Gandalf Theory
Heres an interesting theory to describe something that was never very well explained in the books....
When Gandalf fights the balrog in Moria I think there is a lot more going on than we see. I think that when G visited moria the first time he got a vibe from the bridge of khazud-dum and had a vision that he would face a great challenge in this place at some point in the future. So, he did something very wise....
He encased a large amount of his powers into the bridge so that he could call them back at a later date. This would explain why he looked so shabby and grey and was white and magnificent when re returned.
So, when he met the balrog and smashed his staff into the bridge he was actually calling his power back from the bridge to enable him to kill the balrog. This would explain the white flash we see. Gandalf the Grey to Gandalf the White.
What do you think?...
Yeah, I have read the books, palanfirith. Its just a theory. It could still work because he would still be half dead after the battle, he just needed the extra power to defeat the balrog. If he hadn't stored his power he may not have survived the battle.
This theory would also explain the sense of dread he had when he realised they had to go through moria.
My theory
My theory is that the Valar required that the Maia (Wizards) always have a chief who wears white.
Gandalf, knowing of the treachery of Saruman, and having a sense of what was to come in Moria, knew that his ascent into the position of Head of his Order was only going to be accomplished with a "test of fire" (so to speak)and the need to replace a fallen "Head of Order". He knew that this would happen...he just was not thrilled about the timing...during the quest.
Just a theory
Sorry folks the truth is out there(read the book)!
you see gandalf was killed(his mortal body) and his spirit was sent back(from the west) until his quest was completed.
The same happened to another person in silmarilion(glorfindel)!
He would have to have made the same mistake as souron if he did put his power in the bridge?seems unlikerly that he would