Mount Thielsen
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| Mount Thielsen | |
|---|---|
 Mount Thielsen from Diamond Lake |
|
| Elevation | 9,182 feet (2,799 m)[1] |
| Location | Douglas, Oregon, USA |
| Range | Cascades |
| Prominence | 3,342 feet (1,019 m)[2] |
| Coordinates | [3] |
| Topo map | USGS Mount Thielsen 43122-B1 |
| Type | Stratovolcano |
| Volcanic arc/belt | Cascade Volcanic Arc |
| Age of rock | about 290,000 years |
| First ascent | 1883 by E. E. Hayden |
| Easiest route | scramble |
Mount Thielsen is an extinct stratovolcano in southern Oregon that has been so deeply eroded by glaciers that there is no summit crater and the upper part of the mountain is more or less a horn. The reason for this is twofold; Thielsen is a relatively old Cascade volcano and it stopped cone-building eruptions relatively early. It therefore was not able to repair damage caused during the last two or three ice ages.
Thielsen's spire-like top is hit by lightning so often that some of its summit rocks have melted into a rare mineraloid called lechatelierite a variety of fulgurite, and the mountain itself has earned the nickname "the lightning rod of the Cascades."[4][5]
Diamond Lake lies to the west of Mount Thielsen; beyond that lies Mount Bailey, a much less eroded and younger stratovolcano.
Mount Thielsen lies directly north of Crater Lake, and its sharp peak is a prominent feature of the skyline visible from Crater Lake National Park.
[edit] Geology
Mount Thielsen is composed of a shield volcano with a composite cone on top.
The rock formations on Thielsen have normal magnetic polarity, meaning they all likely erupted within the last 700,000 years (it is possible, yet unlikely, that some of the earliest lavas flowed during a previous period of normal polarity).
Thielsen's initial cone was made of pyroclastic material and probably reached a height of about 1,000 to 3,000 feet (~300-900 meters). Around this cone there were peripheral eruptions of basaltic-andesite, which deposited scoria, cinders, and thin flows of lava. Thielsen's construction was later completed when a half mile (800 m) wide plug of basaltic andesite was emplaced in the volcano's main vent. Since then numerous glaciers have eroded most of the mountain's volume.
[edit] See also
[edit] References
- ^ NGS Data Sheet for MT THIELSEN. U.S. National Geodetic Survey. Retrieved on 2008-04-02.
- ^ Mount Thielsen, Oregon. Peakbagger.com. Retrieved on 2008-04-02.
- ^ USGS GNIS: Mount Thielsen. Retrieved on 2008-04-02.
- ^ Purdom, William B. (1966). "Fulgurites from Mount Thielsen, Oregon". The Ore-Bin Vol. 28 (No. 9). Oregon Department of Geology and Mineral Industries.
- ^ Cascade Range Volcanoes Summaries. USGS Cascades Volcao Observatory. Retrieved on 2008-04-01.
- Harris, Stephen L. (1988). Fire Mountains of the West: The Cascade and Mono Lake Volcanoes. Missoula: Mountain Press Publishing Company. ISBN 0-87842-220-X.
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