Heat Transfer of the Karapiti Fumarole Field (1946- 2000)

Abstract

Improvements in heat transfer calculations for the Karapiti fumarole field are described. Heat loss from conduction, evaporation and direct steam discharge can be assessed using airphotos and infrared surveys. Analyses of 22 air-photos since 1946, and 5 infrared surveys since 1989, are used to map changes in steam discharge, areas of hot ground and areas of thermally tolerant vegetation. The linear relationship between heat loss and normalized steam cloud area observed in recent studies has been applied to older fumarole studies and air-photos. Large changes in heat flux occurred at Karapiti during the first 25 years (from 1950), but changes have been more gradual since 1975. The source of deeper vapour flux has apparently migrated southwards over this period. The heat output of all fumaroles is assessed to have increased from about 30 MW (1 950) to 235 MW (1960) then decreased gradually to c. 100 MW (2000). The total heat loss for Karapiti in 2000 is assessed to be c. 200 MW, 50% from conductive losses and 50% from steam discharges.