Water and Steam
Ground water is a mineral of the greatest importance to New Zealand: for human consumption, for secondary industry, and, in particular, for the primary agricultural industry. Fortunately, the abundant rainfall in most areas and the common presence of gravels, sands, fissured volcanic rocks, and cavernous limestones, afford plentiful supplies of ground water in many areas. Elsewhere lesser quantities are obtained from sandstones, or fractured harder rocks, but in some areas, where only clays and impermeable fine-grained rocks such as mudstones (papa) are within the range of normal drilling, an adequate supply of ground water is not possible. Artesian water is important in the seaward Canterbury Plains, and in the lowlands of the southern North Island. It is, by definition, ground water that occurs naturally under pressure and is usually present in a sloping gravel bed beneath an impermeable clay cover.
Most underground water is of good quality. Some is warm or hot, and hot springs are relatively widespread and are particularly common in the recently active volcanic regions. From Taupo to White Island geysers and hot springs have long implied a possible potential for power development from geothermal steam. Investigations began seriously in 1950, and a 150 mW station, with plans for further development, has been erected at Wairakei. There are hopes that the combined potential at Waiotapu, Orakeikorako, Rotokawa, Tikitere, and Te Kopia may prove to be about three times that of Wairakei.
by David Kear, B.SC.(MINING)(LOND.), A.R.S.M., New Zealand Geological Survey, Otahuhu.