Mt. Piping Hot Suckhole is used by Big Jo to kill Demons. Luci's Lawyer, Stacianne LeBlatt along with others were thrown into the lava here. The lava likely has mystical properties, as demons are immune to fire, which means they are probably immune to regular lava as well. There is a height limit to sacrifice, and Big Jo would have broke that rule if he had not been killing for other reasons.