The pass was created when a huge mountain slide (actually the collapse of an entire mountain, with an estimated volume of 1 km3; the third-largest mountain slide ever in the eastern Alps) filled part of the valley to a height of 300–400 meters, distributing its boulders up to 16 km away. While it was initially believed that this had happened at least 12,000 years B.P. as a consequence of the strong temperature increase and intense run-off after the end of the last deglaciation, pollen analysis performed as early as 1940 had already indicated an age of not much more than 4,000 years (i.e., an event date around 2000 BC), an estimate that was essentially confirmed by radiocarbon dating in the 1960s. Using uranium-thorium dating, scientists from Innsbruck University who published their data in 2007 dated the event to 4,150 +/- 100 years B.P., i.e., to the 22nd century BC which corresponds to the latest stages of the Alpine neolithic period.
