From an author's point of view, Volcano tries to get students thinking about geology from an applied standpoint. Students are likely to remember, enjoy, and find useful information gained in service of a goal that would be relevant to them. Though most students aren't going to go on to be volcanologists, the danger, excitement, and responsibility of someone in a volcanologist's role in such a crisis is a built-in motivator.
So, what are the pieces of Volcano Investigator, and why are they there?