USGS/Cascades Volcano Observatory, Vancouver, Washington
Mount Thielsen Volcano, Oregon
- Mount Thielsen Volcano
- Mount Thielsen Trail
- Mount Theilsen Wilderness
- Hans Thielsen
Aerial view Mount Thielsen, Oregon.
USGS Photograph taken in September 1987, by W.E. Scott.
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Wood and Kienle, 1990, Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.191-192,
Contribution by David R. Sherrod
Mount Thielsen (2,800 meters; 9,187 feet) is a normally polarized
shield volcano comprising approximately 8 cubic kilometers of basaltic andesite built
atop a broad pedestal (24 cubic kilometers) of older lava. Thielsen is remarkable even at
a distance for its colorfully interbedded pyroclastic rocks that dip away from the jagged
spire of the central plug, often called the "lightning rod of the Cascades". The most
spectacular views are on the north and east sides (accessible only by foot or horseback)
where now-vanished glaciers have carved precipitous cirque walls that reveal the
construction. Thielsen's age is approximately 290,000 years (whole-rock K-Ar), and
its geomorphology is a reference point for assigning Cascade Range volcanoes to the age
division 0-0.25 million years (younger than Thielsen) or 0.25-0.73 million years (older
than Thielsen). Very little of Thielsen's underpinnings are exposed because Holocene
which erupted from vents at
Crater Lake National Park
(20 kilometers south), forms a shroud 4-20 meters thick in the Thielsen area.
Mount Thielsen is similar to many of the basaltic andesite shields that form the
bulk of the
High Cascades in Oregon.
It consists of a central pyroclastic cone built of
scoriaceous to pumiceous cindery tuff and coarse breccia. Variations in grain size define
the bedding, which is made more spectacular by the alteration of glassy tephra to colorful
palagonite. The beds mainly dip 10-40 degrees away from the central conduit-filling plug,
although locally these beds have been steepened and even overturned during the plug's
intrusion, a feature unreported from other shields in the Cascade Range. Dikes and sills
lace the cone.
The lava of Mount Thielsen forms stacks of gently dipping flows and breccia as much
as 100 meters thick. Single lava flows are as thin as a few centimeters near their vents
but thicken to more than 10 meters downslope. Fountaining from dike-fed eruptions around
the edge of the cone generated coalescing spatter, which formed many of the flows. In
the eastern cirque wall, lava is preserved draining back toward the dikes. Lava moving
downslope from these satellitic vents probably rafted away parts of the cone. ...
Thielsen's summit spire is a thick sheet of two-pyroxene basaltic andesite 500
meters across at the lowest exposures but dividing upward. The conduit-filling magma
congealed without multiple intrusion.
Thielsen has been glaciated many times since its eruptions around 300,000 years
ago. A talus rampart in the north cirque still protects a very small permanent snowfield
("Oregon's southernmost glacier") shown as Lathrop Glacier on the new 7.5-minute
Mount Thielsen is located near Diamond Lake and north of Crater Lake
National Park, in the Umpqua National Forest. ... Trails from Oregon Highway
138 lead up the south and west sides of Thielsen.
U.S. Forest Service Umpqua National Forest Website, March 2002
Go 1.5 miles north of the Highway 230/Highway 138 road junction near Diamond Lake.
The trailhead parking lot is located along the east side of Highway 138.
A USFS Northwest Forest Pass is required to park at this trailhead.
Umpqua National Forest Recreation Map reference number is L-6.
Located at Township 28 south, Range 5 1/2 east, Section 16.
Attractions and Considerations:
The trail leads through lodgepole pine for the first mile. Timberline is at
approximately 7,200 feet elevation. The mountain hemlock-true fir
type is predominant. Inviting glimpses of Mount Thielsen are evident as one progresses.
A breath taking view of Mount Thielsen presents itself
just beyond the Spruce Ridge Trail junction 1.6 miles.
As you reach the Pacific Crest National Scenic Trail 2.9 miles,
the glacial features of this volcanic peak loom before you. From the Pacific
Crest National Scenic Trail, a scramble trail works its way to the
spire pointed peak at 9,182 feet elevation. The trail is a steep climb,
particularly above timberline beyond which there are no markers.
The last 200 feet is a difficult hand-over-hand climb. Elevation gain is
Hiking boots and caution are highly recommended for
climbing on the loose rocky slopes. Those brave and energetic enough to make it to
the top, should add their names to the climbing
register found there. The view of the east and west sides of the Cascades, from the Sisters
to Mount Shasta, is incredible.
This trail is used in the winter time by Nordic
skiers up to the Pacific Crest National Scenic Trail.
Mount Thielsen Wilderness
From: U.S. Forest Service Winema National Forest Website, 2002
Much of the Mount Thielsen Wilderness is made
up of high alpine forests and open
meadows. Elevations range from 5,000 feet to
the 9,182 summit of Mount Thielsen, the
"lightening rod of the Cascades."
The Pacific Crest National Scenic Trail winds
through the Mount Thielsen Wilderness for 26
miles along the summit of the Cascade Range.
A trailhead on Highway 138, one mile east of
the north entrance to Crater Lake National Park,
is the southern entrance point.
U. S. Forest Service Umpqua National Forest Website, 2002
Mount Thielsen, (Diamond Lake Ranger District; Umpqua National
Also known as Big Cowhorn.
This mountain was known as Hischokwolas to Indians of the area.
This rugged horn-like mountain is unique and very
Lewis A. McArthur, 1982, Oregon Geographic Names: Western Imprints, The
Press of the Oregon Historical Society.
About 1872 it was named Mount Thielsen by John A. Hurlburt of
Portland, in honor of Hans Thielsen, prominent pioneer railroad
engineer and builder.
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05/28/02, Lyn Topinka