Relationships between lava types, seafloor morphology, and the occurrence of hydrothermal venting in the ASHES Vent Field of Axial Volcano

Deep-towed and submersible photographic surveys within the caldera of Axial Volcano have been integrated with high-resolution bathymetry to produce a geological map of the most active vent field (Axial Seamount Hydrothermal Expeditions (ASHES)) in the caldera. The ASHES vent field encompasses an approximately 200 m×1200 m area of active venting which is located adjacent to the southwest caldera wall. Locations for over 2000 photographs in and near the vent field were determined using a seafloor transponder network. Then each photograph was described utilizing a classification system which provides detailed information concerning lava type, hydrothermal activity, sediment cover, geological structure, and biology. Resulting data were entered into a digital data base, and computer-generated maps were created that portray spatial relationships between selected geological variables. In general, the entire ASHES field is characterized by pervasive low-temperature venting. The most vigorous venting is concentrated in an approximately 80 m×80 m area where there are several high-temperature vents including some which are producing high-temperature vapor-phase fluids derived from a boiling hydrothermal system. Lava types within the ASHES vent field are grouped into three distinct morphologies: (1) smooth (flat-surfaced, ropy, and whorled) sheet flows, (2) lobate flows, and (3) jumbled-sheet flows. The most intense hydrothermal venting is concentrated in the smooth sheet flows and the lobate flows. The location of the ASHES field is mainly attributable to faulting which defines the southwest caldera wall, but the concentration of intense venting appears to be related also to the spatial distribution of lava types in the vent field and their contrasting permeabilities. Other structural trends of faults and fissures within the field also influence the location of individual vents.