On the second map, there are some mines that you will need to explore; once you get through them, there is another underground area and then you can get back to the surface. By design, the mines get flooded with lava when you escape. Until you reload a save, the waypoints in the mine will remain in the list, and if you teleport back to the mine it can wipe out your party.
To avoid that, don't teleport back to the mine (there is not much reason to return if you loot as you go), or save and reload after getting out of the mine.
