Volcanic Hazard in New Zealand: Scaling and Attenuation Relations for Tephra Fall Deposits From Taupo Volcano

Abstract

This paper is a first step in developing a probabilistic hazard model for tephra fall deposits in New Zealand. The database consists of measurements of tephra thickness and eruptive volumefrom 32 past eruptive events at Taupo Volcano. From these are derivedrelations for the mean and maximum tephra thickness as a function ofevent volume and distance from the vent, and for the area enclosed byan isopach as a function of tephra thickness and volume. Thedirectional effects due to wind do not vary appreciably over thevolcanic region of New Zealand. The main feature of wind velocity is aflow to the east that becomes more consistent at higher altitudes. Thelarger the eruption, the more the location of the deposit of maximumthickness (the centre of deposit) tends to be displaced to the east ofvent. A directional attenuation relation about the centre of deposit isderived from the Taupo data. This, in combination with arelation for the position of the centre of deposit relative to thevent, provides a means of estimating the probability of a giventhickness of tephra fall deposit being exceeded at any distance anddirection from the vent in an eruption of given volume.