Topographic and geomorphological features of a hydrothermal field in submarine Mienhua Volcano offshore northeastern Taiwan

There is a high potential of hydrothermal mineral deposits in the Southern Okinawa Trough offshore northeastern Taiwan. This study aims to integrate bathymetry data, water column images, seabed image, sub-bottom profiles and ROV observations to better understand a hydrothermal field, submarine Mienhua Volcano (MHV). A repeated mapping survey equipped with EM-712 was conducted to see if significant bathymetric changes took place since 50 days in MHV. The volcano of 2 km width and 240-m relief height is present at about 1300-m water depth near Mienhua Canyon. The volcano combines with several small and rugged mounds. From ROV observations, two of the mounds show active hydrothermal vents covered by white tubeworms and a white smoker with some mussels, respectively. In addition, active water column gas flares are observed on the southeastern part of MHV. Based on the identification of sub-bottom profiles, the special distribution of acoustic blanking zone shows the southeastern part is more narrow than the northwestern area. However, comparing the bathymetry mapped in two times, no obvious overall morphological changes are detected, except on the volcano rim. Seabed image also reveals similar backscatter intensity within the rugged mounds, suggested they may be at similar stages of morphological development. We consider that the hydrothermal vents are variable. In addition, the preliminary results indicate the fluid migration is the important process to influence the evolution of the hydrothermal field in MHV. Therefore, we also applied more seafloor images, geochemical and geophysical data which have been reported in MHV. Our results could evaluate the relationship between the flare activities, geomorphological features and the location of the blanking zone in the sedimentary strata.