Radon gas can be used as an effective tracer to predict volcanic activity and, in some cases, it can also be a precursor of earthquakes. This is what emerges from a new study published in Geochemistry, Geophysics, Geosystems, and carried out by researchers at the Etna Observatory of the National Institute of Geophysics and Volcanology – INGV. See the article.
I heard this several years ago, but it is interesting,
A customer of mine used to participate if International scientific ocean surveys, during which he measured radon in seawater to determine water density.