Tim McKinney, a geographer and a Boing Boing reader, offers an explanation of what happens in soil and structures during flooding and heavy precipitation events — and one possible explanation for rumors among evacuees that the levees "were bombed."
I've tried to explain a little more, in completely nontechnical terms, some of the forces at work. What may also is how once a failure threshold is reached, the result may be a slump or a more drastic rapid flow or blowout.
I mention this in light of unsubstantiated comments posted which referred to unnamed persons hearing sounds like explosions around the time of the failure. If a levee fails abrubtly and the canal containment wall above it tears loose, it could generate a significant noise, perhaps like a rumble or an explosion even.
Link to Tim's doc (PDF). (Thanks, Kathryn Cramer)
