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 occupation of the Andaman Islands Colonel Bucho, whilst a number of junior Indian officials in the administration were elevated to more responsible posts. The defence of the islands was assigned to the newly formed fighter squadron of the Kanoya Kōkūtai based at Tavoy in southern Burma. This fighter squadron was the former "Yamada Unit" under the control of the 22d Koku Sentai, then based at Penang. Six flying boats from the Toko Kōkūtai were dispatched on March 26, with twelve more arriving shortly thereafter. Within the islands a Japanese garrison of approximately 600 men, together with the police force, now under Japanese control, were responsible