Numerical modelling of Pohutu geyser, Rotorua, New Zealand

Thus, although the geysers at Rotorua, New Zealand have shown some natural variation in their behaviour, they have also been significantly affected by human interference. The aim of this study is to quantify the past response of geyser activity to human-induced changes in the state of the Rotorua geothermal reservoir and to provide a tool for predicting the future behaviour of the geysers. The study is based on a simple computer model of a geyser that consists of a chamber linked to cold recharge and deeper hot recharge. The chamber also has an outlet to the surface through a narrow channel. The TOUGH2 simulator is used to carry out many numerical experiments to determine how parameters such as the size of chamber, cold recharge pressure, hot recharge pressure and permeability of the channel affect whether or not the model produces geysering behaviour and how they affect the period of the eruptions. The model successfully matches the observations that: (i) geysering ceases if hot recharge diminishes, (ii) the frequency of eruption increases if hot recharge increases and (iii) if hot recharge increases enough, then geysering turns into continual spouting.