World Library  
Flag as Inappropriate
Email this Article
 

Three Fingered Jack

Three Fingered Jack
Southwest side of Three Fingered Jack seen from Pacific Crest Trail.
Elevation 7,844 ft (2,391 m) NAVD 88[1]
Prominence 2,481 ft (756 m)[2]
Location
Location Jefferson and Linn counties, Oregon, U.S.[3]
Range Cascades
Coordinates [1]
Topo map USGS Three Fingered Jack
Geology
Type Shield volcano
Age of rock older than 200,000 years
Volcanic arc Cascade Volcanic Arc
Climbing
First ascent 1923

Three Fingered Jack, named for its distinctive shape, is a Pleistocene volcano in the Cascade Range of Oregon. It is a deeply glaciated shield volcano and consists mainly of basaltic andesite lava.[4] Compared with other heavily glaciated volcanic peaks such as Mount Washington and Mount Thielsen, which display eroded volcanic necks as their cores, Three Fingered Jack's present summit is a narrow ridge of loose tephra supported by a dike only 10 feet (3.0 m) thick on a generally north–south axis. Radiating dikes and plugs from a series of overlapping cinder and composite cones that support this summit have been exposed by glaciation.[5]

The sole glacier is the unofficially-named Jack glacier, located in a shaded cirque on the northeast side at an unusually low altitude for the Oregon Cascades. The last cone-building eruptions were more explosive in nature than earlier shield-building eruptions, producing mostly unconsolidated strata. Cone-building eruptions ceased before the Pleistocene glacial period, allowing the expanded glacial cover to remove most of the cone.[5]

Sources disagree about who first reached the summit; it was either six boys from Bend, Oregon,[6] or members of The Mazamas.[7] Sources agree that the ascent occurred in 1923.

Three Fingered Jack is located in the Mount Jefferson Wilderness and is not accessible by paved road, but can be approached by the Pacific Crest Trail.[8] It is regarded as extinct and has not been assessed for volcanic hazards.[5]

References

  1. ^ a b
  2. ^
  3. ^
  4. ^
  5. ^ a b c Harris, pp. 163–164
  6. ^ Grubbs, p. 68
  7. ^
  8. ^ Harris, p. 165

Works cited


This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.