Extent of Submarine Volcanic Plume Deposition Offshore Olosega Island in American Samoa

Abstract

There has been little mapping of the seafloor, resulting in a large lack of knowledge of seafloor environments. It is important to map the seafloor for numerous reasons, such as being able to predict and mitigate public risk from tsunamis caused by faulting, determining what habitat locations are best to anchor alternative energy infrastructure, and monitoring the health of organisms and their habitats on the seafloor. In order to get a better understanding of the impact of volcanic submarine sediment on seafloor environments, we mapped and collected sediments at an 1866 eruption site between the Manu’a Islands in American Samoa. The goal of this research is to get a first look at the post-eruption bathymetry, evaluate where the volcanic sediment settled, determine the size and type of the volcanic sediment, and assess how the bathymetry of the seafloor changed from the eruption. This data was collected on a 14-day cruise on the R/V Thompson in American Samoa and used a multibeam sonar system to map the seafloor bathymetry and a grab sampler to take sediment samples. Eight volcanic sediment samples were collected and processed. These comprised of sand and gravel sized (400-4300 μm) fragments of volcanic origination. We were not able to say that the grain size data showed a strong correlation with distance from the eruption site and backscatter, as we only could process seven sediment samples and were unable to date them to the eruption. We were able to map the eruption site and the surrounding seabed, finding evidence of other geological processes such as landslides and more volcanoes. This data gives us greater insight into the settling processes after an eruption and helps us predict future effects and impacts from submarine eruptions.