What was the primary cause of the 1998 Papua New Guinea tsunami?

The primary cause of the 1998 Papua New Guinea tsunami was a submarine landslide. The landslide was triggered by a large offshore earthquake near the northern coast, close to the town of Aitape, on 17 July 1998.

Scientists initially believed that the earthquake itself had displaced the seafloor enough to produce the tsunami. However, the tsunami was much larger than expected from the earthquake’s size and local seafloor evidence indicated that a massive underwater slope failure had moved a great volume of water.

The event became an important warning for tsunami science: a moderate earthquake can generate a devastating tsunami if it causes an underwater landslide. More than 2,000 people died, and some coastal communities were struck with little warning.