Fig. 9
From: In-situ monitoring of 3He/4He in summit gases of Kilauea Volcano (Hawaii) prior to the 2020 eruption
Timeseries of 4He concentration (in ppm) in vent gas collected at the Old Well and New Well sites from early 1970 until late 2020. Data sources are noted. Except for the standard deviation error bars of Naughton et al. (1973), we report the mean and range of concentrations for the monitoring period, the latter denoted as horizonal bars. Also reported are the number of samples and the method used to determine the helium values (GC: gas chromatography, MS: mass spectrometry). The red solid curve is a suggested long-term trend to these data. The green solid line indicates the average air concentration