Probabilistic tephra fall simulation for the Auckland Region, New Zealand

C. R. Magill*, A. W. Hurst, L. J. Hunter, R. J. Blong

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)


The Auckland Region, New Zealand is at significant risk from tephra falls originating both from the local Auckland Volcanic Field (AVF) and several distant, large-volume centres. We use geological data and observations of historical eruptions to develop a catalogue of simulated tephra dispersal patterns for the Auckland Region, using the ASHFALL model. Simulated patterns relate to individual eruptive phases and can be combined to simulate events that vary in volume and duration. AVF eruption parameters were chosen to replicate fine tephra fall dispersed from small-volume phreatomagmatic eruptions. Modelling of eruptions from distant volcanoes was carried out in two stages. First, the sensitivity of modelled tephra thickness to various model parameters was tested. By far the largest thickness variations were the result of varying wind conditions, followed by eruption volume. The second stage involved modelling volumes that best replicated thicknesses of preserved events within the Auckland Region, allowing the catalogue to be created. Only about 1% of simulations from distant volcanoes reached the Auckland Region, suggesting that preserved tephra layers are either the result of reasonably long-lived eruptions or a number of eruptive phases. For eruptions originating within the AVF, mean modelled tephra thickness on land is small-approximately 1.6 mm near the coast and thinning rapidly inland. Mean andesitic thicknesses are dominated by eruptions from Egmont volcano, which typically deposit tephra over a narrow section of the Auckland Region with a maximum thickness of approximately 1.7 mm. Rhyolitic eruptions are more widespread, with mean thickness varying from 30 mm in the south of the Region to 9 mm in the north. When all centres are combined and weighted by their conditional likelihood of occurrence, mean thickness ranges from 7 mm in the south to 1.5 mm in the north. However, maximum thicknesses of 150 mm for the AVF, 12 mm for andesitic centres and 830 mm for rhyolitic centres all have the potential to cause much greater damage within parts of the Auckland Region.

Original languageEnglish
Pages (from-to)370-386
Number of pages17
JournalJournal of Volcanology and Geothermal Research
Issue number3-4
Publication statusPublished - 15 May 2006


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