MT. RAINIER

Mount Rainier is part of the Cascade Range, which stretches from British Columbia in Canada through Washington, Oregon, and Northern California. Washington proudly claims Mount Rainier.

     The Cascades are famous for their volcanic peaks, many of which are still considered active or potentially active—Rainier included. Other well-known Cascade volcanoes include Mount St. Helens, Mount Adams, Mount Hood, and Mount Shasta.

     Like the other Cascade volcanoes, Mount Rainier formed due to subduction—a geological process involving tectonic plates in which one tectonic plate slides beneath another.

     In the case of Mt. Rainier and the other Cascades, the Juan de Fuca Plate — a small oceanic plate — is slowly sliding beneath the North American Plate at the Cascadia Subduction Zone, just off the Pacific Northwest Coast. As the Juan de Fuca Plate sinks into Earth's mantle under North America's edge, it releases seawater, lowering the melting point of the overlying mantle and creating magma. The magma rises through the Earth's crust and erupts at the surface. The erupted matter builds up gradually over geologic time, eventually forming large volcanic cones — Mount Rainier is one such cone.

      Mount Rainier has reached its current elevation of 14,411 feet over hundreds of thousands of years, primarily through explosive eruptions and lava flows building layer after layer of ash, pumice, and other volcanic debris.

     Scientists consider Mt. Rainier an active volcano, though no great eruptions have occurred in over 500 years. However, it shows signs of ongoing geothermal activity (like steam vents and hot springs), and scientists monitor it closely. You may recall the 1980 fiery eruption of one of its neighbors, Mount St. Helens, 50 miles away as the crow flies.