Pressure gradient measurements in volcanic diffuse gas emanations

We describe a differential pressure measurement device which allows one to estimate fluid pressure gradients ranging from 6.3x10(-6) to 3.15x10(-3) at m/m in soil diffuse volcanic gas emanations. The lower limit roughly corres ponds to the atmospheric (static) pressure gradient due to gravity, and sho uld represent the minimum required value for volcanic gases to reach the Ea rth's surface by viscous flow. In the study of diffuse gas emanations, such as for the purpose of volcanic surveillance, such physical data supplement s the geochemical monitoring of concentrations and fluxes of specific subst ances constituting the flowing gaseous mixture and may be used to infer vol canic mechanical states. We describe: laboratory experiments with the devic e and report on a successful preliminary test with diffuse gas emanations o n the Miharayama cone of the Izu-Oshima volcano (Japan), where the highest fluid pressure gradients have been found to be associated with the highest CO2 fluxes and lowest CO2 concentration gradients.