Volcanic hazard in New Zealand: Scaling and attenuation relations for tephra fall deposits from Taupo Volcano

This paper is a first step in developing a probabilistic hazard model for tephra fall deposits in New Zealand. The data base consists of measurements of tephra thickness and eruptive volume from 32 past eruptive events at Taupo Volcano. From these are derived relations for the mean and maximum tephra thickness as a function of event volume and distance from the vent, and for the area enclosed by an isopach as a function of tephra thickness and volume. The directional effects due to wind do not vary appreciably over the volcanic region of New Zealand. The main feature of wind velocity is a flow to the east that becomes more consistent at higher altitudes. The larger the eruption, the more the location of the deposit of maximum thickness (the centre of deposit) tends to be displaced to the east of vent. A directional attenuation relation about the centre of deposit is derived from the Taupo data. This, in combination with a relation for the position of the centre of deposit relative to the vent, provides a means of estimating the probability of a given thickness of tephra fall deposit being exceeded at any distance and direction from the vent in an eruption of given volume.