New today Factual error: The entire time the volcano is shown erupting, the volcanic lava is instantly melting everything it touches despite the fact that in real life volcanic lava would not have any human being melting because lava is more dense than water. Also lava in real life cannot instantly melt things. And no object should be sinking if caught in a lava flow.
New today Factual error: The volcanic lava in this movie moves incredibly fast in the subway line. This is not only inaccurate, but also ridiculous and unnecessary. Volcanic lava can possibly move faster when in a concealed area that insulates it, but insulated lava cannot move that fast.
New today 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.
New today Factual error: During specific scenes, volcanic gas is shown to have vaporized several city workers entirely, burned half a workers' head to the point where it appeared coal black, steamed rats, and vaporized Amy's friend. Volcanic gas in real life could burn a subject, but not instantly vaporize them like it did in the movie.
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.
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.