Bonin Islands Pacific Plate is subducting under the Philippine Sea Plate, which creates an oceanic trench to the east of the islands: the Bonin Trench. The crust of the Ogasawara Islands was formed by volcanic activity when subduction began 45–50 million years ago, and is composed mostly of an andesitic volcanic rock called boninite, which is rich in magnesium oxide, chromium, and silicon dioxide. The Ogasawara Islands may represent the exposed parts of an ophiolite that has not yet been emplaced on oceanic crust. The rocks of the Volcano Islands are much younger; Iwo Jima is a dormant volcano characterized by rapid
Japanese settlement in the Marshall Islands on a Burns Philp steamer noted that the most Marshallese women wore the kimono instead of the traditional loincloth ("lavalava" in Marshallese) in October 1918. Interethnic relations between the Japanese settlers and civil servants with the Marshallese were friendly, but racial segregation was enforced between Japanese and Micronesians in the workforce and educational sectors. As compared to Micronesians from other islands, Marshallese generally retained more aspects of their traditional lifestyles, relative to the small Japanese populace in the islands. Contrary to Japanese settlements in the other mandated islands, settlers consisted mainly of single men, and intermarriages with Marshallese women were