Mount Rainier, also known as Tahoma, is a large active stratovolcano in the Cascade Range of the Pacific Northwest in the United States. The mountain is located in Mount Rainier National Park about 59 miles (95 km) south-southeast of Seattle. With a summit elevation of 14,411 ft (4,392 m), it is the highest mountain in the U.S. state of Washington, the most topographically prominent mountain in the contiguous United States, and the tallest in the Cascade Volcanic Arc.

A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high to intermediate levels of silica, with lesser amounts of less viscous mafic magma. Extensive felsic lava flows are uncommon, but have traveled as far as 15 km (9 mi).