Plot hole: After the volcanic eruption, there's a scene where we see our heroes going across a lake, which has been turned to acid by the lava. If this acid is strong enough to corrode the propeller, then surely the fumes would be destroying their lungs, in which case they should be dead, or close to it.
Plot hole: After the pyroclastic explosion Rachel, Harry and the kids get into the mine. There are a lot of things from Rachel's son in there: Sodas, chips, tapes and a tape player/recorder among them. There is a shot in which we can see a pile of tapes on the player, in almost perfect order. But if we consider that the whole town collapsed because of the earthquake occurred before the eruption, then those tapes must have fallen down, surely?
Plot hole: Rachel calls a town meeting for 6 p.m. to discuss evacuation, about 8 hours after the danger became apparent. Wouldn't it have been more responsible to call the meeting earlier in the day, to keep the town on alert to get the hell out of there?