The recent Chinese earthquake (70 thousand dead) took place in a mountain range that abuts a densely populated (600 people/sq mile) plain. Many rivers flowing out of those mountains are blocked by numerous landslides, which according to landslide expert David Petley are very tenuous. The loose soil damn creates a lake behind, soaks through and collapses or it over-tops and fails or another landslide into the lake creates a wave which over-tops the damn and it fails. At that point a wall of water heads down stream destroying further landslide damns as it goes along with everything else it encounters.
A huge landslide damn and lake in China unwound over the last few hours and amazingly the Chinese appear to have managed to orchestrate it’s collapse so the worse case scenarios were avoided. It’s been amazing to watch the story unfold on David’s blog. Reading between the lines over the last week I certainly got the impression that he was extremely sanguine about their ability to pull this off.