Today marks the thirtieth anniversary of the eruption of Mount St. Helens. I was reminded of this by Amanda Dykes who shared a link to these satellite images of Mount St. Helens the images chronicle the years 1979 through 2009. You can view the images individually or open them as a slideshow in Google Earth. All of the images are provided by NASA.
CNN has a narrated slideshow in which eyewitnesses and experts discuss the eruption of Mount St. Helens.
National Geographic has three easily accessible resources about the eruption of Mount St. Helens. Lost On Mount St. Helens is a short video about Ralph Killian who lost his son and daughter-in-law in the eruption of Mount St. Helens and spent a year looking for them. Mountain Transformed is a picture gallery chronicling Mount St. Helens from eruption to today. Rebirth of the Blast Zone is an interactive illustration of the life that exists in the 230 square mile blast zone around Mount St. Helens.
The BBC's Bitesize section has an online lesson about volcanoes that includes Mount St. Helens. The lesson is appropriate for elementary school and middle school students.
And take a trip in the time machine and watch a 1980 CBS News report about the eruption of Mount St. Helens.
For some resources and lessons about volcanoes in general see 5 Resources for Learning About Volcanoes.