I spent a week clearing this crap out of people back yards with the student army of volunteers. They estimate 200000 tonnes of the silt had to be cleared.

Here's an example of the silt coming out of the ground minutes after the quake. http://www.youtube.com/watch?v=e_twYpUJl9o

And here's a good explanation http://mandenomusings.wordpress.com/2011/03/03/christchurch-...