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
Geography of the Comoros The islands have a total land area of 2,236 square kilometers (including Mayotte), and claim territorial waters of 320 square kilometers. Mount Karthala (2316 m) on Grande Comore is an active volcano. From April 17 to 19, 2005, the volcano began spewing ash and gas, forcing as many as 10,000 people to flee. Comoros is located within the Somali plate. Geographic coordinates: Grande Comore is the largest island, sixty-seven kilometers long and twenty-seven kilometers wide, with a total area of 1,146 square kilometers. The most recently formed of the four islands in the archipelago, it is also of volcanic origin.