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  • Country
  • Subregion Name
  • Primary Volcano Type
  • Last Known Eruption
  • 44.674°N
  • 121.8°W

  • 3199 m
    10493 ft

  • 322020
  • Latitude
  • Longitude

  • Summit

  • Volcano

There are no activity reports for Jefferson.

 Available Weekly Reports

There are no Weekly Reports available for Jefferson.

Summary of eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
0950 (?) Unknown Confirmed   Varve Count S of Jefferson (South Cinder Peak)
4500 BCE ± 50 years Unknown Confirmed   Varve Count SSE of Jefferson (Forked Butte)

The following references are the sources used for data regarding this volcano. References are linked directly to our volcano data file. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title. Additional discussion of data sources can be found under Volcano Data Criteria.

Greene R C, 1968. Petrography and petrology of volcanic rocks in the Mount Jefferson area, High Cascade Range, Oregon. U S Geol Surv Bull, 1251-G: 1-48.

Harris S L, 1988. Fire Mountains of the West: the Cascade and Mono Lake Volcanoes. Missoula, MT: Mountain Press, 379 p.

Hildreth W E, 2007. Quaternary magmatism in the Cascades--geologic perpectives. U S Geol Surv Prof Pap, 1744: 1-125.

Scott W E, 1977. Quaternary glaciation and volcanism, Metolius River area, Oregon. Geol Soc Amer Bull, 88: 113-124.

Sherrod D R, Smith J G, 1990. Quaternary extrusion rates of the Cascade Range, northwestern United States and southern British Columbia. J Geophys Res, 95: 19,465-19,474.

Walker G W, Greene R C, Pattee E C, 1966. Mineral resources of the Mount Jefferson primitive area, Oregon. U S Geol Surv Bull, 1230-D: 1-32.

Wood C A, Kienle J (eds), 1990. Volcanoes of North America. Cambridge, England: Cambridge Univ Press, 354 p.

Mount Jefferson, Oregon's second highest peak, is a deeply eroded stratovolcano that has been inactive since the late Pleistocene. The glacier-clad landmark prominent from both sides of the Cascade Range was named by Lewis and Clark for the president that sponsored their expedition. Jefferson was constructed in two episodes interrupted by extensive glacial erosion. The first of these, beginning about 290,000 years ago, produced an andesitic-to-dacitic volcano possibly higher than the current summit. Dacitic lava domes were emplaced during the 2nd cycle beginning about 70,000 years ago that produced ash flows that traveled 15 km to the east and west. Several Holocene cinder cones near the Cascade crest south of Jefferson have produced lava flows that traveled down glacially carved valleys, including those from Forked Butte and North Cinder Peak. The most recent eruption, from a cinder cone on the flank of the South Cinder Peak cone, produced a lava flow that traveled west into Marion Lake about 1000 years ago.