Mount Jefferson

Mount Jefferson is a stratovolcano in the Cascade Volcanic Arc, part of the Cascade Range in the U.S. state of Oregon. The second highest mountain in Oregon, it is situated within Linn County, Jefferson County, and Marion County and forms part of the Mount Jefferson Wilderness. Due to the ruggedness of its surroundings, the mountain is one of the hardest volcanoes to reach in the Cascades. It is also a popular tourist destination despite its remoteness, with recreational activities including hiking, backpacking, mountaineering, and photography. Vegetation at Mount Jefferson is dominated by Douglas fir, silver fir, mountain hemlock, ponderosa pine, lodgepole pine, and several cedar species. Carnivores, insectivores, bats, rodents, deer, birds, and various other species inhabit the area.

Also known as Seekseekqua by Native American populations, the volcano was named after United States President Thomas Jefferson, and was first ascended by E. C. Cross and R. L. Farmer in 1888. It sits atop an area of crustal melting, and was produced by the subduction of the oceanic Juan de Fuca tectonic plate under the continental North American tectonic plate, forming about 730,000 years ago. Consisting of basaltic andesite, andesite, and dacite, the mountain has been extensively altered by glacial erosion. The surrounding area contains a number of other volcanic features like cinder cones, shield volcanoes, and tuyas (flat-topped, steep-sided volcanoes formed when lava erupts through a thick glacier or ice sheet). It is considered a low threat by the United States Geological Survey. Despite the low chance of future eruptions, many scientists still consider mudflows a major threat at Mount Jefferson.