Quantification of eruption dynamics on the north rift at Axial Seamount, Juan de Fuca Ridge

Key Points: AUV mapping along the north rift identifies hummocky mounds with pillows, channelized, and inflated flows formed during the 2015 eruption. Impulsive sounds formed by lava/seawater interaction track mound growth over a 28 day period with an average extrusion rate of 22-45 m3s-1. The sounds record the history of flow advancement and inflation from multiple eruptive centers, and is used to infer volcanic activity style. Quantifying eruption dynamics in submarine environments is challenging. During the 2015 eruption of Axial Seamount, the formation of hummocky mounds along the north rift was accompanied by tens‐of‐thousands of impulsive acoustic signals generated by the interaction of lava and seawater. A catalog of these sounds was integrated with detailed seafloor mapping to better understand eruptive processes in time and space. Mounds grew over a period of 28 days with average extrusion rates of 22 to 45 m3s‐1. The most distant mounds, ~ 9.5 to 15.5 km down rift from the caldera, grew primarily over the first few days of the eruption. The focus of eruptive activity then retreated ~5 km toward the caldera where it was sustained. Mounds are constructed as a series of superimposed lobes formed through alternating periods of flow inflation, generating up to 30‐m‐thick hummocks, and periods of flow advancement, with