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The Next Decade of Observations at Axial Seamount: A Geophysical Perspective
  • William Wilcock
William Wilcock
University of Washington

Corresponding Author:wilcock@uw.edu

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The Ocean Observatories Initiative Cabled Array (OOI-CA) is a 25-year facility that provides unprecedented power and communications at Axial Seamount and sites on the Cascadia continental margin. Although the OOI is sometimes viewed as too expensive, the CA provides two capabilities that would be infeasible in autonomous configurations. First, at the expense of a reduced number of instrument sites, it enables reliable long-term observations with suites of standard sensors. Second, it can support novel instrumentation with exacting power, bandwidth and real time requirements. At the summit of Axial Seamount, the core sensor network spans the southern half of the caldera, and comprises 7 seismometers, 2 hydrophones, 4 bottom pressure and tilt instruments, and a variety of sensors in two hydrothermal fields. Additional sensors have also been added for testing. The volcano erupted in April 2015, within months of the CA coming online, providing new insights into the workings of caldera ring faults and support for the inference that eruptions at Axial occur at predictable levels of inflation. As of Summer 2019, the volcano has recovered 70% of the deflation that occurred in 2015. Another eruption is expected in a few years and several more are quite possible over the lifetime of the system. Because Axial has a shallow magmatic system that is well imaged, it is an excellent setting to study the links between volcanism and caldera dynamics and search for signals that are precursory to eruptions at a variety of timescales. Such studies would benefit from temporary deployments of autonomous sensors timed to coincide with the predicted times of eruptions. The CA should also be used to address questions related to the formation of hydrothermal event plumes and their role in flushing out fluids and microbes from the subsurface. This will require the addition of one or more cabled moorings above the caldera and enhanced sampling capabilities. There is a proposal to install several instrumented boreholes at the summit of Axial Seamount that would employ the CA to support novel interactive microbial and hydrologic subseafloor experiments. The CA can also be used to test emerging technologies such as resident autonomous underwater vehicles and distributed acoustic sensing, which will provide new tools to address key scientific questions.