Revealing mistake: When Rachel dies during the major earthquake, the steam goes back into the hole perfectly. The steam's movement, which is unnatural, shows that they blew steam out of the crack and then ran the shot backwards. (00:27:50)
Revealing mistake: When the fire truck gets hit by a lava ball and flips over, you can see two smoke plumes coming out the bottom of the truck. These are the remains of the two cannons used to flip the truck over. (00:34:55)
Revealing mistake: When the fireman goes to enter the fire truck that is on its side to rescue his friend, for whatever reason, the filmmakers sped up the film during his entry into the truck, it looks really out of place. (00:40:30)
Answer: Lava is extremely hot. It heats the air above and around it to such a degree that it can reach the flash point of various items.
Greg Dwyer