Activity of the Yakatabari mudslide complex, Porgera, Papua New Guinea

The Yakatabari mudslide complex, formed on overconsolidated mudrocks in Enga Province, Papua New Guinea, has a volume of about 16 × 10⁶ m³. Detailed examination during 17 years as part of a mining development indicates a variety of colluvium types with variable properties, but average peak shear strength values of φ′_p = 24.5° and c_p′ = 11 kPa. Simple models using the infinite slope stability assumptions suggest a probability of failure of ∼ 22%. Several historic failures have occurred within the mudslide complex since 1974 and rates of movement of 40-240 mm/month have been documented on a number of survey lines. Prehistoric failures are indicated by arcuate scarps across the complex. Twenty ¹⁴C dates from the mudslide indicate a failure history spanning more than 40,000 years. The Yakatabari mudslide complex appears to be a very long-lived landslide. Landslides of similar longevity appear to have not been described in the literature but it is unlikely that the Yakatabari example is unique.