When Anderson drives the Jeep and passes the helicopter, the sun's position changes when the camera angle does, revealing that the shots were filmed at different times of the day.
An oil rig drilling into the side of a volcano triggers the eruption. Oil fields are not found on or near active volcanoes; there is not enough time between eruptions for any petroleum products to form or be deposited.
Gilmore says the victims of the Mt. Pelée eruption suffocated after the explosion sucked oxygen out of the air. The major killer was actually a pyroclastic flow of gas and volcanic debris that buried and incinerated a huge portion of the town of Saint-Pierre.
When the lava bombs hit, they explode. Lava bombs are blobs of semi-melted rock. They may splatter, but they do not explode.
After night falls, the characters and/or the camera view the volcano From various angles, some 90 degrees removed from one another, but the same side of the volcano is visible, with the same patterns of lava flow. It is clearly a piece of stock footage matted into the frame.
When one of Nikki's ranch hands falls from Hank's helicopter, he falls sideways through the air.
The survivors emerge from the cave the next morning to sunny and clear skies and calm seas. Even if they were on the other side of the island, there should be at least residual disturbances in the atmosphere.
The size of the volcano and the distance from the hotel when viewed from the cave is too close.
When Paul Newman and the little girl are knocked loose while crossing the bridge, the harness holding her to his body can be seen.