THERMODYNAMICS OF WATER-PERMEATED UNWELDED PYROCLASTS .2. NONEQUILIBRIUM PROPERTIES

Reported here are the results of an investigation of thermodynamic non -equilibrium properties of some Phlegraean unwelded pyroclasts. We exp erimentally determined: (a) hydraulic isothermal permeability of water -saturated samples; (b) thermal conductivity of the dry and liquid-per meated rock; (c) the effects produced by the superimposition of pressu re and temperature gradients to water-saturated samples. Throughout th e explored ranges of driving pressure and temperature, the hydraulic f low in porous rock samples has been found to be laminar. The thermal c onductivity of water-permeated porous rocks is strongly enhanced by lo cal convection occurring within the liquid-filled cavities. The superi mposition of pressure and temperature gradients in saturated samples i nduces characteristic non-linear temperature distributions dependent o n the intensity and orientation of the gradients as well as on the con stitutive properties of the solid and liquid phases and on boundary an d initial conditions. Interestingly, the temperature distribution with depth, found by drilling in the Phlegraean Fields area, nicely reprod uces the distribution produced by a liquid flux ascending from a burie d heat source. The phenomenological coefficients needed to apply the f ield equations to liquid-saturated soils in a temperature field are no w in our hands. Measurement of other coefficients relative to interact ions among gradients of pressure, temperature and electrochemical pote ntial may be obtained in a similar way. Accordingly, it should be now possible to develop a rigorous thermodynamic approach to the causes of Phlegraean bradyseism.