Insights Into Magmatic Degassing, Hydrothermal Dynamics, and Eruption Precursors From Long Term SO ₂ Emission Monitoring at Whakaari/White Island, New Zealand

Abstract Long‐term SO 2 emission rate time series are critical for deciphering the subsurface processes regulating open‐vent volcanoes, yet extracting cyclical drivers from continuous degassing records remains challenging. We analyze a 14‐year (2006–2020) SO 2 emission rate data set from Whakaari/White Island, New Zealand, identifying five chronological degassing phases. Results reveal a magmatic‐hydrothermal duality: high‐rate emissions persist through open pathways while the surrounding matrix actively seals, trapping fluids and driving localized overpressure. Notably, the 2019 pre‐eruption period shows a systematic, multi‐month baseline increase exceeding the 95th percentile threshold (800 t/day) months prior to the event. Wavelet analysis identifies variable short‐term periodicity during unrest alongside robust cycles at ∼565 and ∼1,275 days. The ∼565‐day cycle broadly mirrors regional slow slip recurrence, suggesting potential tectonic forcing, whereas the ∼1,275‐day cycle reflects coupled deep reservoir supply and shallow conduit overpressure timescales. This framework enhances hazard assessments at open‐vent magmatic‐hydrothermal systems.