1. MARIA CHINI VIKI IOANNOU THEMISTOKLIS TERATSIAS

2. o Vajont valley: part of the NE Italian Alps region o The dam is located between the mountains Toc and Salta o Narrow, deep side slopes and glacial morphology o Height: 262 m above the valley floor o Width: 190 m at the top and 27 m at the bottom o Construction: 1956-1960 o Volume: 150 million m³ of water

3. o Vajont Valley dominating rocks : Limestones Dolomites o Two locations under consideration o Location with more rigid limestones and bigger dam capacity More or less fractured

4. Colle Isolato (1959): Provides evidence for the existence of the prehistoric landslide o Overlying alluvial deposits from old river o Different from in-situ rock mass

5. o June 1960: a report pointed out that potential reservoir filling would cause sliding o July 1960: a report indicated that sliding could occur only in the surface o December 1959: seismic velocity of rock 5,000-6,000 m/s o Reduced to 1,000-2,000 m/s in one year

6. o 4 th November 1960: a mass of debris estimated to 700,000 m 3 slipped o May 1960 - August 1963: seismographs placed on the dam o May 1963: Velocity of slip 1 mm/day o August 1963: Velocity of slip 5 mm/day

7. o By September the velocity of movements = 20mm/day => Operations to lower reservoir level began => Velocity continued to increase rapidly 9 th of October 1963, at 22.39: Sudden slide of the main rock mass

8. o Landslide detached from the southern slope of Mt. Toc o Volume of the landslide = 270 million m 3 o Collapsed in 45s o 25 million m 3 of water was displaced o Wave crested 140 m above the dam’s crest and that still had a height of 70 m downstream

9. o Energy of spilled water = 1.5 x Hiroshima’s atomic bomb o The wave hit the town of Longarone and other villages killing more than 2000 people o The dam remained almost intact even if the load at the abutment was 8 times greater than design load

10. Generally agreed that failure happened along bands of clay (5-15 cm thick) inside the limestone mass: Clay layers

11. Landslide initiation factors: I.Prehistoric landslide located in the northern part of the slope : => Reactivated by the water level rise II.Clay layers below slide => Mobilized by the increase of water pore pressures High velocity of displacement: I.Existence of the old landslide indicates a low friction angle of rock mass => low resistance in movement II.Frictional heat created a cushion during sliding and converted slow rate sliding into rapid failure

12. I. Presence of cataclastites in mylonitic zone: fault plane II. Seismic activity: no connection with the formation of Vajont gorge III. Wrong interpretation: increasing water level not favourable IV. Omission: to analyse the slope or take a sample for laboratory tests V.The superficial slides: verified but they were deeper than expected VI. Rock degradation: indication that the rock was not as strong as before

13. Carlo Semenza was aware of the problems: “...things are probably bigger than us and there are no adequate practical measures...” “...I am in front of a thing which due to its dimensions seems to escape from our hands...”

14. o Modification in the design standards of ongoing projects o Geodetic station => sustain water level in safe limits o Microseismic monitoring => localize and forewarn for an oncoming slope failure o Acoustic emissions => forecast future movements o Engineers and geologists observe and inspect the slopes of projected basins

15. o Construction giant dams need to take all factors under consideration o Continue checking, supervising and maintaining the construction, after its completion There are always unpredictable and ‘‘time independent hazards’’