Mount Thielsen, Extinct stratovolcano in southern Oregon, United States.
Mount Thielsen is an extinct stratovolcano in the southern Cascade Mountains of Oregon, rising to 9,182 feet (2,799 meters). The sharp spire formed when glaciers carved away the volcanic rock over thousands of years.
Volcanic activity stopped around 250,000 years ago after eruptions deposited layers of basaltic andesite. Glaciers later reshaped the original dome into the needle-like form seen today.
The Klamath people called this peak hisc'akwaleeʔas before settlers renamed it after railroad engineer Hans Thielsen. Hikers today follow trails through the wilderness area that carries the mountain's current name.
Hiking trails wind through 55,100 acres of wilderness around the peak and connect with the Pacific Crest Trail. Most routes require good fitness, especially for the steep summit climb over loose rock.
Lightning strikes hit the summit so often that they create fulgurite, a glass-like mineral formed from melted rock. These lightning tubes sometimes lie scattered across the upper slopes, showing the electrical activity of the area.
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