Ash fall prediction in New Zealand

Abstract

The North Island of New Zealand contains seven active volcanoes or volcanic centres, and ash fall from these centres could present health hazards and other problems. Part of the required contingency planning for ash fall is the assessment of the frequency and depth of ash fall at any point. The issue is particularly important for urban areas likely to be affected. This paper develops a theory for ash fall frequency assessment based on estimated eruption frequencies and magnitudes and on meteorological data. The theory is used to obtain the ash fall frequency/depth relationship for the Napier /Hastings area in the Hawkes Bay region. The results show that the annual frequency of significant ash fall in the towns is high enough to justify some degree of emergency preparedness, with a fall of 1 mm having an annual exceedance probability of about 0.05, or in other words a return period of approximately 20 years.