Tony Hurst

Factors Influencing Volcanic Ash Dispersal from the 1995 and 1996 Eruptions of Mount Ruapehu, New Zealand

Abstract The prediction of the dispersal of volcanic ash from events such as the Ruapehu eruptions of 1995 and 1996 is important, not only for civil-defense authorities who need to warn people in downwind areas, but for airline companies that have to reroute aircraft to avoid the encounters with volcanic ash clouds that can badly damage expensive jet engines and jeopardize passenger safety. The results of numerical simulations of volcanic ash dispersal using the Regional Atmospheric Modeling System (RAMS) and Hybrid Particle and Concentration Transport Model (HYPACT) for three periods (11–12 October 1995, 14 October 1995, and 17 June 1996) during the recent Ruapehu eruptive sequence are presented here. RAMS is a 3D atmospheric model that can be used to give detailed predictions of winds for regions such as the volcanic plateau. HYPACT is a particle dispersion model that uses the RAMS-generated wind fields to predict the movement and concentration of the volcanic ash cloud. Validation is achieved through c...

Volcanic ashfall in New Zealand – probabilistic hazard modelling for multiple sources

Abstract The airfall ash component of the New Zealand Probabilistic Volcanic Hazard Model (PVHM) estimates the likelihood of volcanic ash deposits of any given thickness at any site, based on the frequency-magnitude relations of all the significant volcanic sources in New Zealand and the wind distribution statistics. The main source of error in these models is the uncertainty in the historic ash production records of the volcanoes. Another source of error is that the current wind pattern may not be the same as during the period that the observed ash record was deposited. The spatial distribution and magnitude/frequency curves of volcanoes are very different from those of earthquakes, and this is reflected in the hazard models. Whereas a typical probabilistic earthquake hazard model will have the expected acceleration increase by a factor of 3 to 5 between 500 and 10,000 year return periods, the expected ash thickness can change by up to a factor of 1000 over these periods. The Auckland Volcanic Field is now occupied by New Zealands largest city, so the comparatively small and infrequent eruptions potentially represent a major social and financial hazard. Our modelling of lake core ash records in the Auckland area suggests that the known vents and eruptions probably represent less than half of the total volcanic activity from the field, and that the hazard from local events is comparable to that from more distant sources. An area needing improvement is the hazard in Auckland from local eruptions, with more ash thickness data and better basaltic eruption models.

Feasibility study for geodetic monitoring of Mt Ruapehu volcano, New Zealand, using GPS

Abstract Global Positioning System (GPS) receivers were installed on Ruapehu volcano for a 10 month experiment to determine their utility for providing continuous real‐time deformation monitoring. Several processing runs were carried out to study the effects of ionospheric and tropospheric modelling and the use of predicted orbits on the noise levels of relative position determinations between receivers in the GPS network. Lowest noise levels were achieved with a system that solved for relative tropospheric delay between stations, and created a local ionosphere model using a dual frequency receiver. The use of predicted orbits rather than more accurate post‐processed orbits did not degrade the solutions for this small‐scale (6 km dimension) network. Our results imply that a real‐time system would detect relative vertical deformation that exceeds 25 mm and relative horizontal deformation that exceeds 10 mm over a several week period. Modelling of expected deformation leading to a small, shallow‐source (c. 1 km) eruption, with an associated pressure change of 106 Pa, indicated maximum vertical displacements of 40–70 mm could be expected at 300–600 m from the conduit centre, with horizontal displacements of 15–45 mm at 300–700 m. Such changes would be detectable by a real‐time GPS monitoring system.

Conceptual Development of a National Volcanic Hazard Model for New Zealand

We provide a synthesis of a workshop held in February 2016 to define the goals, challenges and next steps for developing a national probabilistic volcanic hazard model for New Zealand. The workshop involved volcanologists, statisticians, and hazards scientists from GNS Science, Massey University, University of Otago, Victoria University of Wellington, University of Auckland, and University of Canterbury. We also outline key activities that will develop the model components, define procedures for periodic update of the model, and effectively articulate the model to end-users and stakeholders. The development of a National Volcanic Hazard Model is a formidable task that will require long-term stability in terms of team effort, collaboration and resources. Development of the model in stages or editions that are modular will make the process a manageable one that progressively incorporates additional volcanic hazards over time, and additional functionalities (e.g. short-term forecasting). The first edition is likely to be limited to updating and incorporating existing ashfall hazard models, with the other hazards associated with lahar, pyroclastic density currents, lava flow, ballistics, debris avalanche, and gases/aerosols being considered in subsequent updates.

Forecasting volcanic ash deposition using HYSPLIT

A major source of error in forecasting where airborne volcanic ash will travel and land is the wind pattern above and around the volcano. GNS Science, in conjunction with MetService, is seeking to move its routine ash forecasts from using the ASHFALL program, which cannot allow for horizontal variations in the wind pattern, to HYSPLIT, which uses a full 4-D atmospheric model. This has required some extensions to the standard version of the HYSPLIT program, both to get appropriate source terms and to handle the fall velocities of ash particles larger than 100 microns.Application of the modified HYSPLIT to ash from the Te Maari eruption of 6 August 2012 from Tongariro volcano gives results similar to the observed ash distribution. However, it was also apparent that the high precision of these results could be misleading in actual forecasting situations, and there needs to be ways in which the likely errors in atmospheric model winds can be incorporated into ash models, to show all the areas in which there is a significant likelihood of deposited ash with each particular volcanic eruption model.