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Update #2 ·

French Malpasset Dam after the disaster

Malpasset Dam was a built on similar kind of geological ground than adonis valley with lot of field infiltrations.

The result is impressive... It collapsed on December 2, 1959, killing 423 people in the resulting flood, 2 billion of francs of damages.

The breach created a massive dam break wave, or wall of water, 40 metres (130 ft) high and moving at 70 kilometres (43 mi) per hour, destroying two small villages, Malpasset and Bozon, the highway construction site, and in 20 minutes, still standing 3 metres (10 ft) high, reaching Fréjus.

Various small roads and railroad tracks were also destroyed, water flooding the western half of Fréjus and finally reaching the sea.

Geological and hydrological studies were conducted in 1946 and the
dam location was considered suitable.

Due to lack of proper funding, however, the geological study of the region was not thorough.

The lithology underlying the dam is a metamorphic rock called gneiss. This rock type is known to be relatively impermeable, meaning that there is no significant groundwater flow within the rock unit, and it does not allow water to penetrate the ground.

But they didnt took into consideration also the topography and the field infiltrations which were important factors of the collapse.

Weeks before the breach, some cracking noises were heard, but they were not examined. It is not clear when the cracking noises started.

A tectonic fault was later found as the most likely cause of the disaster. The water was collected under a wall and unable to escape through the rocks then the dam has collapsed.

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