The Cabled Observatory Vent Imaging Sonar, otherwise known as COVIS, has acquired several months of plume centerlines and strengths for several vents in the ASHES vent field of Axial Seamount. COVIS was initially installed at ASHES vent field in July 2018 and acquired imaging data throughout July-September 2018 and since July 2019. COVIS uses acoustic imaging to monitor the strength and behavior of the plumes formed above black smokers and diffuse discharge sites in an approximately 40 m by 40 m region which includes Inferno and Mushroom vents. Preliminary observations suggest that the plumes above Inferno are highly variable; sometimes a distinct rising column is seen to expand with height while other times there is little acoustic evidence for a plume at all. Potential explanations range from variable discharge rates to variable discharge salinity driving collapsing plumes to extremes in bottom currents. The obvious simple explanation of bent plumes produced by extreme bottom currents is unsatisfactory as such bent (even horizontal) plumes should be visible in the acoustic imaging data. Initial explorations of the impact of near seawater salinity variations suggest this is a plausible explanation for variations in plume maximum height independent of heat content. However, the paucity of recent or continuous salinity and temperature sampling on Inferno limits the certainty of interpretations suggesting variations in venting. In contrast to the variable plumes, the sulfide mounds of the region (Inferno, Mushroom, Hell and Phoenix) appear as consistent (stable) silhouettes in the acoustic images. On Inferno, we can even see indications of the thin chimneys on top of the mound from which primary venting occurs. Preliminary work is focused on refining the classification of acoustic returns between rock, sulfide, and water to see if we can track the growth (and collapse) of the actively venting chimneys.
