On 19th July 1985, a mineral waste facility made up of two tailings dams collapsed in the Stava valley (Municipality of Tesero, Province of Trento, Italian Alps). This facility served a fluorite mine and was raised over a period of more than 20 years in order to decant, consolidate and store the tailings resulting from the froth flotation process of the Prestavèl mine and other fluorite mines of Trentino, South Tyrol and Lombardy.
Origin
The Prestavèl Mine The Prestavèl mine is located on the western and southern slopes of Mt. Prestavèl at an altitude of 1500 to 1900 m a.s.l. The mine deposits had been exploited safely since the
The failure
At 12h 22′ 55″ on 19th July 1985 the dam of the upper basin failed and collapsed onto the lower basin, which also failed.The mudflow composed of sand, slime and water moved downhill at a
Causes
The reason for the collapse The collapse was caused by the chronic instability of the dams, especially the upper one, which were below the minimum factor of safety required to avoid failure. In particular, the
Legal liability
The first trial took place in Trento and was concluded in less than three years. Legal proceedings ended after another four levels of judgment with the second sentence pronounced by the Supreme Court, which was