When McLaughlin and Dr. Foxley sneak down into the tunnel to the spot where "Frank got it", the cooling lines which previously broke are missing from the walls.
Jose is shown wearing what looks like a straw hat while underground. Sandhogs and other underground workers in New York are required to wear hard hats at all times when underground.
The flying manhole cover would have certainly smashed the birdbath to bits upon contact, not just knock it over.
A man opens the door of the house and lava, which is obviously well over five feet deep, flows. This is impossible, as, given the temperature of lava, the wood framed house would have caught fire as soon as the first bit of lava touched it.