You might well wonder why a merciful God wouldn't simply destroy a soul rather than plop it in some vile realm of torture, hate and madness? In asking such a question, you've wandered right into Annihilationism, the Christian theological notion that souls are not inherently immortal. This leaves God the freedom to grant immortality to the saved souls and to simply punch "delete" on all the rest.
So in this, Hell is either a process by which a human soul is destroyed or the instantaneous act of destroying it. It's rather the opposite of a universalist's temporary Hell, but still far more merciful than the old everlasting fire model.