by Cécile Massiot, Stephen Craig Cary, Craig Miller, Pilar Villamor

Caldera volcanoes produce Earth’s largest explosive eruptions, generate seismicity both independent and associated with unrest and eruptive periods, host mineral and geothermal resources that interact with groundwater, and support a largely unexplored biosphere. Many silicic calderas are hosted in an active rift. Volcanic, tectonic, hydrologic and biosphere processes in calderas are intimately connected, yet poorly understood, and require subsurface observations. We hypothesise that the history of interplay between tectonic and magmatic processes across caldera/rift intersections explains differences in hydro-bio-processes inside, outside, and at the margins of calderas. We also propose that precursors to caldera unrest can be detected early in drillholes by changes in crustal strain; fluid properties; and, in what would be a world first, exploring the possibility of using microorganisms as subsurface biosensors. The Okataina Volcanic Centre (OVC) is one of two giant active calderas in the Taupo Volcanic Zone, Aotearoa New Zealand. The OVC is ideal for scientific drilling and as a testbed for novel volcano monitoring approaches. It combines high eruption rate, frequent unrest events and earthquake swarms, location in a densely faulted rapidly extending rift, diverse groundwater-geothermal fluid circulations, and large variety of surface microbiota. CALDERA proposes a 2-drillhole strategy at the OVC to significantly advance understanding of geo-hydro-bio-connections in calderas. Drillhole 1 targets a sub-vertical caldera margin zone (~500-800 m deep, deviated from vertical, temperature <120°C). Drillhole 2 targets intra-caldera volcanic deposits preceding the latest (c.a. 50 ka) major caldera-forming eruption (minimum 2 km deep, vertical). Existing multi-disciplinary caldera-scale datasets at the OVC support the delineation of promising sites to be discussed during the ICDP workshop. High-resolution geophysical imaging is ongoing at a promising caldera margin site. We have assembled a multi-disciplinary, diverse international science team. The project is informed by local Maori to integrate indigenous knowledge (Matauranga Maori) and approach to guardianship (kaitiakitanga) of the land. Regulatory authorities and emergency managers have contributed to the project design. The significant scientific discoveries will underpin 1) resilience to volcanic and seismic hazards; 2) sustainable management of groundwater and geothermal resources, and 3) understanding of subsurface microbial diversity, function and geobiological interactions. These topics are all potent for compelling education and outreach efforts, at Okataina and globally.

• CALDERA aims to resolve the spatio-temporal connections between magmatic, tectonic, hydrological, and microbial processes at caldera/rift intersections. Globally relevant questions are:
• 1) How do caldera magmatic plumbing systems and their eruptive behaviour mature and evolve?
• 2) How do complex crustal stresses vary in caldera regions and affect geo-hydro-bio-processes?
• 3) What controls fluid flow and chemistry in calderas?
• 4) What are the physicochemical conditions that drive subsurface microbial community structure, function and activity?
• 5) How to predict the onset and style of caldera unrest and eruptions? Petrologic, textural, geochemical and isotopic analysis, and dating of cores will provide a high-resolution record of eruption frequency and magnitude, magma compositions and storage conditions, and pre-eruptive processes. Crucially, drilling will provide records of small and old eruptions not exposed on the surface. Physical property and in-situ stress measurements on cores and downhole will quantify in-situ stress, reveal hydrothermal alteration processes, and calibrate geophysical models, to develop geomechanical and structural caldera models. Multi-scale fluid flow and composition measurements during drilling and monitoring will reveal groundwater-hydrothermal processes. Microbial communities will be assessed from cores and fluid samples in combination with geo-hydro-chemical drillhole data, and changes in volcanic/tectonic activity, to provide an unparalleled view of the underground ecosystem and its response to geologic activity. Extensive surface physicochemical and microbial community dataset will link biosphere and fluids from depth to surface.

Biosphere, Caldera, Hydrology, Magnetism, Tectonics

Latitude: -38.166667, Longitude: 176.5