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Volcanic and Hydrothermal Activity of the North Su Volcano: New Insights from Repeated Bathymetric Surveys and ROV Observations.

Control ID: 1794263

Title: Volcanic and Hydrothermal Activity of the North Su Volcano: New Insights from Repeated Bathymetric Surveys and ROV Observations.

Authors (First Name, Last Name): Janis Thal1, Wolfgang Bach1, Maurice Tivey2, Dana Yoerger2

Institutions (All):

  1. University Bremen/MARUM, Bremen, Bremen, Germany.
  2. Woods Hole Oceanographic Institution, Woods Hole, MA, United States.

Abstract Body: Bathymetric data from cruises in 2002, 2006, and 2011 were combined and compared to determine the evolution of volcanic activity, seafloor structures, erosional features and to identify and document the distribution of hydrothermal vents on North Su volcano, SuSu Knolls, eastern Manus Basin (Papua New Guinea). Geologic mapping based on ROV observations from 2006 (WHOI Jason-2) and 2011 (MARUM Quest-4000) combined with repeated bathymetric surveys from 2002 and 2011 are used to identify morphologic features on the slopes of North Su and to track temporal changes. ROV MARUM Quest-4000 bathymetry was used to develop a 10 m grid of the top of North Su to precisely depict recent changes. In 2006, the south slope of North Su was steeply sloped and featured numerous white smoker vents discharging acid sulfate waters. These vents were covered by several tens of meters of sand- to gravel-sized volcanic material in 2011. The growth of this new cone changed the bathymetry of the south flank of North Su up to ~50 m and emplaced ~0.014 km3 of clastic volcanic material. This material is primarily comprised of fractured altered dacite and massive fresh dacite as well as crystals of opx, cpx, olivine and plagioclase. There is no evidence for pyroclastic fragmentation, so we hypothesize that the fragmentation is likely related to hydrothermal explosions. Hydrothermal activity varies over a short (~50 m) lateral distance from “flashing” black smokers to acidic white smoker vents. Within 2 weeks of observation time in 2011, the white smoker vents varied markedly in activity suggesting a highly episodic hydrothermal system. Based on ROV video recordings, we identified steeply sloping (up to 30°) slopes exposing pillars and walls of hydrothermal cemented volcaniclastic material representing former fluid upflow zones. These features show that hydrothermal activity has increased slope stability as hydrothermal cementation has prevented slope collapse. Additionally, in some places, hydrothermal crusts cover loose volcaniclastic material on the steep slopes and stabilize them.

Keywords: 3045 MARINE GEOLOGY AND GEOPHYSICS Seafloor morphology, geology, and geophysics, 3017 MARINE GEOLOGY AND GEOPHYSICS Hydrothermal systems, 8427 VOLCANOLOGY Subaqueous volcanism.