Pacific Mountain System - Cascades volcanic province

Where the Sierra Nevada ends a chain of explosive volcanic centers, the Cascade volcanoes, begins. The Cascades Province forms an arc-shaped band extending from British Columbia to Northern California, roughly parallel to the Pacific coastline. Within this region, 13 major volcanic centers lie in sequence like a string of explosive pearls.
Although the largest volcanoes like Mount St. Helens get the most attention, the Cascades is really made up of a band of thousands of very small, short-lived volcanoes that have built a platform of lava and volcanic debris. Rising above this volcanic platform are a few strikingly large volcanoes that dominate the landscape.

Mount St. Helens, shown above, and at least six other volcanoes in the Cascade Range have erupted at least once during historical time. Most of the Cascade volcanic areas contain fumaroles, hot springs, or other evidence of subsurface volcanic heat, but only Mount St. Helens and Lassen Peak have erupted within the past century. USGS photo.	Location map of Cascades volcanoes and volcanic platform. Major volcanic centers are Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, Mount Adams, Mount Hood, Mount Jefferson, Three Sisters, Newberry Caldera, Crater Lake (Mount Mazama), Medicine Lake, Mount Shasta, and Lassen Peak. Click to enlarge.

What is the source of all this volcanic fire power? Why is it concentrated along the continent's edge? Like many questions in geology, the answers begin with the story of plate tectonics. . .

Continue into the heart of the Cascade volcanoes