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
South Georgia and the South Sandwich Islands groups, while the southernmost make up Southern Thule. The three largest islandsSaunders, Montagu, and Bristollie between the two. The Islands' highest point is Mount Belinda () on Montagu Island. The South Sandwich Islands are uninhabited, though a permanently manned Argentine research station was located on Thule Island from 1976 to 1982 (for details, see above). Automatic weather stations are on Thule Island and Zavodovski. To the northwest of Zavodovski Island is the Protector Shoal, a submarine volcano. The South Sandwich Islands from north to south are: A series of six passages separates each of the islands or island groups in