Some of the melt rises toward the Earth's surface to erupt, forming a chain of volcanoes (the Cascade Volcanic Arc) above the subduction zone. The addition of melted crust changes the geochemical composition. This newly formed magma ascends upward through the crust along a path of least resistance, both by way of fractures and faults as well as by melting wall rocks. The water vapor rises into the pliable mantle above the subducting plate, causing some of the mantle to melt. 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. īeneath the Cascade Volcanic Arc, a dense oceanic plate sinks beneath the North American Plate a process known as subduction. The volcanoes and earthquakes arise from a common source: subduction. The Ring of Fire is also known for its frequent earthquakes. The Cascade volcanoes define the Pacific Northwest section of the Ring of Fire, an array of volcanoes that rim the Pacific Ocean. Rising above this volcanic platform are a few strikingly large volcanoes that dominate the landscape. Helens get the most attention, the Cascade Volcanic Arc includes a band of thousands of very small, short-lived volcanoes that have built a platform of lava and volcanic debris. Volcanoes The Cascade Volcanoes Īlthough the largest volcanoes like Mount St. The Coast Mountains and Insular Mountains are a strip of mountains along the coast of British Columbia, each with its own geological history. The Columbia Plateau is a region of subdued geography that is inland of the Cascade Volcanoes, and the North Cascades are a mountainous region in the northwest corner of the United States, extending into British Columbia. The Cascade Volcanoes are an active volcanic region along the western side of the Pacific Northwest. There are at least five geologic provinces in the area: the Cascade Volcanoes, the Columbia Plateau, the North Cascades, the Coast Mountains, and the Insular Mountains. Since that date, the western edge of North America has grown westward as a succession of island arcs and assorted ocean-floor rocks have been added along the continental margin. Most of the region began forming about 200 million years ago as the North American Plate started to drift westward during the rifting of Pangaea. The geology of the Pacific Northwest is vast and complex. ![]() The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides. ![]() The geology of the Pacific Northwest includes the composition (including rock, minerals, and soils), structure, physical properties and the processes that shape the Pacific Northwest region of North America.
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