Mount Hood Volcano, Oregon: Number 4 of America's Ten Most Dangerous Volcanoes

Climbers cross a ridge on Oregon's most dangerous volcano, Mount Hood. "A key issue with Mount Hood is that people live on the flank of the volcano, state highways cross its flanks—so there's a lot of stuff up close," the Cascade Volcano Observatory's Scott said.

Mount Hood was very active at the end of the last ice age, and there have been two significant eruptions in the last 1,500 years—the last of which happened just before Lewis and Clark came through in the early 1800s.

One interpretation of Mount Hood's volcanic activity is that the mountain has recently ended a long period of dormancy and "in the future it might be erupting on the order of every few centuries," Scott said. - Source