Newly Built Dam Collapsed, Killing Hundreds

The collapse of the Malpasset Dam in France in 1959 was deeply ironic: the dam gave way despite having only recently been built.

According to a report by France’s Ministry for Ecological Transition, the disaster occurred on 2 December 1959.

The dam had just been completed when the region was hit by several consecutive days of heavy rain. It burst at 9.11pm during its first filling, releasing a torrent of 50 million cubic metres of water that swept through the Reyran Valley and destroyed everything in its path.

The town of Fréjus was flooded within minutes and was struck by a wave of mud 21 minutes later. It was completely cut off for several days after transport links, telephone lines, electricity and water supplies were severed.

Hundreds of metres of the RN 7 national road and railway line were swept away, while a layer of mud up to 50 centimetres thick covered several areas.

The disaster killed 421 people. A further 7,000 were left homeless and forced to evacuate.

The cause of the dam’s collapse

The collapse was caused by uplift forces associated with a geological fault, combined with rock-mechanics behaviour that was not understood at the time of construction.

The quality of the dam’s arch structure and concrete was considered very good. The disaster was therefore attributed entirely to a defect in the underlying rock foundation on which the dam stood. No court assigned fault or legal liability to the dam’s builders.