I want to traumatize / hyper engage my players. The Fall of Elturel will be the big hook, which takes the player out of the "trainee" levels and into the heart of the campaign.

I have a lot currently fleshed out, but I want to really make this a big climax in the story. My players start their journey in Elturel rather than Baldur's gate. but essentially go through mirror versions of the dungeons outlined in the first chapter of the book. the plan is to manipulate / trick them into triggering events which will lead to the gates of hell opening up and swallowing the city whole

While preparing, I've find I struggle most describing the actual cataclysm itself. I need an visual or literary reference for my brain to use as fuel for when literal hell breaks loose.