There's some debate as to whether this is the ammo dump at FOB Falcon or a previous ammo dump explosion.
The dark material is believed to be vaporized depleted uranium.
LATE CORRECTION: That video does appear to be from a previous ammo dump explosion at Kirkuk.
The following links (1st from Arab TV) are for the FOB Falcon explosion.
http://www.youtube.com/watch?v=LlM3BDojdLo from Arab TV
http://www.youtube.com/watch?v=rEe7WjUi3hs from Euro News