Imaging Submarine Faulting, Hydrothermal Alteration, and Vent Structures Offshore Whakaari/White Island Using Surface-Towed Controlled Source Electromagnetics

Submarine hydrothermal vents associated with active volcanoes provide valuable insight into the shallow fluid migration pathways and volatile transport from magmatic systems. The distribution and activity of these vents are controlled by the subseafloor structure such as faulting and zones of hydrothermal alteration. These structural features govern fluid pathways and influence long-term volcanic behavior making the location, geometry, and variability of these structural and alteration features important information for volcanic hazard assessment. Additionally, hydrothermal vents provide sources of heat and chemically distinct substrates that support benthic ecosystems. Identifying and characterizing these features aids better understanding and management of these ecosystems.

Controlled-source electromagnetic (CSEM) methods are well suited for investigating these systems due to their sensitivity to changes in electrical resistivity associated with pore fluid composition and hydrothermal alteration. Here, we present results from a surface-towed CSEM survey conducted offshore Whakaari/White Island in the Taupō Volcanic Zone, New Zealand. The survey targeted regions containing previously mapped vent sites and was designed to image hydrothermal pathways within the upper few hundreds of meters of the seafloor. Additionally, survey lines extended from the island to the area surrounding Te Paepae o Aotea/Volkner Rocks, a site of inferred structural and magmatic connectivity, to capture active hydrothermal vent sites or shallow subseafloor alteration associated with prior venting activity.

Preliminary inversions reveal electrical resistivity signatures that we interpret as zones of volcanically altered material, fluid and/or gas flow along fault structures, and individual vent features. These results provide a detailed view of near-seafloor electrical structure associated with active and relict hydrothermal processes offshore Whakaari. Our inversions complement deeper constraints on magmatic systems from ocean-bottom EM surveys and regional airborne EM data by resolving shallow conductive and resistive features linked to fluid flow and alteration. These data improve characterization of shallow subsurface structure and hydrothermal pathways in an active volcanic setting and demonstrate the sensitivity of surface-towed CSEM to vent-related processes in the shallow seafloor.