This is only a free book in the sense I got it out of the library. Krakatoa: The Day the World Exploded is, of course, about the Krakatoa explosion in 1883. It's a wonderful book, just my style. It talks about the science of plate tectonics and geophysics that makes volcanoes. It talks about the science history, of how plate tectonics went from a crackpot theory to totally accepted. It talks about the history of Java as a Dutch colony. After the explosion, we get some biology: how does life reappear on an island that got blown up, or in the case of "Son of Krakatoa", on a 100% new volcanic island? And some connection with modern society: how the volcano was a trigger for some radical Islamism. (Odd story there: indigenous Javanese religion treated the volcanoes as gods. That's obviously not Islamic — but nonetheless the eruption was interpreted as an intensely spiritual occurrence).
Anyways, excellent book, and lots of interesting material.
(Oh, and if any pseudoscientists complain that science is insular and rejects crackpot theories, plate tectonics is a wonderful example of how outsiders can get their theories accepted. Hint: have tons of evidence and testable hypotheses.)