Mount St. Helens National Monument, Washington

Kaboom! In 1980, nearly 4 billion cubic yards of mountaintop blasted skyward in an instant. Nearly 230 square miles of forest blown down or buried beneath volcanic ash and mud.

Even now, decades after an eruption that impacted nearly all of the Pacific Northwest, Mount St. Helens is ranked as the most famously unstable mountain in North America.

The geology here is fascinating, of course, but so is the quieter spectacle of forests and meadows gradually reclaiming the mountain’s scorched slopes. Must-sees include Johnston Ridge Observatory and Blowdown Forest and Spirit Lake Viewpoints. More