Measurement of heat flux from steaming ground

The total thermal flux at the surface of 'steaming ground' consists of a convective and a conductive component, even in the absence of any visible steam discharge at the surface. The total flux and its convective component can be measured separately and directly using a water-filled ground calorimeter. The conductive component is given by the difference between the two fluxes, but can also be assessed independently using measured near-surface soil parameters and temperature gradients, retaining the thermal conductivity as parameter. The conductivity is controlled, in turn, by the thermal diffusivity and the specific moisture content of the near-surface layer. The observed total flux values range between 0.03 and 2 kW/m2 at sites where boiling temperatures occur at depths of about 4 m and <0.1 m, respectively; the convective flux can reach 50% of the total flux at most sites. Analysis of various soil parameters and soil temperature sections points to a 'heat pipe' transfer mechanism that maintains a high conductive transfer in a thin near-surface layer where sub-surface steam condensation is enhanced. An empirical power-law function can be used to assess the total heat flux from the boiling point depth at single sites with known soil temperature profiles.