Development of an early warning system for shallow landslide hazard in the Grasberg area, Indonesia

In the middle of the 20th century, one of the largest open pit mining facilities in the world was established at Grasberg on top of the main Papuan ridge. In time, this expanded to become the most notable man-made landscape feature on the entire island. Mining operations are supported by a large array of workshops and facilities, scattered from the top of the mountain down to the seashore. They include large camps and mining villages hosting the workforce and their families. In this work, we present the results of a project to help mining company staff define triggers for an early warning system (EWS) for shallow landslides using meteorological forecasts and rain gauge measurements. This would help to mitigate the risk for the Grasberg mine and surrounding valleys of sudden detachment, routing and runout of shallow landslides. To achieve such a scope, the work has been split into three main tasks: Definition of rainfall thresholds for the initiation of shallow landslides in the broader Grasberg area based on cumulative rainfall thresholds (CRT) and intensity-duration thresholds (IDT). Development of a hazard map for shallow landslides, including predictions of initial location, runout and volumes of sediment involved using a state-of-the-art machine learning multivariate statistical analysis tool called Random Forests (RF). Setup of an EWS based on the rainfall thresholds and support for the implementation of the operational chain of risk mitigation routine procedures already in place.