A large atoll formation of northern Chuuk State, Nomwin is located 9 km southwest from Murilo, 36 km east from the small island of Fayu and 82 km north from Chuuk.

Hemispherical in shape, Nomwin has maximum dimensions of 30 km in length (along the southeastern rim) and 18 km in width (across the central regions, southeast to northwest). The atoll represents the emergent southwestern summit of a large, twin-lobed seamount — the atoll of Murilo emerges from the northeastern summit of the same seamount.

The deep central lagoon (52 m) is enclosed by an outer reef rim that is broken by wide passages into seven major segments and several smaller reefs. The largest islets are found on the reefs of the southeastern face of the atoll; two tiny islets on the western side of the atoll are the only islands found to be found elsewhere on the rim. The islets have a combined land area of 1.8 km².

image: millenium coral reefs landsat archive/usf millenium global coral reef mapping project/nasa seawifs/nasa jsc