Malpasset Dam
The 928th tallest dam in the world
The Malpasset Dam was an arch dam (convex surface facing upstream) on the Reyran River, north of Fréjus on the French Riviera. It collapsed on 2 December 1959, killing 423 people in the resulting flood. The breach was caused by a tectonic fault in the impermeable rock base, which had been inadequately surveyed. Nearby road-building works, using explosives, may also have contributed to the disaster.
Dam data from Wikidata (CC0) plus curated additions. Summary from Wikipedia (CC BY-SA).