The Marshall Islands sit atop ancient submerged volcanoes rising from the ocean floor, about halfway between Hawaii and Australia, north of Nauru and Kiribati, east of the Federated States of Micronesia, and south of the disputed U.S. territory of Wake Island, to which it also lays claim. The atolls and islands form two groups: the Ratak (sunrise) and the Ralik (sunset). The two island chains lie approximately parallel to one another, running northwest to southeast, comprising about  of ocean but only about  of land mass. Each includes 15 to 18 islands and atolls. The country consists of a total of 29 atolls and five individual islands situated in about  of the Pacific. The largest atoll with a land area of  is Kwajalein. It surrounds a  lagoon.