Mont Shasta
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Mont Shasta
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 Vista del mont Shasta prèp de la vila de Weed.
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| Geografia | ||
| Altitud | 4 322 m[1] | |
| Massís | Cadena de las Cascadas | |
| Coordenadas geo. | 41° 24′ 33″ N, 122° 11′ 42″ O | |
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| Administracion | ||
| País |  Estats Units
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| Estat |  Califòrnia
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| Comtat |  Siskiyou
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| Ascension | ||
| Primièra ascension | ||
| Via pus aisida | ||
| Geologia | ||
| Edat | ~593 000 ans | |
| Ròcas | andesita, andesita basaltica, dacita e basalt. | |
| Tipe | estratovolcan | |
| Activitat | Actiu | |
| Darrièra erupcion | 1786[2] | |
| Còde [1] | 323010 | |
| Observatòri volcanologic | Observatòri volcanologic de Califòrnia | |
Lo Mont Shasta (karuk: Úytaahkoo o "mont blanc")[3] (4 317 m) es un volcan actiu situat dins l'Arc volcanic de las Cascadas al nòrd de l'estat de Califòrnia e al nòrd-oèst dels Estats Units d'America. Sa darriera erupcion coneguda se debanèt en 1786.
Es la segonda pus nauta montanha de las Cascadas (aprèp Rainier dins l'estat de Washington). Lo mont forma part dels cinc pics pus nauts de l'Estat de Califòrnia, e tanben dels "Fourteeners" de l'estat.
Geologia modificar
I a environ 593 000 ans, de lavas andesiticas esclatèron dins l'actual flanc oèst del mont Shasta, prèp de la Font de McBride. Al fial del temps, un estratovolcan ancestral del mont Shasta foguèt bastit a una nautor importanta mas desconeguda; i a entre 300 000 e 360 000 ans, tot lo costat nòrd del volcan s'es afondrat, en un enòrme esboldrament e una avalanca de brisum de 27 km³. L'esboldrament s'escolèt cap al nòrd-oèst dins la Val de Shasta, on ara la riu Shasta raja sus 45 km de long.
Çò que rèsta del pus ancian de quatre còns del mont Shasta es expausat a la cresta de Sargent (anglés: Sargents Ridge), al sud de la montanha. Las lavas del vent de la cresta de Sargent cobrisson lo bloquièr d'Everitt Hill al pè sud del mont Shasta. Las darrièras lavas a sortir del vent èran d'andesitas hornblenda-pyroxèn amb un dòma hornblenda en dacita a sa cima. L'erosion glaciària cambièt dempuèi sa fòrma.
Lo còn seguent a formar es expausat al sud de la cima actuala del mont Shasta e s'apèla Misery Hill (literalament Puèg de la Misèria) en anglés. Foguèt format i a 15 000 a 20 000 ans a partir d'escorregudas de'andesita de piroxèn e foguèt dempuèi envasit per un dòma en hornblenda.
What remains of the oldest of Mount Shasta's four cones is exposed at Sargents Ridge on the south side of the mountain. Lavas from the Sargents Ridge vent cover the Everitt Hill shield at Mount Shasta's southern foot. The last lavas to erupt from the vent were hornblende-pyroxene andesites with a hornblende dacite dome at its summit. Glacial erosion has since modified its shape.Modèl:Citation needed
The next cone to form is exposed south of Mount Shasta's current summit and is called Misery Hill. It was formed 15,000 to 20,000 years ago from pyroxene andesite flows and has since been intruded by a hornblende dacite dome.Modèl:Citation needed
There are many buried glacial scars on the mountain which were created in recent glacial periods ("ice ages") of the present Wisconsinian glaciation. Most have since been filled in with andesite lava, pyroclastic flows, and talus from lava domes. Shastina, by comparison, has a fully intact summit crater indicating Shastina developed after the last ice age. Shastina has been built by mostly pyroxene andesite lava flows. Some 9,500 years ago, these flows reached about 6.8 mi (10.9 km) south and 3 mi (4.8 km) north of the area now occupied by nearby Black Butte. The last eruptions formed Shastina's present summit about a hundred years later. But before that, Shastina, along with the then forming Black Butte dacite plug dome complex to the west, created numerous pyroclastic flows that covered 43 sq mi (110 km2), including large parts of what is now Mount Shasta, California and Weed, California. Diller Canyon (400 ft (120 m) deep and 0.25 mi (400 m) wide) is an avalanche chute that was probably carved into Shastina's western face by these flows.Modèl:Citation needed
The last to form, and the highest cone, the Hotlum Cone, formed about 8,000 years ago. It is named after the Hotlum glacier on its northern face; its longest lava flow, the 500-foot-thick (150-metre) Military Pass flow, extends 5.5 mi (8.9 km) down its northeast face. Since the creation of the Hotlum Cone, a dacite dome intruded the cone and now forms the summit. The rock at the 600-foot-wide (180-metre) summit crater has been extensively hydrothermally altered by sulfurous hot springs and fumaroles there (only a few examples still remain).Modèl:Citation needed
In the last 8,000 years, the Hotlum Cone has erupted at least eight or nine times. About 200 years ago the last significant Mount Shasta eruption came from this cone and created a pyroclastic flow, a hot lahar (mudflow), and three cold lahars, which streamed 7.5 mi (12.1 km) down Mount Shasta's east flank via Ash Creek. A separate hot lahar went 12 mi (19 km) down Mud Creek. This eruption was thought to have been observed by the explorer La Pérouse, from his ship off the California coast, in 1786, but this has been disputed.[4]Estatut volcanic modificar
Durant las 10 000 darrièras annadas, lo mont esclatèt en mejan de cada 800 ans, mas al cors de las 4 500 darrièras annadas, lo volcan esclatèt en mejan de cada 600 ans. La darrièra erupcion importanta sus lo mont Shasta pòt èsser agut luòc i a environ dos sègles.[2]
Tèxte anglés de traduire :
USGS seismometers and GPS receivers operated by UNAVCO form the monitoring network for Mount Shasta. The volcano has been relatively quiet for at least the past 15 years, with only a handful of small magnitude earthquakes and no demonstrable ground deformation. Although geophysically quiet, periodic geochemical surveys indicate that volcanic gas emanates from a fumarole at the summit of Mount Shasta from a deep-seated reservoir of partly molten rock. [5]
Mount Shasta can release volcanic ash, pyroclastic flows or dacite and andesite lava. Its deposits can be detected under nearby small towns. Mount Shasta has an explosive, eruptive history. There are fumaroles on the mountain, which show Mount Shasta is still alive.Modèl:Citation needed
The worst-case scenario for an eruption is a large pyroclastic flow, similar to that which occurred in the 1980 eruption of Mount St. Helens. Since there is ice, such as Whitney Glacier and Mud Creek Glacier, lahars would also result. Ash would probably blow inland, perhaps as far as eastern Nevada. There is a small chance an eruption could result in a collapse of the mountain, as happened when Mount Mazama in Oregon collapsed to form what is now called Crater Lake, but this is of much lower probability.Modèl:Citation needed
The United States Geological Survey monitors Mount Shasta[6] and rates it as a very high-threat volcano.[7]
Istòria modificar
Tèxte anglés de traduire :
The oldest-known human settlement in the area dates to about 7,000 years ago.Modèl:Citation needed
At the time of Euro-American contact in the 1820s, the Native American tribes who lived within view of Mount Shasta included the Shasta, Okwanuchu, Modoc, Achomawi, Atsugewi, Karuk, Klamath, Wintu, and Yana tribes.
The historic eruption of Mount Shasta in 1786 may have been observed by Lapérouse, but this is disputed. Although perhaps first seen by Spanish explorers, the first reliably reported land sighting of Mount Shasta by a European or American was by Peter Skene Ogden (a leader of a Hudson's Bay Company trapping brigade) in 1826. In 1827, the name "Sasty" or "Sastise" was given to nearby Mount McLoughlin by Ogden.[8] An 1839 map by David Burr lists the mountain as Rogers Peak.[9] This name was apparently dropped, and the name Shasta was transferred to present-day Mount Shasta in 1841, partly as a result of work by the United States Exploring Expedition.
Beginning in the 1820s, Mount Shasta was a prominent landmark along what became known as the Siskiyou Trail, which runs at Mount Shasta's base. The Siskiyou Trail was on the track of an ancient trade and travel route of Native American footpaths between California's Central Valley and the Pacific Northwest.
The California Gold Rush brought the first Euro-American settlements into the area in the early 1850s, including at Yreka, California and Upper Soda Springs. The first recorded ascent of Mount Shasta occurred in 1854 (by Elias Pearce), after several earlier failed attempts. In 1856, the first women (Harriette Eddy, Mary Campbell McCloud, and their party) reached the summit.[10][11]
By the 1860s and 1870s, Mount Shasta was the subject of scientific and literary interest. In 1854 John Rollin Ridge titled a poem "Mount Shasta." A book by California pioneer and entrepreneur James Hutchings, titled Scenes of Wonder and Curiosity in California, contained an account of an early summit trip in 1855.[12] The summit was achieved (or nearly so) by John Muir, Josiah Whitney, Clarence King, and John Wesley Powell. In 1877, Muir wrote a dramatic popular article about his surviving an overnight blizzard on Mount Shasta by lying in the hot sulfur springs near the summit.[13] This experience was inspiration to Kim Stanley Robinson's short story "Muir on Shasta".
The 1887 completion of the Central Pacific Railroad, built along the line of the Siskiyou Trail between California and Oregon, brought a substantial increase in tourism, lumbering, and population into the area around Mount Shasta. Early resorts and hotels, such as Shasta Springs and Upper Soda Springs, grew up along the Siskiyou Trail around Mount Shasta, catering to these early adventuresome tourists and mountaineers.
In the early 20th century, the Pacific Highway followed the track of the Siskiyou Trail to the base of Mount Shasta, leading to still more access to the mountain. Today's version of the Siskiyou Trail, Interstate 5, brings thousands of people each year to Mount Shasta.
From February 13–19, 1959, the Mount Shasta Ski Bowl obtained the record for the most snowfall during one storm in the U.S., with a total of 15.75 feet (480 cm).[14]
Mount Shasta was declared a National Natural Landmark in December 1976.[15]
Legends
The lore of some of the Klamath Tribes in the area held that Mount Shasta is inhabited by the Spirit of the Above-World, Skell, who descended from heaven to the mountain's summit at the request of a Klamath chief. Skell fought with Spirit of the Below-World, Llao, who resided at Mount Mazama by throwing hot rocks and lava, probably representing the volcanic eruptions at both mountains.[16]
Italian settlers arrived in the early 1900s to work in the mills as stonemasons and established a strong Catholic presence in the area. Many other faiths have been attracted to Mount Shasta over the years—more than any other Cascade volcano.Modèl:Citation needed Mount Shasta City and Dunsmuir, California, small towns near Shasta's western base, are focal points for many of these, which range from a Buddhist monastery (Shasta Abbey, founded by Houn Jiyu-Kennett in 1971) to modern-day Native American rituals. A group of Native Americans from the McCloud River area practice rituals on the mountain.[17]
Mount Shasta has also been a focus for non-Native American legends, centered on a hidden city of advanced beings from the lost continent of Lemuria.[18] The legend grew from an offhand mention of Lemuria in the 1880s, to a description of a hidden Lemurian village in 1925. In 1931, Wisar Spenle Cerve wrote Lemuria: the lost continent of the Pacific, published by the Rosicrucians, about the hidden Lemurians of Mount Shasta that cemented the legend in many readers' minds.[18]
In August 1987, believers in the spiritual significance of the Harmonic Convergence described Mount Shasta as one of a small number of global "power centers".[19] Mount Shasta remains a focus of "New Age" attention.[20]
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- (en) Aqueste article es parcialament o en totalitat eissit d’una traduccion de l’article de Wikipèdia en anglés intitolat « Mount Shasta ».
- ↑ MT SHASTANGS Data Sheet
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- ↑ https://pubs.er.usgs.gov/publication/sir20185159%7CCalifornia’s Exposure to Volcanic Hazards Scientific Investigations Report 2018-5159 Prepared in cooperation with the California Governor’s Office of Emergency Services and the California Geological Surve
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- ↑ Modèl:Cite newspaper The Shasta Courier reprints from its files of 1856.
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