This is a must read article from EW - here’s a snippet:
Did you even know there was a volcano on the ABC series Lost? It’s true. And it might have made a bigger impression — and led to a different series finale — if not for a small matter of money. The presence of this geographical feature on the show’s mystical, time-skipping island was established in season 3. You see drawings, images, and even a model of it in a Dharma Initiative classroom. Obsessive viewers spotted it and theorized about it, but when Lost never returned to it, fans assumed the volcano was a red herring or rich bit of detail. Actually, it was one of the first hints of an endgame.
Carlton Cuse, Lost’s longtime co-showrunner, got the idea for the volcano in the early years of the show after visiting Hawaii’s Big Island with his family, taking a volcano tour and marveling at the landscape. He thought it would be cool if The Island had a volcano of its own. “We were always looking to cannibalize anything on Hawaii to aid in the visual storytelling of the show,” says Cuse. “We also thought of the island as a character on the show, so we were always looking for things that would give it more personality.” He didn’t have an idea of how the volcano could be used, “but it was something we banked and thought we could use downstream.”
The volcano stayed in the back pocket until the producers started developing Lost’s concluding seasons. The premise that developed over time was that the volcano was a mysterious place that forged the ticking, shape-shifting monster, the billowing black mass known as Smokey. By season 6, the writers had settled on the concept that the island was like a cork that bottled up all sorts of bad stuff, some volatile stew of spiritual dark matter stuff that would rob life of meaning and goodness if unleashed. “The question was always, how do you basically visualize and dramatize the idea that the island itself is all that separates the world from hellfire and damnation?” says Lost co-creator Damon Lindelof. “And the answer was the volcano.”
