This from Wikipedia ( yes, even they can have a good idea sometimes ) - [link to en.wikipedia.org] - may well explain why Louisiana is having such problems with escaping gas & oil, it wouldn't take much of a downward slip to start the gas bubbling & the oil coming out of the sink-hole as they both seek weak points to escape the weight of the land surface bearing down.

Not sure how it explains the deformation of the sink-hole floor, but I have a feeling that the whole salt-dome ( not just the caverns ) and a vast area of land surrounding it ( everything South of the Interstate 10 & Interstate 12 ) has become unstable to the point that it may well suddenly sink below sea level and not in slow motion.

The article also explains why both Louisiana is sinking & the sea floor in the Gulf of Mexico is rising.

This link may help too - [link to www.chron.com]