Magmatic carbon and helium in springs reveals the vitality of a dormant volcano, Taranaki, New Zealand

Abstract

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, δ13CDIC ∼ −5‰ (VPDB) and He isotopes from 5.13 to 5.92 RA, 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 (5oC) flank spring at 1,000 m a.s.l., yet elevated in warm springs (25–32oC) 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.Plain Language SummaryDormant volcanoes with no obvious signs of activity are difficult to monitor. We show that the earliest released gas from magma, carbon dioxide, emanates from cold springs on the flanks of the dormant Taranaki volcano. The spring water is ∼8 years old when emerging and there were at least 10 eruptions recorded over the last millennium, suggesting that degassing of magma is happening now beneath Taranaki. Increases in the CO2 degassing from these sites could precede an eruption by months to weeks. Warm springs on the outer flanks of the volcano also show signs of being influenced by volcanic processes, providing new sites for potential volcano monitoring.