Thanks to Ivan Montanari for highlighting this one. Youtube has an extraordinary video of a debris flood that appears to have occurred yesterday at Atrani on the Amalfi Coast in Italy:
The video makes a slowish start, so keep watching. This is the first debris flow of cars that I have seen on video...! This is a Google Earth perspective image of Atrani:
I guess it is not hard to see how very heavy rainfall, or another hydrological event in the catchment, can lead to such an event.