6 to +13 ± 2‰) and imply trapping of isotopically heterogeneous, hybrid melts. Multiple sources and processes are required to explain these features. The mid-ocean ridge basalt (MORB)-like HREE, Nb and Y signature reflects the parental magma(s) derived from the mantle wedge. Positive Ba/Nb, B/Nb and Th/Nb correlations in inclusion glasses indicate coupled enrichment in strongly fluid-mobile (Ba, B) and less-mobile (Th, Nb) trace elements, which can be explained by fractional crystallization of plagioclase, orthopyroxene and Fe–Ti oxides. The δ7Li and δ11B values are at the high end of known ranges for other island arc magmas. We attribute the high values to a 11B and 7Li-enriched slab component derived from sea-floor-altered oceanic crust and possibly further enriched in heavy isotopes by dehydration fractionation. The heterogeneity of isotope ratios in the evolved, trapped melts is attributed to shallow-level assimilation of older volcanic rocks of the Plat Pays Volcanic Complex.
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