"Mount Hood's last major eruption occurred in the 1790's not long before Lewis and Clark's expedition to the Pacific Northwest. In the mid-1800's, local residents reported minor explosive activity, but since that time the volcano has been quiet. Someday, however, Mount Hood will erupt again. What will those eruptions be like and how will they affect us? Scientists from the U.S. Geological Survey (USGS) are studying the volcano's past eruptive behavior to better anticipate and prepare for future eruptive activity."
U.S. Geological Survey: http://www.usgs.gov/