The merged island lies some 1,000km (621mi) south of Tokyo, the result of eruptions on the seafloor that have spewed enough material to rise above the water line.
In November 2013, a new island sprouted near to Nishino-shima, another volcanic landmass that last expanded in the 70s.
Four months later, the new and old islands are one island.
The newer portion of the island – which was referred to as Niijima – is now larger than the original Nishino-shima landmass.
The merged island is slightly more than 1km (3,280ft) across.
According to Nasa, two cones have formed around the main volcanic vents and stand more than 60m above sea level.
Volcanic lava flows are reported to be most active now on the south end of the island.
The new landmass lies in the Ogasawara (Bonin) Island chain.