The Val Pola Rock Avalanche occurred on July 28, 1987. A total of 40-50 million cubic metres of rock were mobilized after a period of extensive rainfall. Besides destroying a number of villages and claiming dozens of lives, the landslide impounded a lake and reshaped part of the upper Valtellina. Extensive works were carried out to create a channel for the Adda River through the landslide deposit.