I reach the parking lot upstream the dam and I am even more confused.Drivers horning, shuttling buses and tourists that, in single line, are preparing to climb to the top of the structure. I never expected so many people on a rainy April day.
I try to join one of these groups, after all today I’m a tourist too. We are close to the right entrance of the crowning, a few meters from a plaque in memory of the disaster. The guide begins his story and I understand from the passion with which he speaks that it is not yet another empty repetition of a text learned by heart.
On the night of 9 October 1963, about 270 million cubic meters of rock broke off from Mount Toc. But the figures, presented in this way, say little or nothing even to the most experienced geotechnician. You have to take them apart, compare them, to understand them. With the same amount of material collapsed in the Vajont basin, approximately two hundred football fields could be filled with a layer of earth almost 200 meters high. And, if this layer was removed from one hundred trucks, it would take seven centuries to completely remove it. To say that the entire side of the mountain collapsed is not an understatement.
If I turn left, I can clearly see the sliding plane of the landslide. Its upper front has an ironic “M” shape, like the initial of the Austrian geologist Müller. His was the first report to describe the existence of a paleo landslide as early as 1961 but, as future events show, it was not heard. The last thing the guide explains to us is the speed with which this mass of earth, rock and water slipped into the basin. According to expert estimates, it reached 90 km/h. Thus, in just 45 seconds it even managed to go up the opposite slope. The water collected by the dam was pushed in two directions, reaching a height of 250 meters: a wave, upstream, lapped the villages of Erto and Casso; another, towards the valley, was so high as to overcome the enormous hydraulic structure like a tsunami and hit Longarone, accelerated by the narrow gorge.