Landslide and Lake Costantino, metamorphic rocks, garnet and muscovite schists. It was the night between 3rd and 4th January 1973, when over 20 million cubic meters of ground came off from the east side of Mount Antenna in the locality of Costantino from an altitude of 1230 m above sea level, where are still present today the ruins of an ancient monastery of the 10th century, and due to translational sliding of debris and soil reached the Bonamico river going up on the opposite side and thus occluding the river bed with a natural dam.
The newly formed lake was 7 million cubic meters of water, 18 m deep, 2.4 km long and 5 km perimeter, but only one month later was drastically reduced due to a further flood. The first scholars who intervened gave only short life to it due to the continuous contribution of debris from the 29km long watercourse, and soon the lake bed was filled up. In 2013, a flood re-established the normal course of the river, canceling a true naturalistic oasis, destination of migratory fauna and visitors from all over the world.
