Gr 4-6--These useful books, which include information on environmentalism, are divided into chapter spreads that sometimes concentrate on particular examples, such as “Niagara Falls” in Mighty Rivers, and at other times focus more on processes or features, such as “Volcanic Ridge” in World’s Oceans. Chapters are labeled as “Case Study” or “Science Report,” making the presentation lively. The concise explanations include just the right number of examples and clear diagrams, and have perfect color photo accompaniments. “News Flash” sidebars provide details of past disasters and can be fascinating, but they sometimes repeat information that is in the text or the photo captions. Earthquakes provides the most material that is not found elsewhere, such as a discussion of how human activity can trigger earthquakes, and uncommon details on the earthquake that triggered the 2004 Indian Ocean tsunami.