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Mount Thielsen, or Big Cowhorn, is an extinct shield volcano in the Oregon High Cascades, near Mount Bailey. Because eruptive activity ceased 250,000 years ago, glaciers have heavily eroded the volcano's structure, creating precipitous slopes and a horn-like peak. The spire-like shape of Thielsen attracts lightning strikes and creates fulgurite, an unusual mineral. The prominent horn forms a centerpiece for the Mount Thielsen Wilderness, a reserve for recreational activities such as skiing and hiking. Thielsen was produced by subduction of the Juan de Fuca Plate under the North American Plate. Volcanism near the Cascades dates back to 55 million years ago (mya), and extends from British Columbia to California. Thielsen is part of the High Cascades, a branch of the main Cascades range that includes Oregonian volcanoes less than 3.5 million years old; it is also a member of a group of extinct volcanoes distinguished by their sharp peaks. The area surrounding the volcano was originally inhabited by Chinook Native Americans, and was later encountered by Polish settlers. One of the visitors was Jon Hurlburt, an early explorer of the area who named the volcano after the engineer Hans Thielsen. Later explorers discovered nearby Crater Lake. The volcano was not analyzed until 1884, when a team from the United States Geological Survey sampled its fulgurite deposits. == History == The area was originally inhabited by Chinook Native Americans, who referred to the mountain as "Hischokwolas"; the Klamath call it "hisc'akwaleeas". Jon Hurlburt, a Polish explorer, renamed the volcano after Hans Thielsen, a railroad engineer and builder who played a major role in the construction of the California and Oregon Railroad.〔Heer and Heer, p. 47.〕 In 1884 a United States Geological Survey team headed by J. S. Diller began studying the mountains of the Cascade Range. Their intended destinations included Thielsen, which was climbed and sampled for its fulgurite variant. Thielsen's spire-like top is hit by lightning so frequently that some rocks on the summit have melted into a rare mineraloid known as lechatelierite, a variety of fulgurite. The mountain has earned the nickname "the lightning rod of the Cascades".〔 Apart from study, Thielsen and the rest of the Crater Lake area features heavily into 19th- and early 20th-century exploration. In 1853, miners from Yreka first described Crater Lake; one called it "the bluest water he had ever seen", another "Deep Blue Lake." The first published description was written by Chauncy Nye for the ''Jacksonville Sentinel'' in 1862. Nye recalled an expedition of gold prospectors where they passed a lake of a deep blue color. Native Americans lived in the area and grew irritable towards new settlers in the area. In 1865, Fort Klamath was built as a protective sanctuary. A wagon road was built to connect the Rogue Valley to the building. In late 1865, two hunters ventured upon the lake; more explorers followed. By then, the lake became famous for its distinctive color, and crowds flocked to see it. The first non-Native American to stand on the shore of Crater Lake was Sergeant Orsen Stearns, who climbed down into the caldera. A friend, Captain F.B. Sprague, gave it the name "Lake Majesty." Tourism continued until May 22, 1902; on that day, Theodore Roosevelt designated the lake and surrounding area a national park. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mount Thielsen」の詳細全文を読む スポンサード リンク
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