The research vessel SONNE departed Yokohama for expedition SO320/1 to the Hess Rise, a vast and little-studied volcanic plateau in the North Pacific between Japan and Canada. The T-shaped feature stretches roughly 1,000 kilometers and has seen few scientific visits because of its remote location. The previous expedition occurred in 1980. German and Japanese teams have renewed focus on the area over the past two years. The current cruise, led by GEOMAR, will test models of how the plateau formed on its western and northern sections. A follow-up cruise, SO320/2, will continue the work. Expedition leader Dr. Anke Dannowski noted that eight days at sea are allocated just for transit. Oceanic plateaus arise from repeated massive lava flows that stack over time, with individual flows extending hundreds of kilometers and reaching tens to hundreds of meters thick. Intense volcanism during the middle Cretaceous, 115 to 90 million years ago, produced at least twelve major plateaus worldwide. Three formation models will be examined: development along a migrating triple junction of tectonic plates, formation at the former Pacific-Farallon spreading center, or creation as an intraplate feature above a mantle plume. Researchers will also check whether the same hotspot earlier produced the nearby Shatsky Rise about 30 million years before renewed activity at Hess Rise. Up to 40 ocean-bottom seismometers will be placed on the seafloor between 2,000 and 5,000 meters depth to record movements and pressure waves. Additional data will come from shipboard gravity measurements, a towed magnetometer, and multibeam seafloor mapping. The resulting information will reveal the plateau’s composition and internal structure. The next cruise will gather rock samples for age dating, allowing integration of geophysical and geological findings. Before departure, scientists from both nations met at a German Embassy reception in Yokohama. The group later visited JAMSTEC in Yokosuka and its vessel KAIMEI, and students from the German School Tokyo/Yokohama toured the SONNE.
