Mount St. Helens is classified as a composite volcano, also known as a stratovolcano. This type of volcano is characterized by steep-sided, often symmetrical cones built up by alternating layers of lava flows, ash, and other volcanic debris. Stratovolcanoes like Mount St. Helens tend to erupt explosively and pose significant hazards to nearby areas

. Specifically, Mount St. Helens is part of the Cascade Volcanic Arc in the Pacific Northwest of the United States and has a composition ranging from basalt to rhyodacite

. Its eruptions include explosive events and dome-building phases, typical of stratovolcano behavior

. In summary, Mount St. Helens is a stratovolcano (composite volcano) known for its explosive eruptions and layered volcanic structure.