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 Federated States of Micronesia and Palau. The German authorities chased out most of the businessmen in 1900, leaving only a few Japanese in the Micronesian islands. A few Japanese began settling in the islands in 1907 after the German authorities allowed the Japanese traders to establish their enterprises in Pohnpei and Chuuk. Early Japanese settlers consisted of single men, and official statistics showed a gender imbalance with five Japanese males to one female. Many Japanese men took on Micronesian wives and raised mixed Japanese–Micronesian families. Japanese arrivals to Micronesia remained modest until the 1920s, following which the islands experienced a quick increase in the