Soil222Rn 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 222Rn degassing from soils in response to explosive volcanic activity. 222Rn was monitored at 29 stations using electrostatically charged teflon 222Rn detectors distributed north and southeast of the volcano. A pulse of elevated 222Rn degassing occurred early in the eruption along a > 1 km long zone, extending at least 750 m beyond the base of the cinder cone. Observation of this 222Rn pulse shows that large changes in soil 222Rn concentration can occur simultaneously at widely separated stations in response to even comparatively small-volume intrusions and volcanic eruptions. Frequent 222Rn sampling at multiple stations provides a sense of the magnitude, time scales and area affected by convective gas transport during volcanic eruptions.