Where the Sierra Nevadas end, a chain of explosive volcanic centers begins, known as the Cascade volcanoes. The Cascades region forms an arc-shaped band extending from British Columbia to northern California, roughly parallel to the Pacific coastline. Within this region, thirteen major volcanic centers lie in sequence like a string of explosive pearls. Although the largest volcanoes, such as Mount St. Helens, get the most attention, the Cascade Range 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.

The Cascades volcanoes define the Pacific Northwest section of the “Ring of Fire,” a fiery array of volcanoes that rim the Pacific Ocean. As if volcanic hazards were not enough, the Ring of Fire is also infamous for its frequent earthquakes. In order to understand the origins of this concentrated band of Earth's hazards, we have to take a peek beneath our feet.

Beneath the Cascades, a dense oceanic plate plunges beneath the North American Plate in a process known as subduction. As the oceanic slab sinks deep into the earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The water vapor rises into the pliable mantle above the sinking plate, causing some of the mantle to melt into magma. This newly formed magma rises toward the earth's surface and erupts, forming a chain of volcanoes (the Cascade Range) above the subduction zone. Are there more eruptions in our future? As long as subduction continues, new Cascade volcanoes will continue to rise.¹