Krakatoa was actually located west of Java.
Krakatoa was roughly 12 square miles in size and when it erupted in the most cataclysmic explosion in history it caused the death of 36,000 people. It's estimated the explosions released energy a million times greater than that of a hydrogen bomb. The explosions were so powerful that they transformed Krakatoa's highlands, which were over 1,000 feet high into chasms over a 1,000 feet deep. One of the explosions was heard in the Phillipines and Japan over 3,000 miles away. Tsunami waves reached a height of 150 feet and reached South America and their effect were felt in the English Channel.
The producers learned of the geographic error (Krakatoa was west of Java in the Sundra Strait) only after all of the advertising and publicity materials had been prepared. It was deemed too costly to re-do these materials, and possibly delay the release, for the sake of simple geographic accuracy.
After the success of Earthquake (1974) and its Sensurround process, this film was re-released in Europe in the mid 1970's (under the new title "Volcano") with the addition of Sensurround. In some areas this process was advertised as "Feelarama."
During filming, the Cinerama cameras made so much noise that they drowned out the dialogue. All of the dialogue spoken in the film was re-recorded in post-production.