Factual error: The volcanic ash that can be seen throughout the film is too big to be real. The ash shown is something like 1-2 cm in diameter. Volcanic ash is not that big in real life; it is not more than 2 millimetres in diameter. (01:02:30)Ssiscool
Factual error: When lava engulfs the streets, aluminum light poles do not melt (it has a melting point of 1,212° Fahrenheit), yet entire vehicles with steel frames melt into the flow (steel melts at 2,750° Fahrenheit). Lava reaches around 2,000°.
Factual error: It is impossible for a volcano to form under Los Angeles. The San Andreas Fault traveling through the west coast is a "Transform" fault in which the Pacific plate and the North American plate creates a fault line that only slide past each other. In order for a volcano to form, two plates need to subduct. Because there is no ripping apart or subduction taking place along a transform fault, there isn't any magma formation to lead to volcanoes.
Character mistake: The downed firetruck was referred to as engine 17, however it is actually engine 23.
Continuity mistake: When the lava begins spilling from the tar pits, Tommy Lee's SUV is not parked next to the pits, but after the downed firetruck shot, the SUV is now there.
Factual error: Mount Wilshire is basically a shield volcano in the form of a tall stratovolcano because shield volcanoes only shoot ashes, gas, and lava (and pyroclastics for pyroclastic shield volcanoes). The lava itself behaves as if it was sentient. During the lava geyser scene, small particles of molten lava seem to be falling directly on people despite the fact that no-one was anywhere near it except for Mike, his daughter, and the little boy.21collaw