The New Marais Blast was a catastrophic explosion caused by the activation of a prototype Ray Sphere, perpetrated by Joseph Bertrand. It was done in the far off swamps of the city, to minimize the casualties and to keep the act secluded from the public.
After running tests for the Ray Sphere by Sebastian Wolfe, Bertrand had prepared a large amount of lower class citizens such as swamp dwellers, beggars and prostitutes at a wide secluded area in the swamps outside New Marais. Having set up a metal emplacement encasing the Ray Sphere at the center of the area, Bertrand activated the device and drained the dormant energy of the civilians, effectively killing all of those who do not have the Conduit gene.
After the Blast, Bertrand and a young woman named Nix, who was also affected by the explosion, were the only people who survived the blast due to possessing a Conduit gene, gaining new unlocked abilities.
I just had to show that to someone. Just to prove that it was...real. You know? Figured the Demon would understand.
― Nix, explaining to Cole why she showed him that site.
After Nix left the area, she gained Napalm Manipulation, and was able to manipulate fire and oil. Using this to her advantage, she often lurked around the swamps, taking out the Militia in an attempt to keep her territory, and also take revenge on Bertrand. While Nix was satisfied, Bertrand found out that he'd turn into a gigantic monster, labeled as the Behemoth by some. He'd complain and grieve over his existence as a giant monster, and decided to spread artificial Conduits (Vermaak 88) all over the world to show the world why they should fear Bertrand's kind. Bertrand also had the ability to convert humans into the monstrous creatures known as the Corrupted.
Nix later returned to the site with the Conduit, Cole MacGrath, to show and explain to him what had happened. Cole immediately recalled the similar event from Empire City, and couldn't help but wonder just how much power Bertrand had if Nix had that much power when she's only stayed at the side of the Blast. After this, Nix admitted that she showed Cole that just to prove that it was real, and that that Cole would understand best. She also explained that she wanted revenge on Bertrand because the blast killed her family members. Cole then promised to capture Bertrand as payback.
- The Blast crater isn't present in the game, only appearing in the cutscene.