In 1963 a landslide from Monte Toc into the reservoir of the Europe’s highest dam causes a giant flood wave that destroys the village of Longarone and other villages, claiming over 2,000 lives. Europe’s tallest dam is the jewel in the crown of an ambitious Italian hydro-electric scheme. That is, until a landslide occurs, killing more than 2,000 people and baffling scientists.
The Vajont Dam (or Vaiont Dam) is a disused dam, completed in 1959 in the valley of the Vajont River (it) under Monte Toc, 100 km north of Venice, Italy. A 1963 landslide caused the overtopping of the dam and around 2,000 deaths.
One of the tallest dams in the world, it is 262 m (860 ft) high, 27 m (89 ft) thick at the base and 3.4 m (11 ft) at the top. Its 1963 overtopping was caused when the designers ignored the geological instability of Monte Toc on the southern side of the basin. Warning signs and negative appraisals during the early stages of filling were disregarded, and the attempt to safely control the landslide into the lake created a 200 metre tall wave (ten times higher than predicted) that brought massive flooding and destruction to the Piave valley below, wiping out several villages completely.
On 12 February 2008, while launching the International Year of Planet Earth, UNESCO cited the Vajont Dam tragedy as one of five “cautionary tales”, caused by “the failure of engineers and geologists”.
On 9 October 1963, engineers observed trees falling and rocks rolling down into the lake where the predicted landslide would take place. Prior to this, the alarming rate of movement of the landslide had not slowed as a result of lowering the water, although the water had been lowered to what SADE believed was a safe level to contain the displacement wave, should a catastrophic landslide occur. With a major landslide now imminent, engineers gathered on top of the dam that evening to witness the tsunami.
At 10:39 pm, a massive landslide of about 260 million m3 of forest, earth, and rock, which fell into the reservoir at up to 110 km per hour (68 mph) completely filled up the narrow reservoir in front of the dam. The landslide was much faster than predicted, taking just 45 seconds, and the resulting displacement of water caused 50 million m3 of water to overtop the dam in a 250-metre-high (820 ft) wave.
The flooding from the huge wave in the Piave valley destroyed the villages of Longarone, Pirago, Rivalta, Villanova and Faè, killing around 2,000 people and turning the land below the dam into a flat plain of mud with an impact crater 60 metres deep and 80 wide. Many small villages near the landslide along the lakefront also suffered damage from a giant displacement wave. Villages in the territory of Erto e Casso and the village of Codissago (it), near Castellavazzo, were largely wrecked.
Estimates of the dead range from 1,900 to 2,500 people, and about 350 families lost all members. Most of the survivors had lost relatives and friends along with their homes and belongings. The dam itself was largely undamaged — the top metre or so of masonry was washed away, but the basic structure remained intact and still exists today.
Immediately after the disaster, the government (which at the time owned the dam), politicians and public authorities insisted on attributing the tragedy to an unexpected and unavoidable natural event.
The debate in the newspapers was heavily influenced by politics. The paper l’Unità, the mouthpiece of the Partito Comunista Italiano (PCI), was the first to denounce the actions of the management and government, as it had previously carried a number of articles by Tina Merlin (it) addressing the behaviour of the SADE management in the Vajont project and elsewhere. Indro Montanelli, then the most influential Italian journalist and a vocal anti-communist, attacked l’Unitàand denied any human responsibility; l’Unità and the PCI were dubbed “jackals, speculating on pain and on the dead” in many articles by the Domenica del Corriere and a national campaign poster paid for by Democrazia Cristiana (DC). The catastrophe was attributed only to natural causes and God’s will.
The campaign accused the PCI of sending agitprops into the refugee communities, as relief personnel; most of them were partisans from Emilia Romagna who fought on Mount Toc in the Second World War and often had friends in the stricken area.
Democrazia Cristiana, the party of prime minister Giovanni Leone, accused the Communist Party of ‘political profiteering’ from the tragedy. Leone promised to bring justice to the people killed in the disaster. A few months after he lost the premiership, he became the head of SADE’s team of lawyers, who significantly reduced the amount of compensation for the survivors and ruled out payment for at least 600 victims.
The DC’s newspaper, La Discussione, called the disaster “a mysterious act of God’s love”, in an article that drew sharp criticism from l’Unità.
Apart from journalistic attacks and the attempted cover-up from news sources aligned with the government, there had been proven flaws in the geological assessments, and disregard of warnings about the likelihood of a disaster by SADE, ENEL and the government.
The trial was moved to L’Aquila, near Rome, by the judges who heard the preliminary trial, thus preventing public participation, and resulted in lenient sentencing for a handful of the SADE and ENEL engineers. One SADE engineer (Mario Pancini) committed suicide in 1968. The government never sued SADE for damage compensation.
Subsequent engineering analysis has focused on the cause of the landslide, and there is ongoing debate about the contribution of rainfall, dam level changes and earthquakes as triggers of the landslide, as well as differing views about whether it was an old landslide that slipped further or a completely new one.
There were a number of problems with the choice of site for the dam and reservoir: the canyon was steep sided, the river had undercut its banks, and the limestone and clay-stone rocks that made up the walls of the canyon were inter-bedded with the slippery clay-like Lias and DoggerJurassic-period horizons and the Cretaceous-period Malm horizon, all of which were inclined towards the axis of the canyon. In addition, the limestone layers contained many solution caverns that became only more saturated because of rains in September.
Prior to the landslide that caused the overtopping flood, the creep of the regolith had been 0.4 inches per week. In September, this creep reached 10.0 inches per day until finally, the day before the landslide, the creep was measured at 40.0 inches (1 m). At 10:39pm, on the 9th October, it was the sudden and unexpected high speed of the landslide that proved to be catastrophic, and ultimately caused the flood.