Monitoring of Geyser Activity in Whakarewarewa, New Zealand

Abstract

We carried out monitoring of self-potential (SP) and gravity in Whakarewarewa geothermal field, New Zealand. Seven electrodes were set around the major geysers, Prince of Wales Feathers, Pohutu, Waikorohihi and Mahanga. One SCINTREX CG-3M gravity meter was set near Te Horu cauldron, the water level of which was monitored using a capillary-tube type pressure gauge. We observed remarkable SP changes well correlated with the eruptions of Pohutu Geyser and the water level change of Te Horu. At one electrode near the geyser vent, SP increased suddenly by about 50 mV immediately before the each eruptions, decreased rapidly by 20-40 mV corresponding to the each ends of eruption and returned gradually to the original level. Although the electrokinetic effects is thought to be responsible for a part of observed signals, the mechanism of the SP changes is not fully understood at present.