http://www.sci.port.ac.uk/geology/staff/dpetley/imgs/enggeolprac/vaiont1.html
Vaiont Dam, 262m high, on the Vaiont River, a tributary of the Piave River, in Venetia, NE Italy in the south-eastern part of the Dolomite Region of the Italian Alps, near Belluno, about 100 km north of Venice. The dam, one of the highest in the world, was completed in 1961 and is used to generate HEP for the rapidly expanding northern cities of Milan, Turin and Modena. After heavy rains in 1963, landslides into the Vaiont reservoir caused the stored water to spill over the dam, sweeping away the village of Longarone and flooding nearby hamlets. The Vaiont reservoir disaster is a classic example of the consequences of the failure of engineers and geologists to understand the nature of the problem that they were trying to deal with. During the filling of the reservoir a block of approximately 270 million m3 detached from one wall and slid into the lake at velocities of up to 30 m sec-1 (approx. 110 km h-1). As a result a wave over topped the dam by 250 m and swept onto the valley below, with the loss of about 2500 lives. Remarkably the dam remained unbroken.
http://www.sci.port.ac.uk/geology/staff/dpetley/imgs/enggeolprac/vaiont1.html