ABSTRACT

This research project continues long-term study and monitoring of the most active submarine volcano in the world. Axial Seamount is located about 300 miles off the coast of Oregon and represents one of the best places to study how volcanoes work because it erupts frequently and repetitively and has numerous monitoring instruments linked to shore via cable which is part of the newly commissioned National Science Foundation's Ocean Observing Initiative. This research focuses on continuing the present time series data collection effort and using the data to understand how magma (molten rock) is stored in the shallow crust at volcanoes, how it is delivered to the surface, how eruptions are triggered, and how eruptions can be successfully forecast. Field work involves use of newly developed, precise, pressure sensors and autonomous underwater vehicles using geodetics to measure vertical movements of the seafloor, which take place as Axial Seamount, gradually inflates like a balloon, with magma seeping in and filling its subterranean magma chamber a few kilometers below the seafloor. During inflation (the present situation) and deflation (loss of volume due to eruption of lavas on the seafloor, the last of which occurred in 2015) the seafloor moves up and down as much as 8-12 feet. As observed in Axial's last two eruption cycles, when the volcano is fully "re-inflated" it is ready to erupt again. Monitoring for almost two decades has shown that Axial Seamount inflates to a similar amount before each eruption. This allowed the two previous eruptions to be successfully forecast months in advance. Collection of this new data will be complemented by geodynamic modeling focused on understanding how volcano inflation influences the deformation field around it. Broader impacts of this research have broad implications for the understanding of volcano hazards, utilizes the new Ocean Observing Initiative's cabled array and complementary sensor suites, helps build infrastructure for science, and provides training for students. It will also result in a new software package to enable autonomous underwater vehicles to perform terrain-following grids of features on the seafloor. Results from this study may have important implications for better understanding magma chamber filling and eruption associated with volcanoes on land where the continental crust, many times, adds complexity to fundamental magma generation and magma chamber filling processes.

Axial Seamount is on the Juan de Fuca Ridge off the coast of the northwestern United States. It erupted in 1998, 2011, and most recently again in April 2015. It has been instrumented for this period of time with sensors that can detect ground motion and changes in elevation over time. It is now hooked to the undersea data cable and junction box of the National Science Foundation's Ocean Observing Initiative's cabled array. Thus, Axial Seamount is an ideal natural laboratory for the long-term study of active processes of submarine volcanos in a mid-ocean ridge setting. Long-term research and monitoring of Axial has created a remarkable time-series dataset of bottom pressure observations that have revealed repeated cycles of inflation and deflation that have been used to forecast eruptions with increasing accuracy. The 2015 eruption was the first captured in real time by the network of sensors now installed inside the volcano's caldera and on its flanks. These installations have revealed the inner workings of the volcano in unprecedented detail. This research will follow up on recent work by using autonomous underwater vehicles that generate high-resolution bathymetric maps that show the Axial deformation field extends well beyond its summit caldera. These new data complement the continuous, but spatially limited, pressure sensor measurements and put them into a geologic, morphological framework. This research will continue the pressure measurements and further develop a new autonomous underwater vehicle navigation technique to improve seafloor survey reliability and reproducibility. Results of this will be used to advance modeling of the deformation of the Axial subsurface magmatic system. It will also explore new quantitative numerical methods for improving eruption forecasts.

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