Describing its music as “swamp-metal,” the Savannah, Ga.–based trio Black Tusk opens its third studio album with “Witch’s Spell,” a 57-second instrumental that layers the band’s hard-driving sludge rock over gurgling samples of what sounds like a bubbling cauldron. But the following “Fixed in the Ice” is what really ignites Passage Through Purgatory. Andrew Fidler screams in a raspy high tenor (reminiscent of the late Sam Kinison) over the eardrum-assaulting blasts of a guitar rig cranked to 11 and a rhythm section flying off the rails. “Mind Moves Something” plays with a similar hardcore punk attack and Southern-steeped sludge, which sounds as if High on Fire were fronted by a Dixie flag–flying Ted Nugent. Drummer Jamie May and bassist Jonathan Athon downshift into a slower-galloping time signature for “End of Days,” sounding like the Four Horsemen of the Apocalypse as May chants battle cries while pumping his guitar through a sinister-sounding effects filter. May’s rapid-fire riffs blend with the rhythm section’s heart-attack pace in “Prophecy One by One” to create an anxiety-building epic.