CONTINUOUS MEASUREMENTS OF RADON CONTENT IN GROUNDWATER ON THE VOLCANIC SITE OF PITON-DE-LA-FOURNAISE (ISLAND-OF-REUNION, FRANCE)

In the framework of the ''R.E.M.M.I.'' programme (French programme to study the ship relation between water and magma in intertropical envir onment), different physical and chemical parameters (radon level, cond uctivity, pH, CO2 level, helium level, temperature) are monitored in t he drainage waters of the ''Tunnel de la Riviere de l'Est'' in order t o correlate their variations with the stress in the volcanic chain of the ''Piton de la Fournaise''. In a first period of experimentation, d uring the dry season, the radon concentrations in water have been meas ured by nuclear track detectors (LR115). In a second field session, du ring the wet season, a complementary technique has been added. a conti nuous measurement with a portable proportional counter. The radon meas urements and the other results suggest potential for continuous monito ring, through various time steps of the annual cycle likely to be indi cators of volcanic activity. This second phase should begin in 1992, S eptember in a new European Programme.