A landslide occurred in the Alps near Bellinzona which is described by Leandro Alberti in 1550:
In the past years an earthquake caused a large part of a mountain to collapse, in such a way that the Bregno valley came to be obstructed; and as the river came to be dammed up, it produced a large and dark lake with great damage to the inhabitants of the valley, many of whom were drowned and their houses submerged. And so it stayed for quite some time, until the fallen earth made gradually soft by the infiltrations of the water and being no longer sufficiently strong to retain the immense pressure of it, suddenly burst open to the fury of the swollen waters. And since the former river bed, which was joined to the Ticino, was no longer adequate to contain it, the water flooded all the neighbouring regions, overthrowing in part even that strong wall which Lodovico Sforza had built near Bellinzona.
... for in our own times a similar thing has been seen, that is, a mountain falling seven miles across a valley and closing it up and turning it into a lake.