Shock wave radon surface signals associated with the upsurge of T-P solitons in volcanic systems

The present paper introduces a theoretical model in order to describe groun d surface anomalies of radon emissions as a volcano is perturbed from its q uiescent (steady) state. Based upon modern thermo-poro-elasticity theory wh ich has been found to successfully explain rock deformation-fracturing, the se anomalies are considered as being due to the build up of a buried thermo -mechanical source which in turn gives rise to the upsurge of a thermo-mech anical (or T-P) soliton. This sort of fluid solitary wave, travelling upwar ds through induced deformed-fractured horizons. locally perturbes a pre-exi sting stationary radon concentration profile as the wave approaches the gro und surface. In order to model radon anomalies, a diffusive-convective tran sport equation of radon is adopted with Darcy's velocity change controlled by the upsurge of the T-P soliton. As a result, a new flow mechanism of rad on emission is found, which we call shock wave radon propagation. Some case s of volcanic eruptions which have been preceded and accompanied by anomali es in radon emissions are examined in the light of the model. A reasonably good agreement in the pattern between the observed radon concentration chan ges and the theoretical curves is found. A theoretical tool for volcanic su rveillance is thus proposed, corresponding to both an effort to shed more l ight on the correlations that map exist between geophysics and geochemistry of fluid emissions and the recognition, through ground surface radon anoma lies, of subsurface thermo-mechanical instabilities possibly preceding volc anic eruptions. (C) 2000 Elsevier Science B.V. All rights reserved.