Why is there so much lava in my underworld when i go into hardmode?

So I beat the wall of flesh in expert mode, and I decided i wanted to start farming him. But when I went back to hell, tons of buildings were flooded with lava, and some was on my bridge. When I looked on the map, the lava appeared to be floating. Maybe blocks get removed when corrupted and they let a bunch of lava down? I suspect the save just got corrupted, but if anyone knows why this is happening, please tell me. Thanks.

Solution 1:

In expert mode, when Hell mobs die, they will leave a block a lava. It's just an expert mode thing. I made holes in my skybridge every other block to let the lava out. Try that if the lava becomes a problem.