The Parraguirre ice-rock avalanche 1987, semi-arid Andes, Chile - A holistic revision

On November 29 in 1987, a massive ice-rock avalanche detached near Cerro Rubicano in the Dry Andes east of Santiago de Chile. The avalanche developed into a highly destructive debris flow, which reached a run-out distance of more than 50 km resulting in important damage of infrastructure and causing numerous fatalities. In the wake of the event, several studies have shed light on the event history as well as on the geological, volcano-seismic, meteorological and glacio-hydrological pre-conditioning. Although the El-Niño event, that prevailed in 1987, and the presence of glaciers are considered important factors for the development of such a massive debris flow, a holistic analysis of observational evidence, meteorological conditions and debris-flow simulations remains, to this day, absent.

Here, we present new insights obtained from historic aerial photographs and satellite imagery, climate reanalysis, weather stations, hydrographic monitoring and physically-based debris-flow modelling. First, we are able to better constrain the trigger volume and to delineate a first map of the impact area. Second, time records and modelling results affirm the assumed multi-stage character of the event. Third, we postulate that the Parraguirre event can be considered a compound weather event, pre-conditioned by anomalously high temperatures and exceptionally deep snow cover in the days and weeks before the devastating debris flow.