Tsunamis and Other Natural Disasters by Mary Pope Osborne, Natalie Pope Boyce, Pope Natalie Boyce (2007, Paperback)

"Tsunamis and Other Natural Disasters" is part of a whole series of Magic Tree House Research Guides, coauthored by Mary Pope Osborne (the Magic Tree House lady herself). These are nonfiction books on similar subjects to the corresponding Magic Tree House fiction chapter books, written at a similar or slightly higher reading level (the fiction books tend to be low-high Gr. 2 reading level; these nonfiction Research Guides are generally high Gr. 2-mid Gr. 3 reading level). The interest level on the Magic Tree House Research Guides can stretch to much older children, however; my Gr. 6 daughter's social studies class used the Research Guide tied to the "Hour of the Olympics" chapter book as a textbook for their unit on ancient Greece, and my special-needs 15-year-old son has used several of the Research Guides for reading practice.
Your kids used the Magic Tree House chapter books as they learned to read; now they can use the Magic Tree House Research Guides as they read to learn!