 
East New Britain, Papua New Guinea
4.12 S , 152.2 E
  
  submarine volcano
  
  Caldera 
Tavui caldera is located offshore from east New Britain, Papua New Guinea. Its impressive formation can be seen as a spectacular 1000m drop-off at a location called submarime base.

  Tavui Caldera wall - John Seach
Further reading
  McKee, C.O., 2015. Tavui Volcano: neighbour of Rabaul and likely source of the Middle Holocene penultimate major eruption in the Rabaul area. Bulletin of Volcanology, 77(9), p.80.
Possible Holocene eruptions of Tavui Volcano.