Interpreting SP Anomalies in a Changing Hydrothermal System on White Island, New Zealand
Abstract
White Island, in the Bay of Plenty, NZ is the emergent summit of a submarine stratovolcano that lies on the offshore north-eastern tip of the Taupo Volcanic Zone. The island hosts a well-developed hydrothermal system, including a hyper-acidic crater lake, acid springs, and energetic fumaroles.
In July 2017, we undertook an electrical self-potential (SP) survey at White Island. The survey focused around the vigorously degassing Fumarole 0, which is thought to represent a direct degassing conduit from the magma reservoir. We measured four linear arrays, approximately 100 meters in length, arranged in a spoke-like pattern centred around the fumarole. Preliminary results show a positive SP anomaly near the fumarole with progressively negative values moving radially outward. The low positive values (<10 mV) imply some hot upflow of fluid near Fumarole Zero. However, negative values (>-125mV) suggest some interplay of cooler downflow and changes in salinity and gas saturation in the subsurface. ;A similar radial survey was taken in September 2015; however, those results suggest a markedly different flow regime with negative anomalies adjacent to Fumarole Zero and progressively more positive values moving away. Interestingly, the 2015 survey occurred just days prior to a period of renewed unrest, which was marked by increased gas emissions, volcanic tremor, and ground deformation. This unrest continued for six months, leading to a hydrothermal eruption in April 2016. nd a permanent acid lake had again developed inside the with those from previous SP surveys and records of unrest suggests that fluid flow conditions within the hydrothermal system change prior to volcanic activity. This study investigates whether a pattern exists between a change in fluid flow regimes and the onset of volcanic/hydrothermal activity. Considering recent advancements by Christenson (2017) on the evolution of the hydrothermal system at White Iland, this work explores the interpretation of SP anomalies in active, high temperature, volcano-hydrothermal systems.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMNS41A0810S
- Keywords:
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- 0920 Gravity methods;
- EXPLORATION GEOPHYSICSDE: 0925 Magnetic and electrical methods;
- EXPLORATION GEOPHYSICSDE: 0935 Seismic methods;
- EXPLORATION GEOPHYSICSDE: 1835 Hydrogeophysics;
- HYDROLOGY