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 to Jaluit. The civilian administration was established at Jabat Island and replaced the military administration in 1922. A small branch government office was established; and local Japanese settlers opened a small copra plantation on the island. In the early 1920s, a Japanese trader settled in Enewetak and made false claims that he had received permission from the government to develop coconut groves. The natives initially worked for the trader, but resisted after realising the trader's false claims. There was no permanent official at Enewetak and Ujelang, but a ship from Pohnpei would make occasional visits to the islands. Japanese traders