Maximilian Schell doesn't entirely persuade as “Hansen,” the sea captain setting out for the Dutch East Indies in pursuit of a shipwreck. His motivation comes from "Laura" (Diane Baker), who suggests that a submarine, carrying pearls, lies submerged—a submarine where her deceased husband once served. To assist him, he hires the experienced diver “Connerly” (Brian Keith) and the eager young “Rigby” (John Leyton), equipped with a diving bell, along with "Leoncavallo" (Sal Mineo), who brings his own hot air balloon. Their quest for riches begins. However, there are problems. The agreement to allow them to explore was conditional on bringing along a group of undesirable individuals, and as these men become aware of the true purpose of the expedition, thoughts of rebellion begin to surface. Adding to the tension, their journey takes place beneath the shadow of a volcano displaying troubling signs of an impending eruption. "Hansen" finds himself with numerous challenges, few allies, and ominous clouds of smoke—making success seem unlikely. The actors are all pleasant to look at, but they're burdened with delivering rather uninspired lines and struggle to inject excitement into what’s unfolding through their interpersonal conflicts, romantic entanglements, and resentments. A stronger central figure would have helped, as would a smaller ensemble cast allowing the story to concentrate more on the treasure hunt than individual personalities. The film does manage to improve considerably in its final fifteen minutes when Krakatoa seems to grow tired of watching and makes its displeasure known. A mix of real footage and some rather striking visual effects vividly portray nature’s power and fury as it interrupts a slow-moving drama. It's not an awful movie, but don't anticipate any significant complexity in the narrative or the characters portrayed.

Source on TMDB