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 Northern Mariana Islands Geography of the Northern Mariana Islands This article is about the geography of the Northern Mariana Islands. The Northern Mariana Islands, together with Guam to the south, compose the Mariana Islands. The southern islands are limestone, with level terraces and fringing coral reefs. The northern islands are volcanic, with active volcanoes on Anatahan, Pagan and Agrihan. The volcano on Agrihan has the highest elevation at . About one-fifth of the land is arable; another tenth is pasture. The primary natural resource is fish, some of which are endangered species, which leads to conflict. Also, development has created landfills which have