Early Signs of Disaster
Throughout the summer of 1960, minor landslides and earth movements were noticed; however instead of heeding these warning signs, the Italian government chose to sue the handful of journalists reporting the problems for "undermining the social order."
On 4 November 1960, with the water level of the basin at about 190 metres of the planned 262, a landslide of about 800,000 m³ collapsed into the lake. SADE stopped the filling, lowered the level by about 50 m and started to build an artificial gallery in the basin in front of Monte Toc, to keep the basin usable even when the expected further landslides divided it into two parts.
In October 1961, after the completion of the gallery, SADE restarted the filling of the narrow basin under controlled monitoring. In April and May 1962, with the basin water level at 215 metres, the people of Erto e Casso reported five earthquakes of 'grade five' on the Mercalli scale, though SADE downplayed their importance. SADE was then authorized to complete the filling up to the maximum level.
In July 1962, SADE's own engineers reported the results of model-based experiments on the effects of further landslides from Monte Toc into the lake. The tests indicated that a wave generated by a landslide could top the crest of the dam if the water level was 20m or less from the dam crest. It was decided that a level 25m from the crest would be safe level. However, a decision was made to fill the basin beyond that, because the engineers thought they could control the rate of the landslide by controlling the level of water in the dam.
In March 1963, the dam was transferred to the newly constituted public company for electricity, ENEL. In the following summer, with the basin almost completely filled, slides, shakes and movements of the ground were continuously reported by the alarmed population. On 15 September the entire side of the mountain moved down by 22 cm. On 26 September, ENEL decided to slowly empty the basin down to 240 m, but in early October the collapse of the mountain's south side looked unavoidable: one day it moved almost 1 m. There is no known record of any warning or displacement order being issued to the populace.
Read more about this topic: Vajont Dam
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