Cascade Volcanic Arc
The Cascade Volcanic Arc (also known as the Cascade Volcanoes or the Cascade Arc) is a major range of volcanoes in southwestern British Columbia, Washington, Oregon and in northern California. The arc is central to the Cascade Range, a mountain range in the Pacific Northwest.
It includes about 20 major volcanoes, among a total of over 4,000 separate volcanic vents.
Twelve volcanoes in the arc are over 10,000 ft (3,000 m) in elevation, and the two highest, Mount Rainier and Mount Shasta, exceed 14,000 ft (4,300 m). By volume, the two largest Cascade volcanoes are the broad shields of Medicine Lake Volcano and Newberry Volcano, which are about 145 mi³ (600 km³) and 108 mi³ (450 km³) respectively. Mount Garibaldi and Glacier Peak are the only two Cascade volcanoes that are made exclusively of dacite.
The volcanism in the arc began about 37 million years ago, however, most of the present-day Cascade volcanoes are less than 2,000,000 years old. The most recent major catastrophic eruption in the arc was at Mount St. Helens on May 18, 1980.
The major volcanoes within the arc include Mount Silverthrone, Mount Meager, Mount Cayley, Mount Garibaldi, Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, Mount Adams, Mount Hood, Mount Jefferson, Three Sisters, Broken Top, Mount Bachelor, Newberry Volcano, Mount Thielsen, Mount Mazama (Crater Lake), Mount McLoughlin, Medicine Lake Volcano, Mount Shasta, Shastina,Mount Tehama and Lassen Peak.