Luck? The angle of impact? Some inherent flaw in the masonry of one compared to the other? Some variation in the power of the Killing Curse used?

It seems almost conspiracy-theory esque to think Dumbledore planned for it.

I don't think so. If he could have, he would have. The reason why he didn't is fairly clear from the text: he was distracted in banishing the snake Voldemort had transfigured, and it was too late for him to change what he was doing at the time the Killing Curse was inbound.

He emptied the plinth because he animated the statues as protective guardians. There was no 4D chess where he somehow knew how the duel would go. He isn't a seer. It just worked out that way, but it could have gone a hundred different ways, depending on what spells Voldemort had chosen to use.

He wasn't duelling to prove he was the greater wizard, but the fact that he needed support is telling as to who is the greater wizard.

Sometimes you miss. Voldemort also missed in the graveyard against Harry.

Also I severely doubt the accuracy of spells has anything to do with physical position/orientation. It's not like spells are shooting out of the end of the wand like a projectile.

 

Oh, I just said that because I remember him missing when he went after Harry in the Seven Potters scene in Deathly Hallows. So that may have been because he was flying and unable to focus perfectly or something. If he missed in the graveyard, fair enough.

I based it on the assumption that Dumbledore could imbue the statues with resistance to all curses, which is why the witch and wizard weren't destroyed, and the centaur breaking apart was because he meant for it. Perhaps not a great conclusion, but the only one that occurred to me.

Any idea why the Killing Curse failed to destroy the statues, though?

Fawkes appeared before Voldemort even apparated to the plinth. I'd say he knew the curse was coming, and that Voldemort was going to appear somewhere, and summoned Fawkes to make use of the opportunity. He could've apparated out of the way of the snake and on the far end of the hall, banished the snake, and apparated again to avoid the curse, It would just get him back to the way the duel started, however, with no one getting the upper hand. And Voldemort might figure out how to get to Harry in that time. So, rather than apparate, he used Fawkes. Voldemort would feel triumphant for a moment, and in that time Dumbledore would spring his trap (in case of appearing on the plinth, using water).
Again, just a theory. Any holes, point it out.

 

I guess that's because you need 'an act or valour' or something to use the sword? Harry was quite certain Ron had to destroy the locket using the sword.

 

With regard to the sword, I'm happy to defer, but he did leave it with someone he trusted to deliver it - Snape has it. As far as I'm aware, it's Snape's choice to hide it in the lake, although equally, he can't really deliver it face to face because Harry 'knows' he's a traitor, so the point about that knowledge arguably still stands. There may have been a different plan to get the sword to Harry if things had been different though, and Harry hadn't been on a camping trip.

Also, with regard to Dumbledore duelling, he is somewhere between 115 and 150 years old, whereas Voldemort is about 70.

 

Spells quite often bounce off physical objects, and sometimes break physical objects, generally in an unpredictable manner. See e.g. HBP:

I disagree in a number of respects - some of which are repeating previously points, which I don't think this answer adequately rebuts.

1. As a general point, I disagree as to the nature of Dumbledore and Fawkes' connection. Dumbledore does not command him, nor do they share some sort of telepathic connection. Fawkes' arrival, I think, was entirely something of Fawkes' volition and discretion, not something Dumbledore could have known about or relied upon. So from the get go, the whole idea of Dumbledore planning for Fawkes' intervention seems like a non-starter.

2. The sequence of events just reads as inherently very implausible. There are far too many factors and variables for Dumbledore to account for in such a way, without weirdly accurate Divination. And on top of that, we're talking about something that happened in less than a second - there's no way Dumbledore was able to process the snake, the incoming curse, and plan all of that in the time he had, while also casting the magic he was casting.

3. I disagree there was any trap, for the reason given above re "clearing the plinth" conspiracy reasoning. He took opportunistic advantage of the water, and if Voldemort had done something else, he would have taken opportunistic advantage of something else. The duel was far too fluid to anticipate that outcome (and also it's not like the use of the water was particularly special, given that Voldemort was able to escape it just fine).

Another point in Voldemort's favour then, given that Dumbledore had the age advantage?

Their physical conditions don't seem to play any role in the duel, and logically, there's not really any reason why the physical condition of the participants would have any impact on a duel at that high level where magic is basically used for everything.

 

Worth noting that neither of the killing curses was intended for the statues.
The first was intended for Harry

While the second which destroyed the statue was intended for Dumbledore

I wouldn't be surprised if Voldemort was simply more focused when attempting to kill Dumbledore than he was with Harry, whcih likely resulted in a stronger killing curse capable of destroying the statue.

 

Yes, I suppose a psychic link cannot be considered, since we don't even have any evidence of that, unless the circumstances are beyond weird (Harry and Voldemort).

Still, I believe Dumbledore knows that Fawkes would come if he was in trouble - if Fawkes appeared just because Harry showed loyalty to Dumbledore in the Chamber of Secrets, then he would surely do so when Dumbledore himself was in trouble. So, Dumbledore can still go completely on the offensive(while not focused on defending himself completely, because he has a surprise defence) till Fawkes intercepts one curse, which he did seem to do - Voldemort's attack was sudden and unexpected, because until then, he seemed to be on the defensive.

And Dumbledore knows this, so yes, I'd say he could rely on Fawkes, just not the way I originally said. This is just him making use of an advantage he has. Otherwise, the duel could stretch too long, and that only gives Voldemort a greater chance to kill Harry (He's the Heir of Slytherin(and not just by blood), so I'd assume he has to be cunning enough to pull it off). And a bunch of other people, because it would be just as legendary as Dumbledore and Grindelwald's, and Voldemort has shown ability to curse others during an ongoing duel.

(By the way, do know who said Dumbledore and Grindelwald's duel took 3 hours? I've read it a bunch of times, but I don't know if it's actually stated by JKR).

Fawkes came before Voldemort even reappeared - so it's fair to assume Dumbledore knew a curse was coming. And he also knew Fawkes would take it for him. Otherwise, he'd have apparated from there. It'd give him breathing room. Again, that would only make the duel stretch longer.

My apologies for using the word 'trap'. It was quite inaccurate. But when Fawkes took the curse, Voldemort would be caught by surprise for a moment, which is why I think the use of water worked. Similarly, if he'd just appeared somewhere else in the Artrium, Dumbledore would land another attack, and since Voldemort managed to escape the water, Voldemort would escape the other attack as well.

Also, if we consider the verbal exchange between Dumbledore and Voldemort, where Dumbledore says merely taking Voldemort's life won't satisfy him, also suggests that they both considered Dumbledore superior. This isn't particularly sound evidence, however, and I was only obliged to state this.

Edit: I read what I wrote again - there is no evidence that Dumbledore was the superior wizard in the duel. If Dumbledore knew Fawkes was coming, then the duel is inconclusive. We don't know how else the duel could've progressed if he wasn't duelling with the knowledge that one deadly curse would be intercepted.

Possible.

 

Regarding their ages, I don't think Dumbledore's relatively advanced age made any difference.

Considering he's doing a perfect breaststroke in the ocean which Harry describes as icy with one hand withered away, I think Dumbledore's agility is more than fine.

The statue which breaks was also animated along multiple other statues. I expect that the statues would be weaker than the statue animated on its own as a result.

I think Voldemort is clearly Dumbledore's better in a duel. Dumbledore has the elder wand. Despite having the wand, Dumbledore still has to rely on Fawkes to defend him.

With that said, it does seem expected by Dumbledore. Though it may not be some sort of "psychic bond," Dumbledore is defending against the snake and attacking Voldemort at the same time that Fawkes is eating the killing curse. I would have expected a two-fold defensive action against both attacks instead if Dumbledore had not anticipated Fawkes' involvement.

With that said, I disagree that every high-level duel reflects all knowledge and intimacy with magic. I think it's clear Dumbledore has a much better understanding of wand lore and sacrificial magic than Voldemort, but I highly doubt it came into the duel at all. I do think Dumbledore holds an overall edge in terms of breadth of knowledge.

 

Eh, you definitely didn't read the books. It's explicitly stated that he doesn't fear Harry, and thinks Harry has survived time and again due to luck, the intervention of his betters, and Voldemort's own missteps. In HBP it's made abundantly clear that Voldemort absolutely hates Dumbledore and that Dumbledore is one number 1 on his to-kill list.

 

As I recall, Voldemort said those things in front of a group of his followers in the first chapter of Deathly Hallows. That's not an audience where he'd confess to fearing anything, and we know he feared a ton of things. That whole bit can easily be dismissed as posturing given the circumstances.

 

I mean, we do see his thoughts after finding out Harry stole his Horcrux from Gringotts.
While he is terrified about his secret coming out, he mentally associates it entirely with Dumbledore and he starts theorizing how Dumbledore could possibly find out about the location of the other Hocruxes, Harry in all this is a mere afterthought.