I was listening to NBC news and they said they think it hit an Iraqi amunition compound, therefore the loud explosion.
Nonsense: Ammon dumps explode in long serious of small and medium explosions: how are the shells and explosives going to go off at once? At Khe Sanh, one ammo dump was hit, and it burned/exploded for hours afterwards. Same thing at an airport near (I think) Hue earlier, and also at Da Nang. See also the Israeli & Egyptian dumps going in the 73 war.