From Video Game Music Preservation Foundation Wiki
Area 7 is a very rapid paced song that plays in the fiery lava tunnels.
This song is also played when you're fighting the final boss once he reveals his true self.
Due to this song's position in the NSF file, it's probable that the song was originally designed as the final boss's music, and not as an area tune. This song is track 13 in the NSF file.