Final answer:
The anomalously large tsunami in Papua New Guinea in 1998 was caused by an earthquake and landslide.
Step-by-step explanation:
A tsunami is a series of sea waves caused by an underwater earthquake, landslide, or volcanic eruption.
In the case of the anomalously large tsunami in Papua New Guinea in 1998, the cause was a combination of an earthquake and a landslide. At 8:32 a.m. on May 18, an earthquake triggered a gigantic landslide on the unstable north flank, which in turn created the massive tsunami.