One of the plot elements that crops up in the movie is a volcanic area that the tunnelers run into about halfway across the Atlantic. This makes sense, as the Mid-Atlantic Ridge is a very active area. The neat part in relation to the movie is that while the existence of a "Ridge" on the seafloor was known at the time, it was not known that it was so active. It wasn't until the Heezen/Ewing/Tharp mapping of the ocean floor in the 1950s that people discovered that Seismic activity and "Seafloor Spreading" due to magma seepage were going on. That was about 20 years after the makers of the film surmised Magma pockets near the Mid-Atlantic.