Abstract

The landslide at Kaiapit occurred on the morning of 6 September 1988 in the Finisterre Range of Papua New Guinea and resulted in 74 fatalities. The landslide involved an estimated 2 km3 of debris which covered an area of 11.4 km2 and left a back-scarp some 1600 m high. The debris ran out in three flows for approximately 6 km in 5 minutes and velocities of 180km/h have been estimated. No single cause for the initiation of the landslide has been determined. It is felt that its location in a tectonically and seismically active region, the tropical climate and an inherently weak rock mass were fundamental contributary factors. The failure mechanisms are considered to have been massive planar slides. The debris assumed a final angle of rest of 6°; this may be explained by a combination of the concepts of acoustic fluidization and air entrapment. The landslide debris resulted in the formation of four dams, which had all breached within eight months of the event. Active erosion of the debris is resulting in the aggrading of river bed levels in the area.

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