Geothermics Vol. 23, No. 5/6, p. 373, 1994 Pergamon CNR

Elsevier Science Ltd Printed in Great Britain

P R E F A C E 0375-6505/94 $7.00 + 0.00

The papers in this Speeiai Issue describe the results of scientific work carried out over the past three years in a number of active geothermal systems in the central part of the North Island of New Zealand. The systems are: Waimangu, Waiotapu, Waikite, "re Kopia and R ~ a . Some are suspected to be related, one of the purposes of this work was to try and resolve this question. All are distinguished by active thermal features, ranging from minor hot pools (Reporoa) to large crater lakes 0Vaimangu, Waiotapu). The Waimangu and Waiotapu systems contain a diverse range of well-developed thermal discharge features which have a protected status to allow development for tourist purposes. Indeed, these systems contain probably the finest New Zealand examples of silica terraces, hot springs, and fumaroles outside of the Rotorua Geothermal System. None of the geothermal systems described in this issue have been exploited.

Scientific interest in the systems has recently been revived because little published information has been available about them, and their extent and relationship to one another has been a mystery. Furthermore, being unexploited and some now protected, they offer the opportunity to determine the amplitude and frequency of natural changes which are occurring. This is important because it is not possible to interpret exploitation-induced changes (in other fields) until the natural changes are quantified. In New Zealand, such monitoring of natural changes before exploitation has never been done; commercial realities always seem to preclude this. Even at Broadlands (Ohaaki) Geothermal Fields where there was a long development period before exploitation began, this was not achieved. With developments for power generation now underway at Mokai, Rotokawa, and Tauhara, the number of geothermal areas available for long-term monitoring has been significantly reduced. Knowledge of the Waimangu, Waiotapu and Walkite systems has therefore become increasingly important.

Our colleagues Rick Allis and Tom Lumb, in their preface to the Rotorua Special Issue of GEOTHERMICS (vol. 21: 1/2: 1992), noted there was a lack of uniformity between authors of papers in that volume in the use of the terms geothermal system, field and area. This problem has still not been resolved. However, there is a general consensus amongst New Zealand scientists that the term geothermal system refers to the whole zone or region of geothermal effect, from the deep heat source to the surface; geothermal fields refers to the shallower part of the system which may (or may not) be affected by exploitation; geothermal area should be restricted to the surface manifestations. In defence of our lack of precision we point out that none of these terms are defined in standard geological glossaries. Readers may also note other inconsistencies between different papers in this issue. We have taken the view, rightly or wrongly, that it is not our job to impose particular concepts or definitions, but it is the duty of authors to communicate with each other and to take responsibility for their work.

We thank the authors and reviewers for their efforts to meet our deadlines, Diane Hewitt and Joanne Rogers of the Wairakei Research Cenlre for assisting with compilation of the issue, and Marnell Dickson of GEOTHERMICS for her support. We also thank the New Zealand Foundation for Research, Science and Technology for providing the funds for much of the scientific work and the compilation of this issue.

Trevor Hunt and Richard Glover Institute of Geological and Nuclear Sciences Wairakei Research Centre Private Bag 2000 Taupo New Zealand

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November 1994