Matthew McConaughey’s modern-day explorer Dirk Pitt – the priceless name and character come from Clive Cussler’s series of novels – is a riff on Indiana Jones, if Indiana Jones had spent three years in the weight room. McConaughey may be weighty, but Sahara – in which the star, Steve Zahn and Penelope Cruz chase a lost Civil War battleship across West Africa (don’t ask) – is not. The movie takes itself just seriously enough to justify its existence on the screen.