The Vajont Dam Disaster
The Vajont Dam Disaster
Now… I know what you’re thinking. This is a dam. Where’s the water?
That is where this gets interesting.
The Vajont Dam lies on Vajont River in Italy. It was built in the late 1950s and was 262 meters tall, making it one of the tallest dams in the world at the time and even today.
The area it was built on, the Vajont River gorge, was known to be geologically unstable even before the construction of the dam; however, Italy’s growing demand for electricity spurred construction anyway.
The dam’s construction began in 1956 and finished around 1960. It was done by a company called Società Adriatica di Elettricità (SADE), one which essentially had a monopoly on the Italian energy industry.
As construction began, people already began noticing some irregularities in the mountains surrounding the dam. When building a road onto the side of the mountain to the dam (pictured above), people began noticing tears and fissures in the ground.
Many were especially concerned that filling the reservoir would undermine the integrity of the mountains around it, and many experts warned of the risks of filling the reservoir too quickly and the possibility for a single disastrous landslide. Yet, SADE mostly ignored the warnings and, according to some sources, the Italian government suedjournalists who covered the issue for “undermining social order.” Despite these concerns, which were considered to be worst-case scenarios, SADE completed the dam and began filling the reservoir in 1960.
When the lake reached 180m deep (of the planned 260 m), a landslide of nearly 1,000,000 cubic meters collapsed into the lake. It was a warning sign. Technicians quickly lowered the lake level.
In the diagram below, the first failure is circled in blue.
At this point, engineers realized that the water-logged left side of the mountain was inherently unstable. However, controlling the whole mountainside would be an impossible feat. One of the lead engineers even said, “It appeared hopeless to arrest the slide artificially, because all means that would have had to be applied were beyond human bounds.” Thus, dam technicians decided to carefully monitor the neighboring mountains and control the water level.
After about a year and a half of careful control, SADE workers began raising the dam’s water level — fast. In the period of about 3 months, the water level was raised from 185m to 231m. By September of 1962, the level was at about 235 m. At that point, experts monitoring the mountain reported the land moving at up to 3.5 cm/day, up from levels at 0.3 cm/day just a year earlier.
At around this time (July 1962), SADE engineers did an analysis of the mountainsides around the dam and determined that, in the event of a landslide, if the land was moving at 20 MPH and the water was 20m below its maximum level, the wave would not top the dam. Thus, the water was kept at 25m below its maximum level, at 235m.
Enter October 9, 1963.
Engineers began seeing trees and rocks falling in the area where the landslide was predicted to occur.
They relax for a moment. If everything goes to plan, nothing major will happen. A small wave will form, hit the dam, and everything will go back to normal.
At 10:39 PM, a massive landslide of 260,000,000 cubic meters of earth, forest, and rock begins to hurtle downward at an incredible 68 MPH, more than 3 times the original predicted speed.
A huge 250m wave formed, topping the dam and rushing toward the valley below. Within moments, the villages of Pirago, Villanova, Rivalta and Fae were totally decimated. Thousands of lives were lost.
This was the dam before and after the collapse:
In the towns, there was nothing but total destruction:
I think this incident serves as a reminder that we can not put total faith in the idea of technological progress. Caution is always needed, especially in troubling circumstances like this one. If the warnings were adequately heeded, this disaster could have been averted.
Either way, it is definitely one of the greatest man-made disasters of all time.
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