Award: OCE-1546616

The main goal of this project was a rapid response to the volcanic eruption at Axial Seamount that started on 24 April 2015. The NSF-funded Ocean Observatories Initiative?s (OOI) Cabled Array monitoring network detected the eruption, heralded by a swarm of >8000 earthquakes and a rapid subsidence of the seafloor by >2.4 meters at the center of the caldera. Rapid response activities enable the study of key processes that are poorly understood and require timely measurements to advance our knowledge and will not be possible later. This award supported research activities during 3 extra days at sea that were added to a previously scheduled research expedition on R/V Thompson (TN327). The research cruise made dives at Axial Seamount with the Jason ROV and Sentry AUV, during August 14-29, 2015. Operations included mapping and sampling of the new lava flows, sampling of new hydrothermal vents on the new flows, CTD casts and tows of hydrothermal plumes over the new lavas, deployment and recovery of monitoring instruments and moorings, and continuing long-term measurements of the cycle of inflation and deflation at the volcano. The rock samples we collected show that 2015 lava flows have the most mafic composition erupted in the last 600 years at Axial Seamount, probably a consequence of the four-fold increase in magma supply rate documented by the inflation/deflation time-series measurements since 2011. CTD casts and tows documented and sampled hydrothermal plumes over the 2015 lava flows on the north rift zone, which varied significantly in character along the length of the rift. The Jason ROV dives also documented small explosion pits in the 2015 lava flows that could be related to the impulsive signals detected by the OOI Cabled Array seismometers during the eruption. Sentry AUV dives mapped some of the 2015 lava flows in high resolution and helped discover some previously unknown eruptive centers on the north rim of the caldera. The outcomes from this project include a cruise web site (http://axial2015.blogspot.com/), as well as these papers published in scientific journals: Chadwick, W. W., Jr., B. P. Paduan, D. A. Clague, B. M. Dreyer, S. G. Merle, A. M. Bobbitt, D. W. Caress, B. Philip, D. S. Kelley, and S. L. Nooner (2016), Voluminous eruption from a zoned magma body after an increase in supply rate at Axial Seamount, Geophys. Res. Lett., 43, 12,063–012,070, doi:10.1002/2016GL071327. Nooner, S. L., and W. W. Chadwick, Jr. (2016), Inflation-predictable behavior and co-eruption deformation at Axial Seamount, Science, 354(6318), 1399-1403, doi:10.1126/science.aah4666. Last Modified: 07/27/2017 Submitted by: William W Chadwick