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 closer cultural and economic ties with Japan. Japanese firms that were based on the Marshall Islands since the 1960s actively sought joint ventures with local companies from the 1980s onwards, mainly in the fishery sector. Expatriates usually consisted of Okinawan fishermen based at Majuro, where Japanese companies have built smoking and canning facilities to facilitate the processing of tuna catches. The Marshall Islands remained sparsely populated by Japanese settlers, relative to the other mandated Micronesian islands. The first pre-war census of the Marshall Islands counted 490 Japanese among 10,000 Marshallese, and the number of Japanese settlers increased to 680 scattered