Ritter volcano is a very active basaltic-andesitic stratovolcano and forms the Ritter Island between Umboi and Sakar Islands in the Dampier Strait., ca. 9.5 km NE of Umboi Island and 21 km west of New Britain.
Present-day Ritter Island is the remnant of a larger island which was destroyed during a massive flank collapse in 1888, which reduced the near circular steep and 780 m high original volcanic island to to a small 140 m high and 1900 m long arcuate island with a steep west-facing cliff that continues below sea level. Devastating tsunamis were produced by the 1888 collapse and swept onto the coast of Papua New Guinea and offshore islands.
Many eruptions from Ritter Island are submarine. Along with the landslides that often accompany them, they frequently generate tsunamis.