Mount Shasta

Geology and History

Mount Shasta is located in the Cascade Range in northern California about 65 km (40 mi) south of the Oregon-California border. One of the largest and highest (14,162 ft) of the Cascade volcanoes, the compound stratovolcano is located near the southern end of the range that terminates near Lassen Peak.

Mount Shasta's southwest slope with a view facing north-northeast....

Mount Shasta's southwest slope with a view facing north-northeast. (Credit: Doukas, Mike. Public domain.)

Mount Shasta was primarily constructed during four major cone-building episodes that were centered on separate vents. Each of the cone-building periods produced andesite lava flows, block-and-ash flows, and mudflows originating mainly at the central vents. Construction of each cone was followed by more silicice ruptions of domes and pyroclastic flows at central vents, and of domes, cinder cones, and lava flows at vents on the flanks of the cones. Mount Shasta's estimated volume is 350 km3 (84 mi3).

Two of the main eruptive centers at Mount Shasta, Shastina (3,758 m 12,303 ft), and Hotlum cones were constructed during Holocene time, which includes about the last 10,000 years. Holocene eruptions also occurred at Black Butte, a group of overlapping dacite domes about 13 km (8 mi) west of Mount Shasta. The extrusion of the domes about 9,500 years ago was accompanied by the formation of pyroclastic flows, which extended more than 10 km (6.2 mi) south and 5 km (3.1 mi) north of the domes. Evidence of geologically recent eruptions at these two main vents and at flank vents forms the chief basis for assessing the most likely kinds of future eruptive activity and associated potential hazards.

Streams that head on Mount Shasta drain into the Shasta River to the northwest, the Sacramento River to the west and southwest, and the McCloud River to the east, southeast, and south. Mount Shasta hosts five glaciers: Bolam, Hotlum, Konwakiton, Whitney, and Wintun glaciers. Whitney Glacier is the largest glacier in California.

Mount Shasta was designated a National Landmark in December of 1976.