Hydrothermal Eruption Potential in Geothermal Development

Abstract

Hydrothermal eruptions are typical features of the Taupo Volcanic Zone high temperature geothermal fields. In the undisturbed systems, major deep-seated eruptions, originating as deep as 400 metres below ground surface can be expected every few thousand years, while small shallow focus events occur years apart. It is proposed that these shallow focus "eruptions" are in fact initiation events which can develop into the major deep-seated type of eruption where reservoir rock and fluid properties are favourable. While the probability of the small shallow focus events may be increased by field exploitation, the factors favouring deep-seated eruptions are reduced. However, as hydrothermal eruptions are characteristic of high temperature fields, their destructive potential should be considered in any development proposal.