Have you visited Hawai'i National Park and gotten close to the Kīlauea Volcano, enjoyed Paradise at Mount Rainier National Park, climbed to the top of Lassen Peak in its namesake park, or hiked down to Crater Lake? If so, you've placed yourself in the midst of some of the country's most dangerous volcanoes in terms of the threats they pose, according to the U.S. Geological Survey.