Vaiont Dam, Italy

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Vaiont, Italy, 1963
The nearly 300-meter tall Vaiont Dam was the tallest in Europe when it was completed. In the fall of 1963 heavy rains weakened a shale layer south of the reservoir. On October 9 the shale gave way and the overlying layers slid downhill into the reservoir. The dam, amazingly, was nearly undamaged. Instead, water from the reservoir was simply pushed up the opposite valley wall and around the dam. The first casualties were some dam workers staying in a hotel 100 meters above the dam. The water then poured down-valley, wiping out much of the village of Longarone and several smaller villages. 1800 people died.

Approach From The South

I was expecting this to be technically and geologically interesting, historic, tragic, and poignant. I was not expecting the scenery to be breathtakingly beautiful as well. At left and below are scenes on the way north to Longarone.

Longarone

Below: approaching Longarone. The dam is located in the deep cleft (hidden behind the smokestack in the left view). The large bare rock exposure is not the 1963 landslide, which is on the opposite side of the valley.
The mouth of the gorge where the Vaiont Dam is located.
Sign for Longarone, the town hardest hit by the 1963 disaster. The gorge leading to the dam is behind the sign.
Looking south from Longarone. The steep wooded peak is reminiscent of Machu Picchu.

Below: even from the mouth of the gorge, only a bit of the dam is visible.

Left: this bridge provides access to the road leading to the dam. Longarone is in the distance.

 

Left and below: mountain views near the confluence of the gorge and the river.
Left: some of this gravel plain may be debris from the 1963 flood, but more likely it's material carried by the river during normal flood stages.
Left: the very mouth of the gorge. The waterfall flows over a low concrete dam. The main dam is mostly hidden around the distant bend. The arches appear to be remnants of old bridges.
Left: looking down into the slot gorge.
Left: the waterfall with the main dam peeping around the corner of the gorge.

The Dam and Slide Area

Much of the region is a park. That's one of the longer URL's around!
Left: a small hut a few hundred meters east of the dam has an information center. The main visitor center is in Erto a few kilometers to the east.
Left: map at the information hut.
Left: geologic column of the gorge. The yellow material was the landslide. Shaly beds at the Jurassic-Cretaceous contact (Giurassico-Cretacico) were the lubricating layer that allowed the slide to move.

The Scaglia Rossa (Red Scaly Rock) is famous because it was during study of this unit that Walter Alvarez stumbled onto evidence that a meteor impact had caused the extinction of the dinosaurs.

Below: views of the landslide scar. My first impression, on seeing how smooth and steep the slide surface was, was "What the @#$& were they thinking?" Textbook maps don't prepare you adequately for how rugged the topography is nor how steeply dipping the strata are.
Left and below: looking east across the slide area. The jumble of large blocks is very reminiscent of the Mount Saint Helens slide.
Left and below: views of the upstream face of the dam. There are about 200 meters of landslide debris filling the gorge behind the dam. The spire right of the dam is the memorial chapel.

Note that the rocks immediately left of the dam are dipping away from the dam. The small saddle on the hill above is the axis of a syncline.

Left: upstream side of the dam.
Left: From a structural standpoint, the dam was magnificent, a thin arch dam in which the mass of the water compressed the upstream side and made it stronger. From a site selection standpoint, it was another matter.

Memorials

Left: the memorial chapel.

Below: victims commemorated on blocks outside the chapel.

Left: tablet inside the chapel commemorating victims.

Downstream

Left: outcrops above and north of the dam.
Left and below: looking into the gorge below (west of) the dam.
Left: former dam spillway.
Left: damaged south end of the dam, with the landslide scar beyond.
Left and below: views of the downstream face of the dam.
Left: footbridge below the dam. The spillway on the nearer cliff carries water from the remnant of the reservoir to the east.

The Road

Above: the cliffs along the road are a cobweb of chain link, cables and rock bolts.Below: views of the road tunnels leading to the dam.
Left: inside the tunnel.
Left: in one of the side galleries of the tunnel are private memorials.
Left: east end of the tunnel, looking at the memorial chapel.
Left: the south end of the dam was the only section that suffered significant damage, and even here only about a meter or two of the lip was eroded away.

East of the Dam

Left: former road between intact bedrock (left) and landslide debris (right).
Looking east where the present road cuts through the slide debris.
Left and below: remnants of the reservoir at the east end of the slide. A drainage tunnel keeps the water level from overtopping the slide and draining the lake catastrophically. A similar tunnel keeps Spirit Lake, at the foot of Mount Saint Helens, from doing the same thing.
 
Looking southeast. The east end of the slide is the bare bank in the foreground.

Below: looking northwest past a large landslide block toward the village of Casso. Casso was unharmed by the flood by virtue of its high elevation.

Casso

Left: looking west down the gorge from the road to Casso.

Below: the short but extremely winding drive up to Casso provides wonderful comprehensive views of the landslide scar and the slide itself.

Above and left: barely visible slightly below and right of center in both pictures is a small pond on the upper edge of the landslide. The pond was impounded by back rotation and lateral spreading of the slide block

Below: views of the distal edge of the slide show that a slab hundreds of meters long maintained its coherence during transport.

Left: view of the large slab, heavily fractured internally but basically transported as a unit.
Left: view southeast over the landslide scar.
Left: roadside shrine near Casso.

Below: Casso is so darn cute you just about want to give it a hug and take it home with you.

 

North of Longarone

Left: looking south from Longarone.

Below: views north of Longarone.


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Created 22 June 2007, Last Update 01 July 2012

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