Extent and Volume of Lava Flows Erupted at 9 degrees 50 ' N, East Pacific Rise in 2005-2006 From Autonomous Underwater Vehicle Surveys

Seafloor volcanic eruptions are difficult to directly observe due to lengthy eruption cycles and the remote location of mid-ocean ridges. Volcanic eruptions in 2005-2006 at 9 degrees 50 ' N on the East Pacific Rise have been well documented, but the lava volume and flow extent remain uncertain because of the limited near-bottom bathymetric data. We present near-bottom data collected during 19 autonomous underwater vehicle (AUV) Sentry dives at 9 degrees 50 ' N in 2018, 2019, and 2021. The resulting 1 m-resolution bathymetric grid and 20 cm-resolution sidescan sonar images cover 115 km(2), and span the entire area of the 2005-2006 eruptions, including an 8 km(2) pre-eruption survey collected with AUV ABE in 2001. Pre- and post-eruption surveys, combined with sidescan sonar images and seismo-acoustic impulsive events recorded during the eruptions, are used to quantify the lava flow extent and to estimate changes in seafloor depth caused by lava emplacement. During the 2005-2006 eruptions, lava flowed up to similar to 3 km away from the axial summit trough, covering an area of similar to 20.8 km(2); similar to 50% larger than previously thought. Where pre- and post-eruption surveys overlap, individual flow lobes can be resolved, confirming that lava thickness varies from similar to 1 to 10 m, and increases with distance from eruptive fissures. The resulting lava volume estimate indicates that similar to 57% of the melt extracted from the axial melt lens probably remained in the subsurface as dikes. These observations provide insights into recharge cycles in the subsurface magma system, and are a baseline for studying future eruptions at the 9 degrees 50 ' N area.