Talukita said:
There are several ways to argue against this:
1. The lava is created by magic, not real lava, hence not as powerful. This pretty much applies to everything in FT really. The black hole that Gildartz crashed is nowhere near a real black hole (or the story would have ended at that time), it's just a stronger magic overpowered a weaker one. Stronger fire mage creates stronger flame, stronger ice mage creates stronger ice when they are both... ice. Hell Gray was able to freeze flame which is impossible with physic. Can give tons of other examples here (Laxus' lightning. Sting's laser breath, etc). Additionally, seeing this lava is only a branch spell of Tai's Terrain magic, it being weaker is nothing surprising. I can see this is the reason why most of Mashima's manga revolves around magic, because it's quite easy to avoid plotholes/ law of physics by simply using "It's fucking magic, duh"!
2. There is still a possibility that Arcadios is a very powerful mage, yet want to hide his power (to bait Lucy for the Eclipse plan, etc). And we all know that all high tier mages of this series have extremely high durability (probably because of the magic boost), this combines with the first one making him being able to survive in the lava become quite natural.
All good points, and I wasn't saying that there's no way he could survive etc, but just the reason that I was shocked that he did. General consensus on lava is, well, death. And yes, I'm truly hoping for something like #2. Otherwise, his survival is a cop out to me.