Mount Thielsen

Mount Thielsen
Mount Thielsen from the air
height	2799  m
location	Oregon , USA
Mountains	Cascade chain
Coordinates	43 ° 9 '10 "  N , 122 ° 3' 59"  W Coordinates: 43 ° 9 '10 "  N , 122 ° 3' 59"  W
Type	Shield volcano
First ascent	1883 by EE Hayden

Mount Thielsen is a shield volcano in southern Oregon , USA . Heavy glacial erosion destroyed the original crater and formed a pyramid-like summit. Because the last of the cone-forming eruptions took place long before the last Ice Age , the shape was preserved.

The summit of Mount Thielsen is often struck by lightning , causing rock formations near the summit to melt, creating lechatelierite or fulgurite . Hence the volcano is nicknamed The Lightning Rod of the Cascade Range .

Surname

The mountain was called Hishokwolas by the natives of the area . He is also known as the Big Cowhorn ( big cow horn ) known. The volcano was named according to the Oregon Geographic Names by Lewis A. McArthur, published in 1982 by the Oregon Historical Society Press , around 1872 by John A. Hurlburt of Portland after Hans Thielsen, a noted railroad engineer and pioneer.

geography

In the vicinity of the 2799 m high shield volcano are the similarly formed Howlock Mountain and the younger Mount Bailey . The latter rises west of Thielsen on the other side of Diamond Lake . Crater Lake National Park begins only about nine kilometers south . Mount Thielsen is on the border between Douglas Counties in the west and Klamath in the east. Similarly, the share national forests (English singing .: National Forest ) Umpqua and Winema the mountain.

geology

The mountain is one of the oldest volcanoes in the Cascade Range. The period of the volcanic cone-forming eruptions of Mount Thielsen was relatively short. Glaciers eroded the summit area in such a way that the volcano no longer has an eruption crater. The current shape was created during the last two or three ice ages.

construction

View over Diamond Lake, 1580 m above sea level, to Mount Thielsen

The volcanic cone of Mount Thielsen was formed on older shield volcanoes and has a volume of 8.3 km³. It consists of breccia , tuff and basaltic andesite , a volcanic rock that occurs frequently in the Cascade Range. The summit area of ​​the volcano is characterized by glacial erosion during the ice ages. The ice masses deformed the cone, exposing parts of the volcanic interior. The K-Ar dating yielded an age of 290,000 years for Mount Thielsen. The last eruptions occurred 100,000 to 250,000 years ago, which means that the volcano's period of activity was quite short. The eruptions occurred in three different periods of time: a period of the cone-forming lava flow, another with more frequent eruptions and a final period in which the cone mainly increased in diameter and extensive deposits formed.

The solidified lava flows on the slopes of Mount Thielsen are between 30 cm and 10 m thick. The volcano has columnar formations of breccia and traces of palagonite . In the basalt of Mount Thielsen were pyroxene , hypersthene and feldspar proven.

glacier

Pleistocene glaciers eroded the caldera . The volcano was glaciated until after the end of the Little Ice Age . In the early 20th century there was still a large amount of ice on Mount Thielsen. The small Lathrop Glacier in the northern Kar is the only glacier today.

Fulgurite

Fulgurite was found only in the summit area, a maximum of 3 m below the highest point . The material is created by lightning strikes in rocks. The fulgurite forms on Mount Thielsen have a diameter of a few centimeters and a length of up to 30 cm. Lightning strikes regularly in the summit area of ​​the volcano and ensures the formation of fulgurite, which has very dark brownish to olive green colors.

Web links

• University of Oregon
• US Geological Survey
• Mount Thielsen on Peakbagger.com (English)

Individual evidence

1. ↑ ^{a b} Description: Mount Thielsen Volcano, Oregon , USGS , accessed April 29, 2011
2. ↑ Mount Thielsen , Skimountaineer.com, April 29, 2011
3. ^ ^{A b c d} Stephen L. Harris: Fire Mountains of the West: The Cascade and Mono Lake Volcanoes , Missoula: Mountain Press Publishing Company, 1988, ISBN 0-87842-220-X
4. ^ Frank Wigglesworth Clarke: Analysis of rocks and minerals from the laboratory of the United States Geological survey, 1880 to 1908 , USGS, 1910
5. ^ O'Connor; Hardison III, Costa: Debris Flows from Failures of Neoglacial-Age Moraine Dams in the Three Sisters and Mount Jefferson Wilderness Areas, Oregon: USGS Professional Paper 1606 , USGS, 2001