Decline in Rate of (Silica) Sinter Deposition in the Tokaanu Domain, Lake Taupo (NZ)

Abstract

Impressive quantities of (silica) sinter had deposited in a small area of the Tokaanu-Waihi geothermal field more than 135 years ago. The resulting sinter flats derived from large outflows of a few boiling pools and geysers discharging mainly deeply derived NaCltype water. The exposed sinter deposits decreased in area from at least 15,000 m2 in 1870/73 to c. 5,000 m2 in 1940 and to less than 800 m2 in 2007. Other thermal springs away from the old ‘source’ pools do not deposit sinter. The discharge rate of unmixed deep thermal water in the Tokaanu Thermal Park has declined since the 1870s and is now on the order of 3 kg/s, including c. 2 kg/s produced by a bath-house well. The discharge of unmixed and mixed thermal waters in the park is about 10 kg/s. Because of this decline, resumption of sinter deposition over the original area does not appear to be feasible but conservation of the remaining deep natural water supply is required instead and may result in localised restoration.