This is a video from New Zealand of a granular flow of rocks pouring down the side of a hill near the Rakaia River in Canterbury. What the hell is a granular flow? Let me copy/paste that for you while I down a bottle of DayQuil because somebody got me sick again. I blame the hunk at the gym who was using the eighty pound dumbbells before me. "Eighty?" Ten.
This is a magnificent example of a granular flow. Whilst they appear to be very exotic, granular flows are quite common and have been well-described in the literature. In essence the pebbles behave as particles, allowing behaviour that is akin to that of a fluid. Of course the density of the fluid is somewhat higher than that of a more familiar liquid, such as water, and the particles are many times larger, but the river of rock is still able to generate the sorts of flow structures that we see in water...I suspect that this one comprises particles that are of a comparatively even size--Simon Cox from GNS suggested to me that the material is probably greywacke. It may be that this uniformity lies behind the unusual characteristics of this flow.
Crazy, right? That is not a river I would want to skinny dip in -- those rocks look like they could really tear a pecker up. Now fishing, fishing is another story. What kind of fish do you think you could catch in there anyways? "Rockfish." Wow, you really didn't try too hard, did you?
Keep going for the video.
Thanks to SN, who wants to know if it's possible to skip a rock across a river of rocks.