The small circular island at the top-center is Sakar, the NE-most of a chain of volcanic islands off the northern coast of Papua New Guinea. The 8 x 10 km wide island, seen in this Space Shuttle image with north to the upper left, is an incised stratovolcano with a summit crater lake. The 50-km-wide island of Umboi, whose left side is cut by a large caldera breached to the NE, fills the center of the image.

NASA Space Shuttle image STS50-100-D, 1992 (http://eol.jsc.nasa.gov/).

This image is made available as a Public Domain Work, but proper attribution is appreciated.

Umboi

Sakar