RADON-IN-SOIL VARIATIONS RELATED TO VOLCANIC ACTIVITY

Two active volcanoes, the Popocatepetl in Mexico, and the Piton de la Fournaise on the island of La Reunion, France, have been monitored for soil radon for several years. The Popocatepetl, located 60 km from Me xico City, started an eruptive period in December, 1994. Two radon-in- soil monitoring stations are operated there, since 1993. The behaviour of soil radon showed an increase as a function of the eruptive phase. The Piton de la Fournaise volcano has also been under survey for seve ral years. A radon network based on 20 Clipperton II automatic probes was set on July, 1994. Since then, the volcano has entered a quiescenc e phase. Thus it has been possible to draw the pattern of the radon be havior under the influence of atmospheric conditions.