Magmatic Carbon and Helium in Springs Reveals the Vitality of a Dormant Volcano, Taranaki, New Zealand

A challenge in monitoring long-dormant volcanoes is to discover early signs of reawakening. Mineral springs on Taranaki volcano (2,518 m, New Zealand) have elevated carbonate concentrations, delta C-13(DIC) similar to -5 parts per thousand (VPDB) and He isotopes from 5.13 to 5.92 R-A, indicating a magmatic volatile source. Stable isotopes demonstrate water recharge occurs near the volcano's summit. Volatile anions and silica are low in a cold (5(o)C) flank spring at 1,000 m a.s.l., yet elevated in warm springs (25-32(o)C) associated with travertine deposits at 250-300 m, suggesting a weak hydrothermal component along the flow path. Tritium dating of the cold spring water yields a mean residence time of 7.8 years. This short residence time and magmatic volatile signatures suggest magmatic CO2 persistently flushes Taranaki's upper edifice. Cold spring geochemistry thus reveals volcanic activity at this dormant volcano that otherwise lacks obvious geophysical signs of unrest.