Helium in fumarole and well gases as an index of long-term geothermal potential

We have used fumaroles and degassing vents around Kilauea volcano as models of producing geothermal areas. Excess helium has been found in gases from fumaroles characterized by long-term activity, and is absent in gases from short-lived hot spots, from dry vents or fissures formed by recent activity, and from old degassed lava lakes. From this it is inferred that the absence of helium in gases from geothermal areas would indicate that they receive heat from a limited magma body, and would be expected to yield extractable heat for only a comparatively short period. The geothermal well at Puna, Hawaii, has given positive helium indications.Work performed under support from grants from the Hawaii Natural Energy Institute and the National Science Foundation, Grant EAR73-00201-A02