The collapse triggered tsunami waves that struck nearby and distant islands such as New Guinea, Umboi, Sakar and New Britain.

Ritter Island in the Bismarck Archipelago is an active stratovolcano located off the northeast coast of Papua New Guinea.

[2] Before the eruption of 1888, the island was described as a steep-sided and almost-circular volcanic cone and was a notable feature to sailors passing through the Dampier Strait.

[2] Based on sketches from the 1830s, the sides of the volcano had an average angle of 45°, with the western flank probably steeper as it had experienced minor landslides.

[3] An anonymous report stated that ashfall and tremors were recorded at Finschhafen in February 1887 and may have originated from Ritter Island.

These reports might suggest a magmatic eruption, however, an alternative explanation is a phreatic explosion caused by seawater entering the conduit system exposed by the landslide.

[3] The collapse was preceded by gradual, intermittent lateral spreading of the volcanic edifice, as evidenced by compressional structures in seismic profiles.

[1] Published in Marine and Petroleum Geology, a 2015 study estimated that Ritter Island lost 4.2 km3 (1.0 cu mi) of its volume by comparing a reconstructed topographic map of the volcano before and after its collapse.

This analysis revealed that the failure also involved part of the volcano’s base, which was constructed above weak marine sediments.

Tide gauges in Sydney, Australia, recorded abnormal readings ruled out as tidal floods and attributed it to a possible tsunami.

[10] Eighteen people; 2 Germans, 4 Malays, and 12 Melanesians from the Duke of York Islands, were on New Britain at the time as part of a New Guinea Company group surveying possible for coffee plantations areas.

The water level at the town was so low that it posed dangers to ships at the harbor, and a reef near Madang was exposed some 1.5–1.8 metres (5–6 ft).