Hey Kai, you bring up a really interesting question. Personally if we're talking Canon here, as in the Show, I think only fire-benders would be able to bend lava. For the simple reason that Mike and Bryan never delve too deeply into the science of things. Lava, Fire. One thing I have noticed though, is that Fire-Benders rarely take pre-existing fire to bend. They usually make fire themselves, and create their own flames even if there's already fire around to bend. Also there's the infamous 'heat syphoning' to think about. Which makes me wonder about how exactly fire benders work. But looking on the theoretical side it makes much more sense for Earthbenders to bend Lava. There is no water in lava so I don't belive Waterbenders could do anything with it.

However if I were to simply attempt to explain that image of lava bending you have posted I'd have a much easier time.
I think the avatar in that image is simply superheating the volcanoes to cause them to erupt. Plenty of Firebenders have created heat, it just depends on wether or not the Avatar can create heat at a range or not.

That's my two cents I suppose.
The image makes since. Any mechanics of lava bending escape me completely

Whoa, what a fantastic idea for a discussion Kai. Honestly I'm stumped. But many of my reasons and thoughts lie within what Auka was saying. I don't think a waterbender could ever bend lava. Yes it does flow and to many it looks liquidly but for me personally I could only see a firebender controlling it or even an earthbender. But then I look at the facts, lava is in fact molten rock. As I look at pictures of it now I actually think that only an earthbender could bend such material. It is very dense and even in its hottest state it still looks rock solid. Maybe firebenders could use volcanoes as sources of heat, and I agree completely with what Auka suggested about the image. I think the man in fact was only heating up the volcano in order for it to erupt.

I like what you've suggested about an earthbender with the training of a waterbender, but I think that a dead on earthbender would be capable in using this material to his/her own advantage. Perhaps a firebender could use flames which spurt out of the volcano, but aside from that firebenders do usually create their own fire. Oh... then again... an earthbender may not be capable of bending lave due to it's high and burning heat. I'm not sure if it's possible for earthbenders to bend earth that is that hot. Maybe there is a certain temperature at which even earthbenders are limited at bending the earth. Rock is easy since it is not too hot or cold. I mean mud is liquidly, but like a rock it isn't hot nor cold. I'm positive that an earthbender can't bend ice, it's far too cold and frozen.

Epiphany! No one can bend lava, at least I don't think soo. Just like ice is too cold to earthbend, lava is too hot. Firebenders can only heat up such material to cause explosions and since there is no water in lava it's impossible for a waterbender to do any type of bending. Wow I've gone back and forth haven't I?

That's where I stand now. No one =]

My inner volcanic geologist was cringing when both replies said that there was no water in lava, but that's real world science and not Avatar. Also, if volcanoes in Avatar work anything like volcanoes in the real world, the eruption is fueled by gas exsoluting and expanding due to a decrease in pressure, not head.

In regards to Shuai's comment about an Earthbender bending ice, they wouldn't be able to, as ice is water. However, if there was rock under the ice, an Earthbender would most certainly be able to bend it.

I'm a little unsure of how temperature affects bending. With Waterbending, one can create ice or fog, but not steam. I believe that an Earthbender would be able to bend lava, but it would be highly dangerous considering that lava is extremely hot; that's why a fully-realized Avatar would be able to bend it. He could use a combination of Fire/Earthbending and have the Waterbending knowledge to put it all together and bend lava.

Haha I just realized how odd my ice comment was. I mean I understood that ice was water, but for some reason I was picking things on Earth that earthbenders would be unable to bed and then suddenly I thought, OH ICE. So yeah, disregard that little mishap. And yes the whole gas starting the eruptions of volcanoes does kill the Avatar idea of just heating them up. Stinking real world getting in the way of cool Lavabending. And if there HAD to be one person who could let's say Lavabend I'd also have to agree with you Kai. Fully-realized Avatar ONLY. With my temperature comment I did mean to say that it would be both very dangerous and insane for earthbenders to bend material that can get as hot as 2500 degrees Celsius. I just think the heat would be far too much for an earthbender to handle.

So... alright... maybe there could be Lavabending, but It would have to be done by a VERY experienced Avatar. Still I'm a little iffy on the matter, but this is Avatar. Many outrageous things can be done xD

I would like to point out that while volcanoes DO erupt due to high pressure, I would ALSO like to point out that as you increase the temperature of a substance, either the volume or the pressure must increase. There are niffty little equations for it and everything. So, super-heating the interior of the volcano, which can be combared to a stoppered glass beaker with water in it, would eventual cause an explosion through the weakest point in the system (traditionally the top of for volcano/were the stopper is in the beaker). Please no one blow up glasses in their kitchen and blame me.

Moving on to the actual subject, and its current biggest road block of heat. I personally can't really recall any instances of extreme range earth-bending in the show, most of it at least starts within reach of the earth bender, which would prevent most lava bending. However, I do remember a scene in the first season where the earth benders manipulate coal in a prison break, including using it as a shield against fires. The coal then becomes red-hot, but they still use that coal to bend with. The coal was a solid dark black, which implies (to me) Anthracite Coal, the hottest burning variety (others are more towards the brown color). Lava, however, is liquid at 700 °C to 1,200 °C (1,300 °F to 2,200 °F) while Anthracite burns at around 2000 °F when done properly, which means that heat should not be an issue. At the very least, it can (and frequently does) melt steal or cast iron, the iron melting at right around 1400 °C.

From that, it can be reasonably assumed that any Earth bender (or more likely a sand bender or something) could bend lava from a distance if they went through the trouble of finding out how it would work, akin to Toph and metal-bending.

One also has to take into account that simply making a volcano erupt is not Lavabending, as they're not manipulating the lava itself.

I think that after much thought, I'd definitely have to give it to the Avatar. Sure, an Earthbender could bend lava (as they can bend any earthen material, as well as meteor rock), but they would lack the fine control necessary to bend it effectively (or in any way other than blasts of lava). Since the Avatar would know how to bend water as well as earth, he could incorporate smoother and more graceful motions to effectively manipulate the liquid nature of lava while still bending earth.

Oh, and increasing the heat in a volcano would indirectly increase the pressure inside by causing more gas to exsolute from the lava. It would, however, effect the viscosity of the lava itself. (I won't go into the boring details)

Hehehe I will be the debbie downer of this thread since I still think that NO one can Lavabend, maybe besides the Avatar, and taking in what everyone has said I will reach my conclusion.

How about no Lavabending? I mean heck, the creators were nice enough giving the characters four elements xD Must we have five? -NEVER- we like even numbers =] Yay fire, water, earth, and air. Lava you are uncool and by me band... forever.

I hope my little rant has in some way shape or form made you smile, if not I fail at life and will continue on... As I was saying I really think it impossible to Lavabend. I mean I can't give you a certain answer seeing as how I'm not a scientific genius, thus not knowing enough about volcanoes and how they work. I do appreciate that information of yours Tianli, about the episode where the earthbenders used the coal and how it was heated and what not. But again going with what Kai said, I'd only leave it up to the Avatar to do such bending. I mean, maybe Toph could have a shot, seeing as how she is the wicked earthbender who created Metalbending. Maybe she can create Lavabending. Who knows?

-snickers- I still say eh to the whole idea of Lavabending. The idea of it is cool, the actuality of it seems harder than bending the basic four elements, which should still surprise people xD I mean if I could move water or shoot fire out of my hands, I'd be happy =]