Spanning roughly 8 by 14 km (5 by 9 mi), the caldera is flooded by Blanche Bay.
The largely submerged caldera long formed a natural harbor for what had been New Britain's largest city, but a major eruption forced the evacuation of Rabaul City in 1994.
This image shows a diffuse white vapor plume extending west-southwest from the summit. Numerous volcanoes contribute to the landmass of the island of New Britain, the largest in the Bismarck Archipelago of Papua New Guinea.
One of the most active of these volcanoes - Ulawun - is also the tallest, with a summit elevation of 2,334 m (7,657 ft).
While Ulawun has been active since at least 1700, the most recent activity at Bamus occurred in the late 19th century.
A large region of ocean surface highlighted by sunglint - sunlight reflecting off the water surface - is visible to the north-northeast of Ulawun. Volcanic cones and settlements mingle along the margins of the Rabaul Caldera on the northeastern tip of Papua New Guinea's New Britain Island.
Occasional pyroclastic flows of rock fragments and volcanic ash have also occurred.
Shaped like a giant cauldron, the caldera is the remaining rim of an ancient volcano.
Small volcanic cones, some of which are still active, sit on the rim.
This astronaut photograph shows a plume of white steam and ash extending from the summit crater of the stratovolcano towards the northwest.
The plume begins to broaden as it passes the southwestern coast of Lolobau Island, approximately 23 km downwind. Ulawun is also known as "the Father," with the Bamus volcano to the southwest also known as "the South Son." The summit of Bamus is obscured by white cumulus clouds (not of volcanic origin) in this image.