Report: TR 2020/05

Author: Bridget Lynne, Isaac J Smith and Gary J Smith (Geothermal Scientific Investigations Ltd)

Abstract

Ground Penetrating Radar (GPR) was undertaken over the southern section of the Armstrong Reserve, located in Taupo, New Zealand, to image the shallow subsurface. Historically, hot springs were located in this area. These springs discharged silica-rich, alkali-chloride water resulting in the formation of siliceous sinter terraces. No discharging hot springs are visible at the site today, although the historic sinter is exposed along the banks of a stream that dissects the study area. This stream is fed by thermal springs further upstream. GPR was used to image the buried sinter and to identify fractures within the sinter. The GPR data revealed three distinctive rock types in the subsurface; (1) unaltered siliceous sinter producing strong GPR reflections, (2) Rock Type B consisting of a poorly-reflective unit, (3) Rock Type C producing discontinuous horizons of strong reflections mixed with zones of poorly-reflective material. Fractures within the subsurface were also identified. GPR data was collected to a depth of eight metres along thirty-eight transect lines. Transects were arranged in a grid system to enable 3D modelling of the subsurface.