A new investigative approach to understanding fluid flow migration pathways within the shallow subsurface at Orakei Korako, New Zealand

Abstract

Sinter analyses, infrared imaging, downhole temperature measurements and Ground Penetrating Radar (GPR), were undertaken in 2012 at Orakei Korako, Taupo Volcanic Zone, New Zealand to investigate the inter-relationship of chemistry, temperature and texture of sinters at shallow subsurface depths (<5 m). Sinter mineralogy and morphology was used to distinguish sinter affected by postdepositional overprinting of acidic steam condensate from unaltered sinter. Ground Penetrating Radar (GPR) imaged strong-amplitude reflections over unaltered sinter deposits and weak-amplitude reflections where the sinter had been altered via acidic steam condensate. GPR also imaged subsurface discontinuities interpreted as conduits for ascending steam, which were confirmed by measured downhole temperatures of >90˚C. Infrared imaging of individual sites within the geothermal area provided further information on surface temperatures at Orakei Korako. This new multi-method approach identified: (i) areas of heat in the subsurface where there is no present-day evidence of heat in the shallow surface, and (ii) areas of sustained heat in the subsurface as evidenced by the high level of acidic steam condensate overprinting of surface sinter deposits. Repeated surveys will identify if the surface and shallow subsurface conditions mapped in 2012 are changing and map areas of the field that are heating up or cooling down with time.