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 reportedly explored some of the nearby atolls before paying a visit to Labon Kabua, one of the principal chief in the Marshall Islands. Before Goto and Suzuki returned for Japan, they induced Kabua to raise the Japanese flag over his house at Ailinglaplap. The Japanese government subsequently ordered the two envoys to return to the island to haul down the flag upon the envoys' return. During the German colonial era, there were occasional reports of Japanese fishermen making landfalls in the atoll, and there was at least one other incident which Japanese fishermen were also killed by the islanders. A