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 archipelago the archipelago from Japan's colonies and other territories in the first half of the 20th century. The archipelago consists of 6,852 islands (here defined as land more than 100 m in circumference), of which 430 are inhabited. The four main islands, from north to south, are Hokkaido, Honshu, Shikoku, and Kyushu; Honshu is the largest and referred to as the Japanese mainland. The current Japanese archipelago topography is: Japanese archipelago The is a group of 6,852 islands that form the country of Japan. It extends over from the Sea of Okhotsk northeast to the Philippine Sea south along the northeastern