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
Battle of the Treasury Islands the operation, the New Zealand 8th Infantry Brigade Group, commanded by Brigadier Robert Row and part of the New Zealand 3rd Division, was assigned to the United States' III Amphibious Force, which assigned its Southern Force under Rear Admiral George H. Fort for the operation. Consisting of two islands, Mono and Stirling, the Treasuries are located north of Guadalcanal, and from Vella Lavella, and just from the Shortland Islands. At the time of the battle, the islands offered the Allies further opportunities to bypass large groups of Japanese forces as they advanced through the Solomons towards the main Japanese base