Supply Reef is a submerged circular reef of volcanic origin in the Northern Mariana Islands chain, about NW of the Maug Islands. Presently, this igneous seamount is roughly below the ocean's surface and about in diameter. Apparent episodes of submarine volcanism were noted on December 22âÂÂ24 and 26âÂÂ27 in 1989.
Volcanic and seismic activity has been noted, as well as hard and soft corals.