Simulation of the 2012 Te Maari debris avalanche: insight into the failure mechanics and the role of the hydrothermal system.
Juliette Vicente1 , Stuart Mead1, Gabor Kereszturi1, Craig Miller2.
Affiliations: 1 School of Agriculture and Environment, Massey University, Palmerston North, New Zealand ; 2 GNS Science, Wairakei Research Centre, Taupo, New Zealand.
Presentation type: Talk
Presentation time: Tuesday 16:15 - 16:30, Room R280
Programme No: 3.5.11
Abstract
The generation of volcanic mass flows is driven by various initiation processes that result from a combination of preparatory and triggering factors. These initiation conditions largely affect flow dynamics including landslide mobility and runout distance, which pose significant risks to nearby populations and infrastructures. Tongariro, an active andesite volcano, experienced one of New Zealand's most recent debris avalanches at the Upper Te Maari crater on August 6, 2012. This debris avalanche released a volume of 7 × 105 m3 of material from the source, which by unloading the pressurised vapour-dominated hydrothermal system, led to a phreatic eruption. We use finite-element modelling to identify causes of the Te Maari slope failure, and assess the sensitivity to varying groundwater, seismic and mechanical conditions. Model results closely match the observed failure when considering the strength of hydrothermally altered rocks subjected to an increased pore pressure at shallow depth. We found that even a relatively minor rise in pore pressure, ≈ 200 kPa in the upper layers, could replicate the observed failure at Te Maari. Our simulations also reveal that this debris avalanche might be a multiple-stage failure involving the progressive sliding of two distinct blocks. These findings better constrain preparatory and triggering factors that affect avalanche flow and emplacement, improve our understanding of Tongariro's mass flow deposits and enhance hazard assessments for future potential collapses at Tongariro and other volcanoes with hydrothermal systems.