Deformation Monitoring and the Magmatic Cycle at Axial Seamount, NE Pacific

Abstract:

Axial Seamount is the most active submarine volcano in the NE Pacific and is now the best monitored submarine volcano in the world with the recent addition of a cabled observatory by the US Ocean Observatories Initiative (OOI). Axial is a basaltic hot spot volcano superimposed on the Juan de Fuca spreading ridge, giving it a robust magma supply. It had effusive eruptions in 1998, 2011, and 2015. Deformation measurements have been conducted at Axial Seamount since the late 1980’s with precise pressure sensors that can detect vertical movements of the seafloor. This monitoring became more systematic after 2000, producing a time-series of inflation and deflation that can be used to model deformation sources and constrain the magma supply rate over time. Improved seafloor deformation measurements between 2011 and 2015 documented a four-fold increase in magma supply and confirmed that Axial Seamount’s eruptive behavior is inflation-predictable, probably triggered by a critical level of magmatic pressure. The 2015 eruption was successfully forecast based on this deformation pattern and was the first time that deflation and tiltmeter data were captured in real-time by the new seafloor cabled observatory, revealing the timing, location, and volume of eruption-related magma movements. Improved modeling of the deformation suggests a steeply dipping prolate-spheroid pressure source beneath the eastern caldera that is consistent with the location of the highest melt zone within the sub-caldera magma reservoir determined from multi-channel seismic results.