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 air attacks on the Mariana Islands the operation was not called off after this raid, it did not go ahead after the Japanese surrender on 15 August. The Japanese military also developed a plan to attack Saipan using Mitsubishi Ki-167 suicide aircraft during August, but nothing came of this. The Japanese attacks on the Mariana Islands during 1944 and 1945 did not seriously disrupt the USAAF's strategic air campaign against Japan. They did, however, force the United States to allocate forces to defend the islands in order to prevent further losses of expensive B-29s. Moreover, due to the high cost of the heavy bombers, the ratio