...why New Orleans' burials are typically above ground, this should clear it up.

I took this photo in McDonoghville Cemetery in Algiers- still in New Orleans, but on the far side of the Mississippi. They have a mix of semi-in ground burials(called copings) and traditional tombs, and this is a new coping that had been dug but not yet lined.

You only have to go down 12-18 inches before you hit water- New Orleans is basically a skim of soil atop a lake. Even the graves that seem to be closer to the more usual American-style aren't all they appear.

This hole will be lined in cement block and sealed, but how well that sealant works is questionable at best- here's another nearby grave that's further along in the process, and still had several inches of water inside:

I should point out that it's been a particularly dry season here- it hadn't rained in over a week before this was taken.

Ultimately, the site will look much like this:

It will be capped off with a material of the family's choosing- typically cement, or heavy boards weighted down/covered over with gravel- and in the end the bodies will really be partially above ground after all.