khoji parkDisasters · Vajont Valley · 1963
A Mountainside Fell Into a Reservoir and Overtopped the Dam
A massive landslide in 1963 triggered an overtopping wave below the Vajont Dam.
Read in slides1. Dam Construction
During the late 1950s, the electricity monopoly SADE constructed the Vajont Dam in northern Italy. Designed as one of the tallest dams in the world, the concrete structure spanned a narrow gorge under Monte Toc. Engineers planned to harness regional rivers to generate hydroelectric power for industrial expansion. Geological surveys failed to adequately assess the structural stability of the surrounding mountain slopes.
Construction work concluded at the end of the decade.
2. Early Warnings
Shortly after filling operations began, workers noticed ground fractures and small landslides along Monte Toc. Independent geologists warned managers that the entire side of the mountain was unstable and prone to collapse. Government authorities and company officials dismissed these warnings and prosecuted journalists who reported the hazards. Filling continued despite mounting evidence of geological risk.
Officials ignored warnings regarding mountain stability.
3. Reservoir Testing
Following a major landslide in 1960, SADE lowered the water level and constructed an artificial bypass gallery. Hydraulic model experiments conducted in 1962 indicated that future landslides could generate dangerous displacement waves. Engineers calculated safe reservoir limits to prevent water from overtopping the dam crest. Responsibility for the facility transferred to the national energy agency ENEL in 1963.
Engineers conducted hydraulic model experiments.
4. Imminent Collapse
Throughout the summer of 1963, alarmed local residents repeatedly reported ground tremors and rock movements. On September 15, a massive section of the mountain slid downward by nearly a meter. ENEL managers decided to slowly empty the basin to mitigate potential risks. By early October, the collapse of the southern flank appeared completely unavoidable.
Mountain creep accelerated during early October.
5. The Landslide
On the night of October 9, 1963, a colossal mass of rock and earth broke off Monte Toc. Approximately 260 million cubic meters of material plunged into the reservoir at high speed. The impact generated a violent seismic shock and displaced millions of water liters. Within seconds, the landslide completely filled the basin behind the dam structure.
Millions of cubic meters collapsed into the reservoir.
6. Overtopping Wave
The displacement wave surged over the crest of the dam in a massive sheet of water. A large portion of the water roared down into the narrow valley below. Additional waves destroyed several villages situated along the lake shores. The concrete dam wall remained structurally intact, retaining two-thirds of the reservoir water.
Floodwaters overtopped the concrete dam wall.
7. Valley Destruction
The overtopping flood swept into the Piave Valley and obliterated the town of Longarone. Debris and mud flattened buildings and left an impact crater in the landscape. Approximately two thousand people lost their lives in the disaster. Survivors faced widespread destruction and the loss of entire families.
Flooding destroyed several villages and killed thousands.
8. Rescue Operations
Firefighters and military units arrived to search for survivors and recover victims from the mud. Soldiers dug by hand through thick debris to locate missing residents. Rescue teams faced severe access challenges due to destroyed roads and bridges. Medical personnel established emergency stations to treat injured survivors.
Military units deployed to assist recovery efforts.
9. Political Debates
In the aftermath, conservative newspapers and political figures initially attributed the catastrophe to unavoidable natural causes. Opposition media and communist publications denounced management negligence and government cover-ups. Subsequent legal trials resulted in lenient sentences for a handful of engineers. Later civil judgments mandated compensation payments to affected municipalities.
Public authorities initially blamed natural factors.
10. Memorial Legacy
The landslide displaced reservoir water over the dam and into the valley, devastating Longarone and nearby communities in October 1963. The concrete dam largely remained standing. Investigations and prosecutions therefore concerned the slope, reservoir management and warnings as well as the structure. A surviving dam did not mean the populated valley below had escaped the water forced out by the slide.
The dam stood while the displaced water devastated the valley.