Mount Jefferson
Elevation:	10,497 ft (3,199 m)
Location:	Oregon, USA
Range:	Cascades
Coordinates:	44°40′27.48″N, 121°47′58.46″W
Topo map:	USGS Mount Jefferson
Type:	Stratovolcano
Age of rock:	< 100 Kyr
Last eruption:
First ascent:	1888 by R. L. Farmer and E. C. Cross
Easiest route:	rock climb

For other mountains named Mount Jefferson, see Mount Jefferson

Mount Jefferson is a possibly extinct stratovolcano in the Cascade Range and is the second-highest mountain in Oregon. Jefferson is in a rugged wilderness and is thus one of the hardest volcanoes to reach in the Cascades (logging road 1044 does come within 4 miles (6 km) of the summit, however). Many people consider Jefferson's craggy, deeply glacially-scarred appearance to be especially beautiful and photogenic. The peak has therefore frequently served as a backdrop for automobile and alcohol advertisements in the United States. USGS photo of Mount Jefferson Source URL: http://vulcan. ... A topographical summit is a point on a surface which is higher in elevation than all points immediately adjacent to it. ... Official language(s) None Capital Salem Largest city Portland Area  - Total  - Width  - Length  - % water  - Latitude  - Longitude Ranked 9th 255,026 km² 420 km 580 km 2. ... The most general definition of a mountain range is a group of mountains bordered by lowlands. ... Mount Adams in Washington The Cascade Range is a mountainous region famous for its chain of tall volcanoes called the High Cascades that run north-south along the west coast of North America from British Columbia to the Shasta Cascade area of northern California. ... Map of Earth showing lines of latitude (horizontally) and longitude (vertically); large version (pdf) The geographic (earth-mapping) coordinate system expresses every horizontal position on Earth by two of the three coordinates of a spherical coordinate system which is aligned with the spin axis of the Earth. ... Example of a topographic map with contour lines Topographic maps, also called contour maps, topo maps or topo quads (for quadrangles), are maps that show topography, or land contours, by means of contour lines. ... The United States Geological Survey (USGS) is a scientific agency of the United States government. ... Mountains can be characterized in several ways. ... A stratovolcano, is a tall, conical mountain (volcano) composed of both hardened lava and volcanic ash. ... The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ... Eruption redirects here. ... In climbing, a first ascent (FA) is the first climb to reach the top of a mountain, or the first to follow a particular climbing route. ... 1888 is a leap year starting on Sunday (click on link for calendar). ... Southern and northern Mount Everest climbing routes as seen from the International Space Station. ... Mount Jefferson can refer to: This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... A stratovolcano, is a tall, conical mountain (volcano) composed of both hardened lava and volcanic ash. ... Mount Adams in Washington The Cascade Range is a mountainous region famous for its chain of tall volcanoes called the High Cascades that run north-south along the west coast of North America from British Columbia to the Shasta Cascade area of northern California. ... Mount McKinley in Alaska has one of the largest visible base-to-summit elevation differences anywhere A mountain is a landform that extends above the surrounding terrain in a limited area. ... Official language(s) None Capital Salem Largest city Portland Area  - Total  - Width  - Length  - % water  - Latitude  - Longitude Ranked 9th 255,026 km² 420 km 580 km 2. ... Bob Marshall Wilderness, Montana, United States Wilderness is land that has not been significantly modified by direct or indirect human activity. ... Eruption redirects here. ... The Abbey Craig, a crag with tail near The University of Stirling. ... Aletsch glacier, Switzerland A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. ... A small variety of cars, the most popular kind of automobile. ... Ethanol, also known as ethyl alcohol or grain alcohol, is a flammable, colorless chemical compound, one of the alcohols that is most often found in alcoholic beverages. ... Generally speaking, advertising is the promotion of goods, services, companies and ideas, usually by an identified sponsor. ...

History

Mt. Jefferson was named in honor of US President Thomas Jefferson by the Lewis and Clark Expedition (this was the only High Cascade mountain they named). The expedition, who were sponsored by President Jefferson, first saw the peak from the mouth of the Williamette River in March 1806. Thomas Jefferson (April 13, 1743 N.S. – July 4, 1826) was the third President of the United States (1801–1809), author of the Declaration of Independence (1776), and one of the most influential Founders of the United States. ... Lewis and Clark The Lewis and Clark expedition (1804–1806) was the first United States overland expedition to the Pacific coast and back, led by Captain Meriwether Lewis and Second Lieutenant William Clark, of the US Army. ... The Willamette River (pronounced wil-LAM-met) is a tributary of the Columbia, approximately 240 mi (386 km) long, in northwestern Oregon in the United States. ... 1806 was a common year starting on Wednesday (see link for calendar). ...

One of the most complete studies of the volcano was complied in a large report written in the 1920s by former professor of geology at the University of Oregon, Edwin T. Hodge. Since then there has been little work done on a comprehensive study of the mountain itself (probably due to its remoteness). The most notable exception was a 1974 study of the volcano's glacial and volcanic history carried out by Kenneth G. Sutton. Referred to as the Jazz Age or primarily in North America and in Australia as the Roaring Twenties . In Europe it is sometimes refered to as the Golden Twenties. ... Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. ... University of Oregon The University of Oregon (UO) is a public university located in Eugene. ... 1974 (MCMLXXIV) is a common year starting on Tuesday (click on link for calendar). ... Aletsch glacier, Switzerland A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. ...

Geology and geography

The average elevation of the terrain around Jefferson is 5,500 to 6,500 ft. (1,600 to 2000 m), meaning that Jefferson's cone still towers nearly a mile above it. Previous studies estimated that the cone is made of roughly equal amounts of tephra and lava, but Sutton's 1974 study found half as much tephra as expected. The remainder of the material thought to be tephra was in fact broken lava rock. Tephra, as a generic term, refers to air-fall material produced by a volcanic eruption - regardless of composition or fragment size. ... Look up lava, Aa, and pahoehoe in Wiktionary, the free dictionary. ...

Sometime before the last magnetic reversal of the Earth's magnetic field 700,000 years ago, the Minto Lavas of 23.4 mile³ (100 km³) total volume created a large volcanic plateau formed from coalescing shield volcanoes that were heavily eroded by glaciers before Jefferson started to grow. The Earths Magnetic Field reverses at intervals, ranging from tens of thousands to many millions of years, with an average interval of ~250,000 years. ... Earth is the third planet from the Sun. ... Current flowing through a wire produces a magnetic field (M) around the wire. ... Mauna Kea, a shield volcano, on the Island of Hawai‘i with a light dusting of snow. ...

Mt. Jefferson started life as a highly explosive vent, which in turn built a tephra-rich cone (this same cone now forms the volcano's core). Much of this structure was subsequently buried under about 5 mile³ (20 km³) of basaltic andesite lava flows that are called the Main Cone Lavas. These lavas form a mass of rock 5 to 40 ft. (1.5 to 12 m) thick near the top of the old cone and become progressively thicker further down the mountain. Basalt Basalt is a common gray to black volcanic rock. ... A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... Sedimentary, volcanic, plutonic, metamorphic rock types of North America. ...

The lack of lahar (volcanic mudflow) or avalanche deposits associated with the original cone and the Main Cone Lavas indicates these these volcanic eruptions probably occurred in a warm interglacial period. Glaciers did directly form on the Main Cone Lavas and did cause erosion later, however. A lahar is a mixture of rock, mud, water and usually debris that flows down from a volcano (or occasionally other mountains), typically along a river valley. ... This article is about volcanoes in geology. ... A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ...

The volcano then went dormant for an unknown period of time, after which somewhat less than 1 mile³ (4 km³) of andesitic lava flows erupted, forming a second stage cone on top of the original (these flows were thicker and had a higher silica content than the Main Cone Lavas). At the same time, two large cone complexes formed on Jefferson's flanks. The North Complex formed near where Jefferson Park now lies and another complex erupted two miles (3 km) south of the mountain's current summit (forming the reddish-brown dacite now seen at Goat's Peak). In addition, more silica-rich andesite lava flowed from fissures of the volcano's south flank. The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ...

A long period of dormancy returned to Jefferson. During that time a succession of large glaciers removed most of the second stage lava along with at least a third of the original cone. Erosion was more severe on Jefferson's western flank and as a result solidified lava flows on the volcano's eastern slope now compose the summit. Jefferson's height before this intense period of glacial erosion is estimated at 12,000 ft (3,700 m). Smaller versions of the ice age glaciers continue to erode Jefferson. Two of the largest, Whitewater Glacier east of the saddle-like part of the summit ridge and Milk Creek Glacier on the west side, threaten to collapse the low ridge that separates them.

Sometime between 40,000 and 140,000 years ago during a glacial maximum, Jefferson changed its behavior from quiet eruptions of lava to violent explosions of pumice-rich tephra and pyroclastic flows. No evidence for later eruptions from the volcano itself has been found, leading researchers to speculate that Jefferson may be extinct. However, it should be noted that Jefferson has awoke from very long periods of inactivity at least twice before. Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Tephra, as a generic term, refers to air-fall material produced by a volcanic eruption - regardless of composition or fragment size. ... Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ...

There have been, however, eruptions in the Jefferson area since Jefferson last erupted.

Reference

• Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, Stephen L. Harris, (Mountain Press Publishing Company, Missoula; 1988) ISBN 0-87842-220-X

External links

• Maps and aerial photos
  • Topographic map from TopoZone
  • Aerial image from TerraServer-USA
  • Surrounding area map from Google Maps
  • Location in the United States from the Census Bureau