July 28, 1987 Tsunami: Valtellina, Italy

The 28 July Val Pola landslide (Lombardy, northern Italy) claimed 27 lives and a total cost of about 400 million euros including destruction of villages, road closure, monitoring and warning systems, construction of permanent outlet tunnels and earth movements […] Between June and July 1987, Valtellina was hit by an exceptional meteorologic event. About four times the average rainfall for the area felt between the 15 and 22 of July […] On 28 July at 07:23 AM [local], a volume between 34 and 43 millions of cubic meters (according to different estimates) detached from the slope. It moved rapidly down the western valley flank to reach the valley bottom, raised for 300m on the opposite valley flank and flowed both upstream and downstream along the valley. […] The upstream movement was characterized by a large mud wave, up to 35m high, that reached a distance of 2.7 km whereas the maximum distance reached by the debris was about 1 km. (reference #14094)

The Valtellina in Northern Italy was deluged by more than 600 mm of rainfall in mid-July, 1987 during a period of exceptionally warm temperatures […] On July 28, 1987, a rock avalanche with a volume of 35 million m3 collapsed into the Adda River valley, catastrophically displaced the water in the Val Pola debris-dam lake, and ran up 300 m on the opposite valley side. The avalanche sent a wave of water and sediment 2.7 km upstream, damaged three villages, claimed 27 lives, and dammed the Adda River valley. Using the apparent friction coefficient of the rock avalanche of 0.36, and the run-up height of 300 m, the Val Pola rock avalanche moved with a maximum velocity between 275 and 390 km/hr, placing this landslide among the most rapid mass movements ever documented […] Erosion and mud marks on the west valley wall upstream from the landslide indicate the wave was initially 95 m high a short distance up stream from the original site of the lake, and about 15-20 meters high at a distance o 1.3 km upvalley […] The greatest loss of life in the Val Pola landslide (20 deaths, three villages destroyed) was caused by the rapid displacement of water from the shallow debris fan-dammed lake previously described. Early reports from Valtellina attributed the casualties and destruction upstream of the Val Pola rock avalanche to high winds caused by the high-velocity rock avalanche (WARREDOC 1987: 13). Later field work documented that damage and death resulted from a large wave from the displaced debris flow dammed lake […] The Val Pola rock-avalanche disaster response, monitoring system, and construction activities have cost an estimated $400 million (reference #14095)

The north arm of the rock avalanche displaced the water of a preexisting landslide-dammed lake, generating a wave that killed 22 people [at Aquilone] more than 2 km upstream (reference #14096)

On July 28th early in the morning, 35 million cu. m. of rock collapsed. sliding along the two main joints. The huge rock mass moved north and hit the spur located beside the Pola River and then slid east generating a rock avalanche […] The rock avalanche went up the opposite slope reaching an altitude of 1,350 m. A wave of water and mud running up hill (North), was caused by the landslide impact on the lake formed by the Pola debrisflow. The villages of S. Antonio Morignone, Poz, Tirindre and part of Aquilone were swept away by the mud wave. (reference #14097)