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
Poor Knights Islands or, that the islands were named for their resemblance to Poor Knight's Pudding, a bread-based dish topped with egg and fried, popular at the time of discovery by Europeans. The chain consists of two large islands (Tawhiti Rahi, the larger at , and Aorangi () to the south), and several smaller islands. Aorangaia and Archway Island lie to the southwest of Aorangi Island, and there is also a group of smaller rocky islets between the two main islands, the largest of which is Motu Kapiti. The Poor Knights Islands are the eroded remnants of a 4-million-year-old rhyolitic volcano that is