http://en.wikipedia.org/wiki/Mount_Shasta wrote:
<<Mount Shasta (Úytaahkoo in Karuk or "White Mountain") is located in Siskiyou County and at 14,179 feet (4,322 m) is the second highest peak in the Cascades and the fifth highest in California. Mount Shasta has an estimated volume of 85 cubic miles (350 km3) which makes it the most voluminous stratovolcano in the Cascade Volcanic Arc. Mount Shasta is not connected to any nearby mountain. It rises abruptly and stands nearly 10,000 feet (3,000 m) above the surrounding terrain. Because of this great prominence, it casts a gigantic shadow at sunrise.
The mountain has attracted the attention of poets, authors, and presidents. Shasta was memorably described by the poet Joaquin Miller: "Lonely as God, and white as a winter moon, Mount Shasta starts up sudden and solitary from the heart of the great black forests of Northern California."
Naturalist and author John Muir said of Shasta: "When I first caught sight of it over the braided folds of the Sacramento Valley, I was fifty miles away and afoot, alone and weary. Yet all my blood turned to wine, and I have not been weary since."
The mountain consists of four overlapping volcanic cones which have built a complex shape, including the main summit and the prominent satellite cone of 12,330-foot (3,760 m) Shastina, which has a visibly conical form. If Shastina were a separate mountain, it would rank as the third-highest peak of the Cascade Range.
Mount Shasta's surface is relatively free of deep glacial erosion except, paradoxically, for its south side where Sargents Ridge runs parallel to the U-shaped Avalanche Gulch. This is the largest glacial valley on the volcano, although it does not presently have a glacier in it.
There are seven named glaciers on Shasta, with the four largest (Whitney, Bolam, Hotlum, and Wintun) radiating down from high on the main summit cone to below 10,000 feet (3,000 m) primarily on the north and east sides. The Whitney Glacier is the longest and the Hotlum is the most voluminous glacier in the state of California. Three of the smaller named glaciers occupy cirques near and above 11,000 feet (3,400 m) on the south and southeast sides, including the Watkins, Konwakiton, and Mud Creek Glaciers.
There are many buried glacial scars on the mountain which were originally 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 that Shastina developed after the last ice age.
About 593,000 years ago andesitic lavas erupted in what is now Mount Shasta's western flank near McBride Spring. Over time an ancestral Shasta stratovolcano was built to large but unknown height; sometime between 300,000 to 360,000 years ago the entire north side of the volcano collapsed, creating an enormous landslide or debris avalanche, 6.5 cubic miles (27 km3) in volume. The slide flowed northwestward into Shasta Valley where the Shasta River now cuts through the 28 miles (45 km) long flow.
What remains of the oldest of 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 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.
Since then the Shastina cone has been built by mostly pyroxene andesite lava flows. Some 9,500 years ago, these flows reached about 6.8 miles (10.9 km) south and 3 miles (4.8 km) north of the area now occupied by nearby Black Butte (see image at right). 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 square miles (110 km2), including large parts of what is now Mount Shasta, California and Weed, California. Diller Canyon (400 feet (120 m) deep and 0.25 miles (400 m) wide) is an avalanche chute that was probably carved into Shastina's western face by these flows.
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 feet (150 m) thick Military Pass flow, extends 5.5 miles (8.9 km) down its northwest face. Since the creation of the Hotlum Cone, a dacite dome intruded the cone and now forms the summit. The rock at the 600 feet (180 m) wide summit crater has been extensively hydrothermally altered by sulfurous hot springs and fumaroles there (only a few examples still remain). In the last 8,000 years, the Hotlum Cone has erupted at least eight or nine times. About 200 years ago the last significant Shasta eruption came from this cone and created a pyroclastic flow, a hot lahar (mudflow), and three cold lahars, which streamed 7.5 miles (12.1 km) down Shasta's east flank via Ash Creek. A separate hot lahar went 12 miles (19 km) down Mud Creek. This eruption was observed by the explorer La Pérouse, from his ship off the California coast, in 1786.[3]
During the last 10,000 years Shasta has erupted an average of every 800 years but in the past 4,500 years the volcano has erupted an average of every 600 years. The last significant eruption on Shasta may have occurred 200 years ago, as noted above. Mount Shasta can release volcanic ash, pyroclastic flows or dacite and andesite lava. Its deposits can be detected under nearby small towns totaling 20,000 in population. Shasta has an explosive, eruptive history. There are fumaroles on the mountain, which show that Shasta is still alive. The worst case scenario for an eruption is a large pyroclastic flow, such as what 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 that an eruption could also be bigger resulting 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. The United States Geological Survey considers Shasta a dormant volcano, which will erupt again. It is impossible to pinpoint the date of next eruption, but it likely will occur within the next several hundred years.
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 lore of some of the American Indians in the area held that Shasta is inhabited by the spirit chief Skell who descended from heaven to the mountain's summit.
The historic eruption of Mount Shasta in 1786 may have been observed by la Perouse, 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. 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 located on the track of an ancient trade and travel route of Native American footpaths between California's Central Valley and the Pacific Northwest. By the 1860s and 1870s, Shasta was the subject of scientific and literary interest. 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 achieved) by John Muir, Josiah Whitney, Clarence King, and John Wesley Powell. In 1877, Muir wrote a dramatic popular article about an experience in which he survived an overnight blizzard on Shasta by lying in the hot sulfur springs found near the summit.>>
A Graceful Arc
