Seconds From Disaster - Flood at Stava Dam

The Val di Stava Dam collapse occurred on 19 July 1985, when two tailings dams above the village of Stava, near Tesero, Northern Italy, failed. It resulted in one of Italy's worst disasters, killing 268 people, destroying 63 buildings and demolishing eight bridges.

The upper dam broke first, leading to the collapse of the lower dam. Around 180,000 cubic metres of mud, sand, and water were released into the Rio di Stava valley and toward the village of Stava at a speed of 90 km/h. Having crashed through the village, the torrent continued until it reached the Avisio River a further 4.2 km away, destroying everything in its path.
An investigation into the disaster found that the dams were poorly maintained and the margin of safe operation was very small.[1]

A pipe in the upper dam used to drain water had begun to sag under the weight of sediment, making the dam's drainage less effective. Meanwhile, water continued to be pumped into the reservoir behind the dam, which, coupled with the less efficient drainage, meant the pressure on the bank of the upper dam began to increase. Following the path of least resistance, water began penetrating the bank, causing the soil within to liquefy and weaken the bank until it failed. The water and tailings from the upper dam then flowed into the lower dam, which, under the immense pressure produced, failed thirty seconds later.