Stava's tailings dams collapsed in 1985 — 268 people died from poor maintenance

Prealpi Mineraria operated a fluorite processing plant in the Stava valley in Trentino, northern Italy. The plant's tailings — the muddy slurry left after fluorite was extracted — were stored behind two earthen dams built one above the other in the Rio di Stava valley. The upper dam had been raised repeatedly over the years as more waste accumulated, and a drainage pipe running through it was meant to keep water pressure under control.

On the morning of 19 July 1985, the upper dam collapsed without warning. The drainage pipe had sagged under the weight of sediment, reducing its capacity. Water continued to be pumped into the reservoir, but it could not drain fast enough. Pressure built inside the dam bank until water found a path through it, causing soil liquefaction. The bank failed, releasing approximately 180,000 cubic metres of mud, sand and water. Thirty seconds later, the torrent crashed into the lower dam and destroyed it too. The liquefied mass travelled down the valley at 90 km/h.

Within minutes it had crashed through the village of Stava, destroyed 63 buildings and 8 bridges, and killed 268 people — 247 of them in the village itself. The mudflow continued for 4.2 km until it reached the Avisio River. The disaster remains one of Italy's deadliest industrial accidents and one of the worst tailings-dam failures in history.