Sunday, February 28, 2016

Vajont Dam Landslide Remote Tour Including Street View of Geologic Investigation

The 1963 landslide at Vajont in northern Italy was an horrific event that killed 2,500 people. The slide involved the a very large collapse of a bedrock mountainside into a new reservoir that was filling behind a dam constructed in a narrow canyon. The slide displaced a huge part of the lake over the dam with many of the fatalities downstream of the dam as well as hundreds of meters up the slope across from the slide. The slide speed has been estimated at over 60 miles per hour based on the wave of water generated as the slide displaced the lake.

Dave Petley has put up several posts on the slide and provides an excellent description of the slide and the events leading up to the slide including engineering efforts to monitor and control the slope failure before the rapid collapse of the slope: the-vajont-landslide-of-1963. The post also includes a list of references of papers published on the slide

As a fair bit of my work is assessing geologic hazards I took a remote tour of the slide via Google earth. The tour included a surprise street view scene of active geologic investigation of the landslide.

Outline of landslide area (south is towards the top)

Note Casso at the bottom of the image. I am not sure if the town is in the same spot as in 1963, but the 1963 town was destroyed by the wave of water that surged up the slope. Towns in the valley to the west (north is towards the bottom of the image) were all destroyed.

Street view of top of dam with slide in the background
Note the bedding surface orientation of limestone units

The dam survived the slide. Hydro power is now generated via a tunnel to the lake that has formed behind the landslide.

View of slide from near Casso 
The road in the image is traversing up the toe of the landslide

View of slide from the upper toe of the slide from the road shown in the image above

Road on the landslide with GPS surveyor

Seismic line stations along road 

The seismic survey consists of a string of recorders that will pick up shock waves traveling through the subsurface. The waves travel at different speeds through different materials, are reflected or refracted off of sharp contrasts. Hence, the recordings can be used to map the subsurface.

Andrea Wolter summarizes a recent paper on Vajont on the Landslide Blog: the-vajont-slide.

The Vajont slide took place during the era of large dam building throughout the world. As such, the failure has generated much interest in engineering geologists and geotechnical engineers. The topic of new large dam projects is raised more frequently as a means to address climate change impacts. Vajont is a lesson that needs to be well understood before projects are undertaken - a lot can go wrong.

1 comment:

Sam Crawford said...

Wow, what a disaster.

"The Vajont Dam as seen from the village Longarone in 2005, showing approximately the top 60–70 metres of concrete. The wall of water that overtopped the dam by 250 metres (820 ft) and destroyed the villages would have obscured virtually all of the sky in this photo."