
Mt. Thielsen
Posted by:
Volcanoguy
N 43° 07.524 W 122° 08.452
10T E 569884 N 4775098
Geologic history sign at the Mt. Thielsen Viewpoint on Ore. Hwy. 230.
Waymark Code: WM7QCZ
Location: Oregon, United States
Date Posted: 11/22/2009
Views: 1
Marker Name: Mt. Thielsen - Lightning Rod of the Cascades
Marker Text: The distinctive peak of Mt. Thielsen attracts more than just attention from sightseers; this spire is also a tempting target for lightning, which has actually melted rock on the summit! The spire is the hardened core of the old volcano that built Mt. Thielsen. How did it look as a young mountain?
In the Beginning -- Thielsen formed about 300,000 years ago through a series of volcanic eruptions. The result was probably a cone-shaped peak bearing little resemblance to what we see today. What caused the change?
The Sculptors -- During the ice ages following its formation, the mountain was covered by massive sheets of ice that inched down its sides, grinding away the slopes.
A Hardened Core -- Thousands of years of grinding by ice sculpted the mountain to the general shape we see today. Because the central plug was harder than the surrounding material, it survived.
Historic Topic: Geological
 Group Responsible for placement: Forest Service
 Marker Type: Roadside
 Region: Willamette Valley
 County: Douglas
 State of Oregon Historical Marker "Beaver Board": Not listed
 Web link to additional information: Not listed

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