Northern Mariana Islands, also called Northern Marianas, officially Commonwealth of the Northern Mariana Islands, a self-governing commonwealth in association with the United States. It is composed of 22 islands and islets in the western Pacific Ocean. The commonwealth is a part of the Mariana Islands, a chain of volcanic mountain peaks and uplifted coral reefs. (The Marianas chain also includes the politically separate island of Guam, to the south.) Saipan (46.5 square miles [120 square km]),Tinian (39 square miles [101 square km]), and Rota (33 square miles [85 square km]) are the principal islands and, together with Anatahan, Alamagan, and Agrihan, are inhabited. Another island, Pagan, was evacuated in 1981 after a severe volcanic eruption there. The capital is on Saipan.
Rota, the southernmost island, consists of a volcanic base capped with coral limestone, giving it a terraced appearance. Four southern islands (Farallon de Medinilla, Saipan, Tinian, and Aguijan) are composed of limestone and have gently rolling elevations and few mountains. The islands farther north are volcanic peaks.Mount Pagan, one of the two volcanoes that make up Pagan Island, has erupted many times during recorded history; Farallon de Pajaros, the northernmost of the Marianas, and Asuncion are also active volcanoes. Agrihan volcano, the highest of the Northern Mariana group, rises to 3,166 feet (965 metres). Besides Guam, the nearest neighbours are the Bonin Islands (north) and the Federated States of Micronesia (Caroline Islands; southeast).