Forecasting the consequences of the failure of the eastern rim of Crater Lake, Mount Ruapehu : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Earth Science at Massey University, Palmerston North, New Zealand

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Date
2011
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Massey University
Abstract
A numerical code for simulating dry flows of granular material, Titan2D, was used to model a range of possible collapse scenarios and resulting debris avalanches from a possible failure of the eastern crater rim of Mount Ruapehu, New Zealand. The eastern rim of Crater Lake, Mount Ruapehu consists of a stratigraphic sequence of intercalating volcaniclastic diamictons, pyroclastics and lavas, some of which are highly hydrothermally altered. This rim is under outward pressure from Crater Lake and constitutes one of the steepest parts of the active volcano. Its sudden failure could involve up to 50 million m³ of rock material, almost certainly generating a debris avalanche and/or a break-out lahar up to 9 times the size of the March 2007 event. A failure of hydrothermally altered flank materials on this side of the volcano has already occurred (c. 4600 yrs Mangaio Fm. (Donoghue & Neall, 2001)). A quantitative hazard and risk analysis of this scenario has never been undertaken, despite ongoing hydrothermal alteration and considerable sapping of both the inside and outside of the rim from explosive eruptions and base surges during the 1995/1996 and 2007 eruptions. New stratigraphic data were integrated with existing high-resolution topographic information and aerial photography to produce a detailed map of the eastern rim to highlight the distribution of contrasting stratigraphic sequences and the distribution of those units with the largest degree of alteration. This information was used as the first step towards defining the likelihood of different failure volumes and geometries to be tested in numerical hazard simulations. A quantitative scenariobased hazard forecast for partial or full collapse of the crater rim and subsequent events was determined. Simulated data of flow run out, inundation, diversion, velocity and mass transport were analysed to identify the resulting hazards for the Whangaehu and Tongariro River catchments. The results of this research suggest that the Mangatoetoenui, Upper Waikato, Tongariro and Whangaehu River catchments could be greatly affected by a sudden collapse of the eastern rim and any subsequent lahar events.
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The appendices are on a CD-ROM which is held with the vault copy of the thesis. Appendices include logbook, lab work, Titan2D data and simulation videos.
Keywords
Volcanic hazard analysis, Tongariro National Park, Titan2D, Computer simulation, Volcanic activity
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