Most of the trouble is due to the really high temperatures found at shallow depths; considerable steam or hot water pockets are not unusual at 400 to 600 feet. Here the pressure of the steam easily exceeds the weight of the drilling mud in the bore, leading to a blowout. Experienced drillers know how to shield such cavities with a cement mixture hard enough to resist the pressure. Because of the risk, it is usual to consolidate the area surrounding the pit by pouring grouting under pressure into little holes all around it so that the whole earth up to 100 feet deep is filled and hardened with cement. A power house is now being built to produce 69 megawatt, utilizing the steam only. The government is considering putting in further turbines bringing production up to 200–250 megawatts. Not only the steam, but also the hot water from the bores will be utilized, for this water (which constitutes the larger part of the bore output) will produce a vast quantity of steam when pressure is reduced. An important part of geothermal development is the measurement of output Below: A typical drilling site showing the elaborate precautions that are made to prevent blowouts (prevention equipment, cementing of the earth surrounding the bore). PHOTO: PETER BLANC and the careful keeping of detailed records. Some bores decline in output over a period probably due to cementing of the feeding fault zone by silica and other minerals carried in the water. So far there is no sign of the supply of hot water being overdrawn. Nobody knows what will happen when the hot water stored in the rocks is taken out. Will the flow of hot magmatic steam increase or is the flow constant and less than the present rate of steam extraction? Even in the least favourable case, the known reserves of stored heat at Wairakei will last for many years. It is also likely that there are other thermal areas in the graben where large supplies can be tapped. For instance, the mills of the Tasman Pulp and Paper Company, built near a known fault line at Kawerau, will probably ultimately have a geothermal power-plant of at least 20 megawatts, while in the near future geothermal steam is to be used for kiln drying of timber. Wairakei drilling crews have also started shallow drilling for a second geothermal steam station at Waiotapu, 20 miles from Rotorua. Will this solve the North Island's power problems? It is too early to say just what the final capacity of the volcanic plateau will be and New Zealand is not slowing down its efforts to bring power to the North Island by more orthodox means. It seems however that the cost of geothermal power generation will compete with that from hydro-electric dams, which alone justifies this new effort of man to exploit some strange resources below the surface of the earth.