Soil Rn-222 pulse during the initial phase of the June August 1995 eruption of Cerro Negro, Nicaragua

The June-August 1995 eruption of Cerro Negro, a small-volume basaltic cinder cone in Nicaragua, provided a unique opportunity to quantify Rn-222 degassing from soils in response to explosive volcanic activity. Rn-222 was monitored at 29 stations using electrostatically charged teflon Rn-222 detectors distributed north and southeast of the volcano, A pulse of elevated Rn-222 degassing occurred early in the eruption along a > 1 km long zone, extending least 750 m beyond the base of the cinder cone. Observation of this Rn-222 pulse shows that large changes in soil Rn-222 concentration can occur simultaneously at widely separated stations in response to even comparatively small-volume intrusions and volcanic eruptions. Frequent Rn-222 sampling at multiple stations provides a sense of the magnitude, time scales and area affected by convective gas transport during volcanic eruptions.