Cascade Volcanoes

The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 mi (1,100 km). The arc has formed due to subduction along the Cascadia subduction zone. Although taking its name from the Cascade Range, this term is a geologic grouping rather than a geographic one, and the Cascade Volcanoes extend north into the Coast Mountains, past the Fraser River which is the northward limit of the Cascade Range proper.

Some of the major cities along the length of the arc include Portland, Seattle, and Vancouver, and the population in the region exceeds 10,000,000. All could be potentially affected by volcanic activity and great subduction-zone earthquakes along the arc. Because the population of the Pacific Northwest is rapidly increasing, the Cascade volcanoes are some of the most dangerous, due to their past eruptive history, potential eruptions and because they are underlain by weak, hydrothermally altered volcanic rocks that are susceptible to failure. Mount Rainier is one of the Decade Volcanoes due to the danger it poses to Seattle and Tacoma. Many large, long-runout landslides originating on Cascade volcanoes have inundated valleys tens of kilometers from their sources, and some of the inundated areas now support large populations.

The Cascade Volcanoes are part of the Pacific Ring of Fire, the ring of volcanoes and associated mountains around the Pacific Ocean. All of the known historic eruptions in the contiguous United States have been from the Cascade Volcanoes. Two most recent were Lassen Peak in 1914 to 1921 and a major eruption of Mount St. Helens in 1980. It is also the site of Canada's most recent major eruption about 2,350 years ago at the Mount Meager volcanic complex.