An assessment of ballistic hazard and risk from Upper Te Maari, Tongariro, New Zealand (2014)
Type of ContentTheses / Dissertations
Degree NameMaster of Science
PublisherUniversity of Canterbury. Department of Geological Sciences
Explosive volcanic eruptions frequently expel ballistic projectiles, producing a significant proximal hazard to people, buildings, infrastructure and the environment from their high kinetic and thermal energies. Ballistic hazard assessments are undertaken as a risk mitigation measure, to determine probabilities of eruptions occurring that may produce ballistics, identify areas and elements likely to be impacted by ballistics, and the potential vulnerabilities of elements to ballistics.
The 6 August, 2012 hydrothermal eruption of Upper Te Maari Crater, Tongariro, New Zealand ejected blocks over a 6 km2 area, impacting ~2.6 km of the Tongariro Alpine Crossing (TAC), a walking track hiked by ~80,000 people a year, and damaging an overnight hut along the track. In this thesis ballistic hazard and risk from Upper Te Maari Crater are assessed through a review of its eruptive history, field and orthophoto mapping of the 6 August ballistic impact distribution, forward modelling and analysis of possible future eruption scenarios using a calibrated 3D ballistic trajectory model, and analysis of the vulnerability of hikers along the impacted Tongariro Alpine Crossing.
Orthophoto mapping of the 6 August ballistic impact crater distribution revealed 3,587 impact craters with a mean diameter of 2.4 m. However, field mapping of accessible regions indicated an average of at least four times more observable impact craters and a smaller mean crater diameter of 1.2 m. By combining the orthophoto and ground-truthed impact frequency and size distribution data, it is estimated that approximately 13,200 ballistic projectiles were generated during the eruption.
Ballistic impact distribution was used to calibrate a 3D ballistic trajectory model for the 6 August eruption. The 3D ballistic trajectory model and a series of inverse models were used to constrain the eruption directions, angles and velocities. When combined with eruption observations and geophysical observations and compared to the mapped distribution, the model indicated that the blocks were ejected in five variously directed eruption pulses, in total lasting 19 seconds. The model successfully reproduced the mapped impact distribution using a mean initial particle velocity of 200 m/s with an accompanying average gas flow velocity over a 400 m radius of 150 m/s.
Assessment of the vulnerability of hikers to ballistics from the August eruption along the TAC utilised the modelled spatial density of impacts and an assumption that an average ballistic impact will cause serious injury or death (casualty) over an 8 m2 area. It is estimated that the probability of casualty ranged from 1% to 16% along the affected track (assuming an eruption during the time of exposure). Future ballistic hazard and vulnerability along the TAC are also assessed through application of the calibrated model. A magnitude larger eruption (than the 6 August) in which 10x more particles were ejected, doubled the affected length of the TAC and illustrated that the probability of casualty could reach 100% in localised areas of the track. In contrast, ballistics ejected from a smaller eruption did not reach the track as was the case with the 21 November 2012 eruption. The calibrated ballistic model can therefore be used to improve management of ballistic hazards both at Tongariro and also, once recalibrated, to other volcanoes worldwide.
Keywordsballistic; Tongariro; impact crater; ballistic trajectory model; volcanic hazard; risk
RightsCopyright Rebecca Hanna Fitzgerald
Showing items related by title, author, creator and subject.
Ballistic impact crater modelling using UAV and structure from motion technology : 2012 Te Maari volcanic eruptions, New Zealand Pitchika, Ravitej (University of Canterbury, 2017)New Zealand has a strong historical background of producing volcanic eruptions and earthquakes due to its geographical setting. The deformation caused by the collision of Australian and Pacific plates has given rise to New ...
Mapping and modelling phreatic ballistic fields at tourism hotspots : a methodological assessment at Tongariro and Whakaari (White Island) Volcanoes, New Zealand. Gates, Stephanie Louise (University of Canterbury, 2018)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% ...
Multi-volcanic Hazard Impact Assessment for Residential Buildings in the Auckland Volcanic Field, New Zealand Allen, Nicole; Wilson, Thomas; Kennedy, Ben; Scott, Allan; Stewart, Carol (2019)Volcanic eruptions can produce many hazards which can impact society yet many cities, including Auckland, are built on or near active volcanoes. Auckland rests on the Auckland Volcanic Field (AVF), an active volcanic field ...