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
McDonald Islands (volcano) of the islands, at around in area. It has been the main focus of activity in recent times. Prior to 1996, McDonald Island had been a flat green island whose pumice beaches provided a great nesting area for penguin breeding. The island now has two main peaks, Maxwell Hill and Samarang Hill – the highest is Maxwell Hill at . Prior to 1992, no eruptions had taken place at the McDonald Islands volcano for 75,000 years. A series of eruptions started in 1992. The first recorded eruption from the McDonalds was from a submarine vent (a small VEI-0 eruption) in