The characters and the plot are completely fictional, but the central event, the volcano on Krakatoa erupting, is true. It erupted completely, beginning on August 26, 1883, killing over 30,000 people, an event that shook the world, since it was supposed to have made the loudest noise ever heard in history up to that point, and also because, since the telegraph had already been invented, news of the explosion was able to travel quickly to the rest of the world. There is evidence that this was not the first eruption of the volcano on Krakatoa, though, it apparently having happened several times before. The island, at the time of the explosion, was settled by the Dutch, and of course, in the story, the families are all from the United States. It would be nice to imagine that there were diamonds on Krakatoa, but I'm not aware of any evidence to show that this was likely, or even possible.