ACTIVITY OF THE YAKATABARI MUDSLIDE COMPLEX, PORGERA, PAPUA-NEW-GUINEA

The Yakatabari mudslide complex, formed on overconsolidated mudrocks i n Enga Province, Papua New Guinea, has a volume of about 16 x 10(6) 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 phi(p)' = 24.5-degrees and c(p)' = 11 kPa. Simple models using the infinite slope stability assumption s suggest a probability of failure of approximately 22%. Several histo ric 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 fines. Prehistoric failures are indicated by arcuate scarps across the complex. Twenty C-14 dates from the mudslide indicate a fai lure history spanning more than 40,000 years. The Yakatabari mudslide complex appears to be a very long-lived landslide. Landslides of simil ar longevity appear to have not been described in the literature but i t is unlikely that the Yakatabari example is unique.