**4. Conclusions**

We describe the visual and seismic observations related to the onset of eruptive activity at White Island, New Zealand, for the period June to December 2012. The period included an explosive eruption, ash venting, and a dome emplacement episode through a 'wet' volcano hydrothermal system. The period was marked by persistent elevated tremor amplitudes and slowly evolving gliding spectral

lines. At the same time, the crater lake system progressively evaporated, which encompassed the full crater floor in June 2012 and progressed to isolated pools by the end of December 2012. Interestingly, this progressive lake loss promoted the next phase of mud/sulphur eruptions which began in mid-January 2013 [13–16] through the pre-existent Southeast vent system (Figure 2).

We regard the injection of magma into the shallow hydrothermal system as the key driver of the lake loss and shifts in tremor patterns in mid to late 2012. We interpret that the magmatic intrusion into the hydrothermal system began in early September and promoted the range of seismic observations documented here. Future work will be needed to examine the plausibility of the models outlined here with a rigorous analytical and numerical approach.

As a final note, the 9 December 2019 White Island eruption occurred within the timeframe of the development of this research and post-eruption unrest associated with that eruption is ongoing at the time of writing. Hence, this work does not include new insights from this most recent eruptive activity. At the conclusion of the present unrest period, a detailed retrospective assessment of the progression of unrest will be critical to determine similarities and di fferences for the two time periods. It is hoped that such an analysis will lead to ever-improving outcomes at di fficult to monitor volcanoes like White Island. The present work illustrates how persistent shallow magma and well-developed hydrothermal systems may produce observations that may fit many possible conceptual models and produce challenging monitoring conditions. It is a central goal of the volcano science community to document such events and hence to improve monitoring outcomes for similar volcanic systems both in New Zealand and around the globe. This work will help to assess the viability of the various models within the context of the limited available data.

**Author Contributions:** Conceptualization, A.J., C.C., T.G.; B.C., and R.C.; Data curation, A.J.; Formal analysis, A.J., C.C., T.G., and R.C.; Investigation, A.J., C.C., T.G., B.C., and R.C.; Methodology, A.J., C.C., T.G. and R.C.; Visualization, A.J., C.C., T.G., B.C., and R.C.; Writing—original draft, A.J., C.C., T.G., B.C., and R.C.; Writing—review and editing, A.J., C.C., T.G., B.C., and R.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This work used GeoNet seismic data which is freely available. All of the authors contributed toward manuscript and figure production as well as the data analysis and interpretation. Photos used in this study are from the GNS volcano database (VolcDB) and reflects the effort of the GeoNet team. A. Jolly and B. Christenson are supported by the Ministry of Business, Innovation and Employment (MBIE) Strategic Science Investment Fund (SSIF). T. Girona is supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by Universities Space Research Association under contract with the National Aeronautics and Space Administration. Chris Van Houtte and Tony Hurst reviewed an earlier version of the manuscript. We thank Alicia Hotovec-Ellis, William Chadwick, and a third reviewer for their useful comments which improved the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
