Thermal Properties of Steaming Ground (Wairakei Field, NZ)

Abstract

Shallow temperature monitoring and soil sampling in areas of steaming ground at Wairakei and Tauhara have revealed that the thermal dzmiviiy of these pumice soils averages about 0.4 E-6 m2/s. The thermal conductivity varies between 0.4 and 1.4 W/mK, in response to variations in moisture content of 100 to 700 kg/m3. Vertical temperature gradients, and therefore conductive heat losses, are linearly related to the temperature above ambient, by a factor that decreases with depth. Convective heat transfer dominates above about 7OoC. Twice-daily temperature pulses rising towards the surface are triggered by steam from subsurface boiling caused by periodic pressure waves originating in the upper atmosphere. These merge with downward pulses of diurnal solar heating, complicating the assessment of soil difbivity.