Les catastrophes naturelles de l'été 1987 en Lombardie : crues,inondations, écroulement de Val Pola

摘要

Abstract. — Heavy rains in the Italian Alps in the summer of 1987 (July, 14th-21th) gave rise to a number of disasters in Valteline and Val Brembana : floods, droughts, debris flows, rock flows, landslides, rock falls, ... Huge movements of coarse materials in the rivers and along the slopes occurred and these disturbed the spreading and the flow of waters. In Valteline, the rock-slide of Val Pola (30.16 тъ) can be explained mainly by the morphological features of the valley, correlated with the glacial and post-glacial evolution : glacial bench infissu- rated rocks, rock decompression, post-glacial deepening of the valley floor by the river Adda. The sliding was induced by the rains of July 1987 and by the underflow. The Lake of С ото variations during this period lead us to conclude that the amount of precipitations in high mountains areas was about 400-500 mm. The flooding was worsened by the melting both of a thick snow cover (10-20 cm) and of a thin layer of glacier ice (about 20-50 mm). In the first days, the 0°C isotherm was high, over 4000 m and even over 5000 m on July the 16th. During the last week of August, lack of snow meant that heavy rains did not give rise to floods and extensive damage in the upper Valteline.