Browsing by Author "Leonard GS"

Now showing 1 - 3 of 3
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    Ruapehu and Tongariro stratovolcanoes: a review of current understanding
    (Taylor and Francis Group on behalf of GNS Science Ltd, 2021-05-02) Leonard GS; Cole RP; Christenson BW; Conway CE; Cronin SJ; Gamble JA; Hurst T; Kennedy BM; Miller CA; Procter JN; Pure LR; Townsend DB; White JDL; Wilson CJN
    Ruapehu (150 km3 cone, 150 km3 ring-plain) and Tongariro (90 km3 cone, 60 km3 ring-plain) are iconic stratovolcanoes, formed since ∼230 and ∼350 ka, respectively, in the southern Taupo Volcanic Zone and Taupo Rift. These volcanoes rest on Mesozoic metasedimentary basement with local intervening Miocene sediments. Both volcanoes have complex growth histories, closely linked to the presence or absence of glacial ice that controlled the distribution and preservation of lavas. Ruapehu cone-building vents are focused into a short NNE-separated pair, whereas Tongariro vents are more widely distributed along that trend, the differences reflecting local rifting rates and faulting intensities. Both volcanoes have erupted basaltic andesite to dacite (53–66 wt.% silica), but mostly plagioclase-two pyroxene andesites from storage zones at 5–10 km depth. Erupted compositions contain evidence for magma mixing and interaction with basement rocks. Each volcano has an independent magmatic system and a growth history related to long-term (>104 years) cycles of mantle-derived magma supply, unrelated to glacial/interglacial cycles. Historic eruptions at both volcanoes are compositionally diverse, reflecting small, dispersed magma sources. Both volcanoes often show signs of volcanic unrest and have erupted with a wide range of styles and associated hazards, most recently in 2007 (Ruapehu) and 2012 (Tongariro).
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    Tsunami awareness and preparedness in Aotearoa New Zealand: The evolution of community understanding
    (Elsevier Ltd, 2021-11-01) Dhellemmes A; Leonard GS; Johnston DM; Vinnell LJ; Becker JS; Fraser SA; Paton D
    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.
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    Volcanic ballistic projectile deposition from a continuously erupting volcano: Yasur Volcano, Vanuatu
    (Presses universitaires de Strasbourg, 2020-08-25) Fitzgerald RH; Kennedy BM; Gomez C; Wilson TM; Simons B; Leonard GS; Matoza RS; Jolly AD; Garaebiti E
    Volcanic Ballistic Projectiles (VBPs) are the main hazard to life and infrastructure from Strombolian eruptions. This eruption style is a tourist drawcard, exposing people to VBP hazard. Most of the research on VBPs to date has been focussed on understanding how they form and their trajectory. However, little focus has been placed on how they are spatially distributed within VBP fields or the inclusion of these data into hazard and risk assessments. In this study, we used a drone to image the east and south flanks of Yasur Volcano, Vanuatu, and cameras, infrasound, and seismicity to record explosions from 28 July to 2 August and 17 to 19 October 2016. We present the mapped spatial distribution of VBPs from the two trips, assessing how the VBP field changes with distance and direction from the vent, and how eruption dynamics influence these changes. We found that the VBP spatial density and median diameter decrease with distance from the crater. Spatial density was also found to vary with direction around the crater, with higher spatial densities found in the S-SSE than other directions. Combined with observations of explosions, we attribute the changes in spatial density to explosion directionality. Our evidence for directionality results in considerable variation in summit VBP hazard and is an important, but by no means the sole, consideration for VBP hazard and risk assessments.