Variations of ground radon concentrations with activity of Kilauea Volcano, Hawaii

Abstract

Measurements of the concentration of the radioactive gas radon, in particular relative areal variations in Rn outgassing (mainly isotopes ²²²Rn, t_1/2 = 3.82 days and ²²⁰Rn, t_1/2 = 54.5 s), at shallow ground depths (30 cm) are being used extensively in Hawaii in the exploration for geothermal resources^1,2. Zones showing a greater than usual degree of Rn ground gas outgassing have delineated areas of anomalous subsurface heat and increased permeability. The patterns of outgassing suggest that thermally induced ground gas convection systems have developed¹. Nine measurement stations have been established on the upper east rift of Kilauea volcano along the Chain of Craters Road (Fig. 1) to observe: (1) temporal variations in Rn outgassing; (2) relationship between Rn outgassing and variations in se ism i city; and (3) whether this technique can assist in understanding the ‘plumbing’ of Kilauea and whether monitoring of a larger number of stations could assist in indicating pre-eruptive activity. These nine stations, initially included in a summit-wide survey (August–September 1978), were re-established in Oktober 1979 because of the increased seismic activity within the upper east rift. Fortuitously, a small eruption of Pauahi Crater occurred on 16–17 November 1979 at the end of the first one-month period of measurement. The present results indicate that the Rn concentration increases before and during seismic events, then decreases before returning to a ‘normal’ value.