"Cemetaries in N'awlins are above ground. Alot of flooding
and, well.. you know."
Flooding is the very reason the crypts are above ground.
Before the above ground burials they used to get corpses washing out of the ground every time it rained hard. Gruesome to consider, but that's the way it was.
The bodies are safer all encased in concrete and above ground.
"The bodies are safer all encased in concrete and above ground."
Lots of graves are totally encased in concrete crypts, but far from all. We've got two family burial plots in NO; ours and many others are more like concrete, hollow, open-topped boxes that are filled with earth. If it floods like they say, there will be some corpses floating around eventually.