No abstract

No abstract

Weekly readings of ground temperatures to a depth of 6' I) metres were made at Wairakei, New Zealand, between 195R and 1962. These readings were supplemented by multi-point Brown potentiometer recordings to a depth of 3 m for more than a year. Air temperatures were also available for the five-year period. Results show that the mean annual air temperature was 12°c; the range of the diurnal variation (from max. to min.) was less than 1 deg C at depths greater than 30 cm; the range of the seasonal variation was less than 1 deg c at depths greater than I) m; the mean annual temperature at a depth of 1 m was 3 deg c greater than the mean annual air temperature; the mean annual thermal dilfusivity and conductivity were 3' 5 X 10-3 cm'/sec and 11) X 10-' cal/sec cm deg c respectively; the thermal conductivity of the pumice soil varied with moisture content, being 40 X 10-' cal/sec cm deg c when the water content was 73i% by volume (voids completely filled with water) and 4 X 10-' cal/sec cm deg c when the water content was 5 %; and the mean annual geothermal heat flux at the surface was 40 X 10-6 cal/cm 2 sec, which is about 40 times the world average.

The variation of ground temperature with depth was measured between 1954 and 1961 at numerous locations in the Wairakei thermal area of New Zealand. Analysis of these data clearly shows that conduction is the dominant mechanism of heat transfer until the difference between the temperatures at the surface and at a depth of 1 metre reaches a value of about 25 deg c. For higher ground temperatures, heat transport by convection of a mixture of air and water vapour becomes progr,essively more important and the conductive effect becomes insignificant. These conclusions are used to present a simplified picture of the nature of the mechanisms in the transfer of heat to the surface in areas of steaming ground at Wairakei. The temperature data are also used to study the geothermal microclimate, to determine the thermal conductivity of the soil, and to derive relations between the temperatures at various

No abstract