The Stava mudflow of 19 July 1985 (Northern Italy): a disaster that effective regulation might have prevented

Abstract. The disaster occurring in the Eastern Italian Alps in the summer of 1985 was caused by the failure of two tailings dams located just upstream from the village of Stava in the municipality of Tesero (Trento province, Italy). The structure comprised two small storage basins for the deposition of tailings from the separation process of the Prestavel fluorite mine. On their downstream sides, the basins were contained by steep earth embankments, whereas upstream they rested directly on the natural slope. The total height from the base of the lower dam to the crest of the upper dam was over 50 m. On 19 July 1985, the front of the upper dam suddenly burst, triggering a vast mudflow (180 000 m3) that flowed down-channel through Stava, a small village of 20 buildings. The mudflow rapidly traveled over 4.2 km along the Stava Valley and passed through Tesero, before flowing into the Avisio River. The mudflow destroyed many buildings and resulted in 268 fatalities and 20 injuries. From an analysis of the data collected and field observation, several factors may be cited as having contributed to increasing instability, as the upper dam continued to be raised until the disastrous collapse of 19 July. Foremost among these factors is the mistaken assumption that the tailings deposited in the impoundments would consolidate fairly quickly. Indeed, no monitoring system was ever installed to verify the assumed consolidation. Other operational shortcomings and construction errors were contributing factors. Regulations requiring construction standards, operational monitoring, and independent periodic inspection could have prevented this disaster. Comprehensive legislation is required to effectively limit the adverse consequences of tailings dam failures by providing a regulatory environment where the safety and welfare of the local area can be balanced with the economic benefits of mining operations