| dc.description | This paper reviews the nature and history of activity and the extent of risk at 14 volcanoes and volcanic centres in New Zealand and the Kermadec Islands. Mean intervals between eruptions are calculated, or estimated by extrapolation, for eight classes of eruption, represented by order of magnitude volume increases from 104m3 to 1011m3 (100 km3) Expected property losses in eruptions, divided by the approximate mean intervals, allow risk to be apportioned on an annual basis. In real terms the rhyolite volcanoes, between Kawerau/Lake Rotorua and the southern end of Lake Taupo, are easily the most destructive. Annually apportioned, however, the risk is highest for an eruption of about 107m3 at Mt Egmont.
Cumulative volumes erupted with time are estimated for most of the volcanoes and, where possible, average rates of magma accumulation and subsequent eruption have been estimated. This enables any shortfall between the actual volumes erupted, and the expected volumes, to be estimated, thus giving a measure of eruption potential at the present time. This varies for different volcanoes, from about 0.04 km3 up to several hundred cubic kilometres. The time elapsed since the last eruption, divided by the mean frequency for that class of eruption, gives an idea of the likelihood of further activity, although the usefulness of the results is limited by large standard deviations. In the short term, less than 100 years, an eruption of 107m3 at Mt Egmont again emerges as the most likely damaging event. In the medium term, of the order of a few hundred years, an eruption of c.1 km3 in the Okataina-Rotorua area, or in the district between Lake Taupo and Rotorua, becomes probable.
The data on which the conclusions are based, together with the mean intervals accepted, and the times elapsed since the last eruptions, are given in Appendices, so that the nature of the facts, and hence a wide perspective on volcanic activity in New Zealand, can be the better appreciated. The picture is one of volcanoes dormant for long periods of time, with great destructive potential, any of which could awaken at any time. | en-US |
