An active volcano on Hawaii; a laboratory simulates a tsunami; tsunami history and damage; whether a tsunami will happen again on the West Coast.

Yellowstone National Park, the site of a potential supervolcano; Meteor Crater, in Arizona; powerful telescopes on Maui search the universe for meteors that might be headed Earth's way.

The Florida Everglades; Yellowstone's ecosystem; Earth as a giant ecosystem; the interdependency of all living things.

Mount Washington, N.H. -- "the home of the world's worst weather"; Florida's "Wall of Wind," where scientists simulate hurricane-force winds; a scientific research team pursues a tornado; destruction of debris thrown by tornadoes.

The Poconos of Pennsylvania; plants that eat insects; edible forest plants; how plants communicate.

Causes of recent forest-fires; lightning strikes; a glacier and an ice cave in Iceland; why glaciers are melting and how it will change the sea level.