The Vajont Dam disaster is a sad reminder of what can happen when early warnings about a specific construction aren't taken into consideration.
Though the Vajont Dam actually stayed intact during the disaster, it stands as a testament to how important it is for engineers and geologists to understand the natural environment surrounding a complex structure.
Here are 13 facts to help you understand how the disaster happened, as well as what happened in its aftermath and how it affected local communities.
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1. The dam was built during Italy's postwar boom
The construction of the Vajont Dam was undertaken during the postwar boom in Italy, which is also known as the Italian economic miracle by historians. It was a period in which Italy saw surprisingly strong economic growth after the Second World War and up until the late 60s.
During this time, several ambitious engineering projects — including Genoa's Morandi Bridge — were set in motion. Unfortunately, in the case of the Vajont Dam, ambition seems to have clouded the judgment of those planning the project.
2. Warnings about the construction were ignored
Vajont Dam was built to create a reservoir from a mountain stream in order to generate hydroelectric power. Before construction, engineers and geologists were warned by locals that the land surrounding the foot of mountain Monte Toc, the planned site for the dam, was unstable.
During construction, tremors and landslides were reported. However, the operators – Italian electricity corporation Sade, and the newly created national power company Enel – largely turned a blind eye to the warning signs.
During construction, worries that the work had triggered worrying seismic movements seem to have been largely ignored. Despite the warnings, construction continued apace to build the tallest hydroelectric dam of the time. Construction was completed in 1959.
3. The disaster started with a landslide
Towards the end of construction, a landslide behind the dam began to seem inevitable. However, the impact and size of the landslide were vastly underestimated.
The operators decided to lower the water level in the reservoir as a safety measure — experts have since said the lowering of the water level at the foot of Monte Toc, combined with heavy rain, may have actually helped to trigger the disaster.
Late in the evening of October 9, 1963, a large chunk of Monte Toc, 400m (1,312ft) deep and roughly the size of a small town broke away and slid down the mountainside. The animation above gives an idea of the scale of the incident.
In just 45 seconds, the landslide reached the reservoir and displaced 50,000,000 cubic meters of water, creating a 250-meter high wave to go flying into the sky.
4. The ensuing wave destroyed entire villages
The enormous wave caused flash flooding in the Piave valley, below the dam, and destroyed the villages of Longarone, Pirago, Rivalta, Villanova and Faè.
As the before and after images above attest, the area near the dam was flattened and turned into a flat plain of mud.
The worst affected village was Longarone, which was directly below the dam.
5. The death toll was approximately 2,000
80% of the inhabitants of Longarone and surrounding villages did not survive the huge deadly wave that was caused by the landslide behind Vajont Dam.
Due to the large expanse of the area affected, the exact death toll is sadly not known, though estimates range from 1,950 to 2,000. Entire buildings, communities, and families were wiped out.
Only 30 of Longarone's children survived the disaster.
6. The wave created an air pocket with the power of an atomic bomb
The crashing wall of water created an air pocket when it hit the ground, which was more powerful than the Hiroshima bomb. It was so strong that victims are reported to have been found naked, their clothes blown off by the exploding air.
A survivor Micaela Colletti, who was 12 at the time, told the BBC, "I felt my bed collapsing as if there was a hole opening up beneath me and an irresistible force dragging me out. I couldn't do anything. I had no idea what was happening."
7. Survivors said they heard a sound like a thunderclap
Survivor Micaela Colletti described the evening of the event to the BBC. "I heard what I thought was a thunderclap," she explained.
"It was incredibly loud. My granny came into my room and said she was going to close all the shutters because a storm was coming.
"At exactly the same moment all the lights went out and I heard a sound, impossible to describe properly. The closest thing I've ever heard to it is the sound of metal shop shutters rolling down, crashing shut, but this was a million, a billion times worse."
8. After many years, the incident was recognized as an engineering disaster
The Vajont Dam was a government initiative, and as is often the case with such big disasters, the authorities avoided taking responsibility for the landslide for years after it occurred.
As The Local explains, following the disaster, the Italian government insisted that the landslide was an unforeseeable "act of god." The disaster became highly politicized, with the opposition in Italy's parliament calling out the government's negligence, while the ruling party tried to rewrite the history of the events leading up to the disaster.
In 2008, however, UNESCO publicly called the incident "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."
9. UNESCO calls it one of the worst man-made environmental disasters of all time
The disaster was, according to the UN Scientific and Cultural agency UNESCO, one of the worst man-made environmental disasters of all time, and is definitely the worst in Italy's history.
The wave caused by the landslide wiped out 350 families altogether and shocked the entire nation.
News footage of the time still exists, showing grainy black and white images of a landscape that was once the village of Longarone, but looked more like a barren moon landscape following the incident.
10. A new town was built to resettle the survivors
While Longarone and other villages in the Piave valley were rebuilt, most of the survivors of the Vajont Dam disaster were moved into a newly built village dubbed Vajont.
At the site of the disaster, a new pump system was added to the Vajont Dam's basin to help keep the lake at a constant level.
The dam's bypass gallery, meanwhile, was lengthened so as to let water flow safely down to the Piave valley.
11. A memorial church now stands as a stark reminder of the disaster
Today, the village of Longarone is home to a memorial church that was designed by the Italian architect Giovanni Michelucci.
The church stands near the Vajont Dam. Its interior slightly resembles the dam itself, with its strikingly slanted concrete walls.
Though it was built as a place for visitors to pay their respects, the surviving parish priest from Longarone is reported to have been strongly opposed to the construction of the Vajont Dam memorial church.
The village of Erto, which was on the shore of the reservoir, also built a visitor center with information about the disaster.
12. Some survivors aren't happy with recent changes to the memorial
Changes that were recently made to the cemetery for victims of the disaster have unfortunately served to resurface the trauma for some surviving relatives. A few years ago, the local authorities decided to renovate the cemetery. In doing so, they removed a wealth of personal memorials and mementos added by relatives.
As Ms. Colletti told the BBC, gravestones were also added for all of the missing unknown dead from the disaster. While this served to pay tribute to those that were never found, it also caused confusion.
Ms. Colletti used to know where her father's remains lay, now his gravestone has been moved to stand alongside her entire immediate family, the rest of whom were never found but were presumed dead.
"It is," she said, "like losing your father all over again. This is a false history. It doesn't tell the true story because it doesn't show how few of the dead were ever identified. Before, it did. Now - no."
13. The Vajont Dam survived the disaster and still stands today
Impressively, Vajont Dam was relatively unscathed by the landslide and the ensuing wave. The structure, which only suffered minor superficial damage, still stands today and was partially opened to the public in 2002.
Guided tours allow people to walk along the top of the dam as well as nearby locations while learning about the history of the disaster.
Today, Vajont Dam reminds us of the immense human cost that can come from ignoring warning signs in large civil engineering projects. A sad cautionary tale of the folly of organizations and companies that put their ambitions above the safety of others.