A massive earthquake strikes the United States, which destroys the West Coast and unleashes a massive flood that threatens to destroy the East Coast as well.
If you're wondering about this film and why it's dubbed in Italian, then read the following comment from IMDb:
I have always wondered about the disappearance of "Deluge". Why for so many years, seemingly since it's release in 1933, this film vanished from the face of the earth. After seeing it, courtesy of the efforts of Mr. Wade Williams & Co., I'm still puzzled, but I have a theory. In 1933, "the code" was enacted that pretty much took care of sex and violence in Hollywood. While not an explicit film by any means, "Deluge" does deal fairly frankly with sexuality, lust and rape. I wonder if RKO discovered they had a film that they could not re-release, much like the fabled lost Warner Bros. comedy "Convention City". It's a shame for, while it is a dated film, I find it quite unique and surprising for it's era and a fairly successful attempt to create something different in an era when films were already becoming cookie cutter by-products of the studio machine (not that many of those cookies aren't tasty, mind you). And even though the only available copy at this writing is dubbed into Italian, I don't find that a hinderance. An excellent job was done in subtitling the film, and much of the film is visual anyway.