Mapping and modelling phreatic ballistic fields at tourism hotspots : a methodological assessment at Tongariro and Whakaari (White Island) Volcanoes, New Zealand.

• Main Author: Gates, Stephanie Louise
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury 2018
• Subjects: New Zealand; White Island
• Online Access: http://hdl.handle.net/10092/16177; https://doi.org/10.26021/5694

Ballistic projectiles ejected during explosive volcanic eruptions pose a significant hazard to people, infrastructure, buildings and the environment due to their high impact and sometimes heat energy, accounting for 40% of deaths within 5 km of volcanoes. Phreatic, steam-driven explosive eruptions, which often produce ballistics, are the most common eruption type on earth and can occur without warning. Active volcanoes with geothermal features such as bubbling crater lakes and fumaroles attract tourists, yet are most at risk of erupting phreatically. Recent mass casualties following hydrothermal or phreatic eruptions at Ontake Volcano, Japan in 2014, and a near miss at Tongariro, New Zealand in 2012, have highlighted the hazards posed by ballistics to tourists from relatively small but unheralded explosive eruptions. Ballistic hazard assessments are essential for informing risk management for these unexpected, ballistic-producing eruptions. A ballistic hazard assessment seeks to determine the probability of eruptions which may eject ballistics, and to identify the areas or elements that ballistics may impact. A key part of this assessment is quantifying the area impacted and the intensity of the hazard within it, in metrics such as impact energy or number of blocks per area. However, current ballistic hazard assessments are limited by mapping methods which sample only a small proportion of a ballistic deposit, and guidance for field-appropriate methods is lacking. This thesis aims to advance ballistic hazard assessments by: (1) improving methods for mapping ballistic deposits through a comparative study; (2) using unique empirical data to improve input parameters for applying state-of-the-art 3D numerical modelling and; (3) creating a simple guide for future ballistic assessments that considers available resources, field time and state of the volcano. Two case-study tourist volcanic centres in New Zealand are the basis of these investigations, due to pressing need for their ballistic hazard to be assessed. ...