[[ I may be 100% wrong on this, but ...
I think it’s French culture to bury people above ground in stone structures. Paris cemeteries are often built like this. New Orleans cemeteries are sometimes built like this. If a flood hits a cemetery it may not be difficult to damage the structure and push the contents out through a hole in the wall.
But I’m not sure that’s the case. ]]
It’s done because in some areas you can’t dig there and not hit water .
I remember standing in New Orleans by the river as a little kid where the ships move in and out and it looks like you are sitting in a hole looking up at the ships .
He conceded that the water tables are fairly high in New Orleans; it IS below sea level, after all. But he said that actually contributes to more rapid decomposition of the body and the casket, so that the idea of rotting coffins popping out of the soggy soil is alarmist nonsense.
Then again, I think the guide was half drunk.
I’m from south west louisiana and for at least 20 years we’ve buried people in concrete lined graves with a concrete cover. It’s very much a creole Catholic area and the only above ground graves are the communal crypts.