Thanks to my former student Kurtis Garbutt for the heads up on this one.  The video below shows the progressive development of a road in Thailand.  I suspect that this initiated as a culvert failure, with multiple collapses due to undercutting:

The final frames of the video show an overview of the site.  Check out where the people are standing!

As an aside, Kurtis also runs a very interesting blog on natural hazards – take a look.  It is a very useful resource with a scope that goes way beyond my site.