The New Marais Blast was a catastrophic explosion caused by the activation of a prototype Ray Sphere, perpetrated by Joseph Bertrand. It was done at 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 (prostitutes and beggars, to identify a few) at a wide secluded area at the New Marais swamps. Having set up a metal emplacement encasing the Ray Sphere at the center of the area, Bertrand activates the device and drains 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 girl named Nix, who were affected by the explosion, were the only people left in the destruction. Both left the area with 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. She'd use this to her advantage, often lurking around the swamps, taking out the Militia as 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 Corrupted.
Nix would later return 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 has if Nix had that much power when she's only stayed at the side of the Blast. After this, Nix admits that she showed Cole that just to prove that it was real, and also thought that Cole would understand best. She also explains that she wants revenge on Bertrand because the blast killed the only family members that she had. Cole then promises to capture Bertrand as payback.
- The Blast crater isn't present in the game, only appearing in the cutscene.