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48-472: Long Valley was formed 760,000 years ago when a very large eruption released hot ash that later cooled to form the Bishop tuff that is common to the area. The eruption emptied the magma chamber under the area to the point of collapse. The second phase of the eruption released pyroclastic flows that burned and buried thousands of square miles. Ash from this eruption blanketed much of the western part of what

96-482: A fumarole on the slopes of the mountain while attempting to fence it off. Ultra-Plinian Plinian eruptions or Vesuvian eruptions are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in 79 AD , which destroyed the ancient Roman cities of Herculaneum and Pompeii . The eruption was described in a letter written by Pliny the Younger , after the death of his uncle Pliny

144-478: A 25-mile (40 km)-long volcanic chain situated along a narrow, north–south-trending fissure system extending along the western rim of the caldera from Mammoth Mountain to the north shore of Mono Lake. The Mono-Inyo Craters erupted from 40,000 to 600 years ago, from a magma source separate from the Long Valley Caldera. The caldera has an extensive hydrothermal system. Casa Diablo Hot Springs at

192-404: A better sight of this very uncommon appearance. A cloud, from which mountain was uncertain, at this distance (but it was found afterwards to come from Mount Vesuvius), was ascending, the appearance of which I cannot give you a more exact description of than by likening it to that of a pine tree, for it shot up to a great height in the form of a very tall trunk, which spread itself out at the top into

240-428: A cutoff for an ultra-Plinian eruption. In the criteria of Volcanic Explosivity Index , recognizing an eruption as ultra-Plinian would make it at least VEI-5 or higher. The threshold for ultra-Plinian eruptions is defined by an eruptive column height of 45 km (28 mi), or 41 km (25 mi) more recently. The few instances of eruptions that lie at the transition between Plinian and ultra-Plinian include

288-632: A dozen people have died in Hot Creek since the late 1960s, but most of these deaths happened to people who ignored the numerous warning signs and attempted to use the hydrothermal pools as hot tubs (like the stream portion of the creek, these pools alternate in temperature but the eruptions in the pools are of super-heated water in already very hot water). Recent geothermal instability has led to its temporary closure for swimming. Officials are unsure of when (if ever) Hot Creek will officially reopen for swimming. Hydrothermal activity has altered many rocks in

336-554: A man of such learning and research as my uncle extraordinary and worth further looking into. Pliny the Elder set out to rescue the victims from their perilous position on the shore of the Bay of Naples , and launched his galleys , crossing the bay to Stabiae (near the modern town of Castellammare di Stabia). Pliny the Younger provided an account of his death, and suggested that he collapsed and died through inhaling poisonous gases emitted from

384-425: A pyroclastic flow traveled for several hundreds of meters above the sea. A pyroclastic flow can interact with a body of water to form a large amount of mud, which can then continue to flow downhill as a lahar . This is one of several mechanisms that can create a lahar. In 1963, NASA astronomer Winifred Cameron proposed that the lunar equivalent of terrestrial pyroclastic flows may have formed sinuous rilles on

432-438: A research team at Kiel University , Germany, of pyroclastic flows moving over the water. When the reconstructed pyroclastic flow (stream of mostly hot ash with varying densities) hit the water, two things happened: the heavier material fell into the water, precipitating out from the pyroclastic flow and into the liquid; the temperature of the ash caused the water to evaporate, propelling the pyroclastic flow (now only consisting of

480-412: A sort of branches; occasioned, I imagine, either by a sudden gust of air that impelled it, the force of which decreased as it advanced upwards, or the cloud itself being pressed back again by its own weight, expanded in the manner I have mentioned; it appeared sometimes bright and sometimes dark and spotted, according as it was either more or less impregnated with earth and cinders. This phenomenon seemed to

528-465: Is now the United States . The caldera is a giant bowl-shaped depression, approximately 20 mi (32 km) long, surrounded by mountains except to the southeast. The elevation of the bottom of the bowl ranges from 6,500 to 8,500 ft (2,000 to 2,600 m), being higher in the west. Near the center of the bowl, magmatic uplift has formed a resurgent dome . The southeastern slope from

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576-548: Is sometimes abbreviated to PDC (pyroclastic density current). Several mechanisms can produce a pyroclastic flow: Flow volumes range from a few hundred cubic meters to more than 1,000 cubic kilometres (240 cu mi). Larger flows can travel for hundreds of kilometres, although none on that scale has occurred for several hundred thousand years. Most pyroclastic flows are around one to ten cubic kilometres ( 1 ⁄ 4 – 2 + 1 ⁄ 2  cu mi) and travel for several kilometres. Flows usually consist of two parts:

624-486: Is unlikely to produce large-scale eruptions in the future. The Long Valley volcano is unusual in that it has produced eruptions of both basaltic and silicic lava in the same geological place. Water from the Owens River filled the caldera to a depth of 300 m (984 ft) as of 600,000 years ago. At that time, the lake surface was at an elevation near 7,500 ft (2,286 m). The lake drained sometime in

672-412: Is usually dacitic or rhyolitic , rich in silica. Basaltic , low-silica lavas rarely produce Plinian eruptions unless specific conditions are met (low magma water content <2%, moderate temperature, and rapid crystallization); a recent basaltic example is the 1886 eruption of Mount Tarawera on New Zealand's North Island . Pliny the Younger described the initial observations of his uncle, Pliny

720-529: The 1883 eruption of Krakatoa , supported by experimental evidence, shows that pyroclastic flows can cross significant bodies of water. However, that might be a pyroclastic surge , not flow, because the density of a gravity current means it cannot move across the surface of water. One flow reached the Sumatran coast as far as 48 kilometres (26 nautical miles) away. A 2006 BBC documentary film, Ten Things You Didn't Know About Volcanoes , demonstrated tests by

768-577: The Alkali Lakes area. The largest springs are in Hot Creek Gorge where about 250 L (66 US gal) per second of thermal water discharge and account for about 80% of the total thermal water discharge in the caldera. At the other extreme are springs at Hot Creek Fish Hatchery which contain a small component (2–5%) of thermal water that raises water temperatures about 5 °C (9.0 °F) higher than background temperatures. Use of

816-641: The P3 phase of 1257 Samalas eruption , 1991 eruption of Mount Pinatubo , the Plinian phase of the Campanian Ignimbrite , Tsankawi Pumice Bed of Tshirege Member of Bandelier Tuff , and the 1902 eruption of Santa María . The once unequivocal ultra-Plinian classification of the Hatepe eruption has been called into question, with recent evidence showing that it is an artifact of an unrecognized shift in

864-639: The basal flow hugs the ground and contains larger, coarse boulders and rock fragments, while an extremely hot ash plume lofts above it because of the turbulence between the flow and the overlying air, admixing and heating cold atmospheric air causing expansion and convection. Flows can deposit less than 1 meter to 200 meters in depth of loose rock fragment. The kinetic energy of the moving cloud will flatten trees and buildings in its path. The hot gases and high speed make them particularly lethal, as they will incinerate living organisms instantaneously or turn them into carbonized fossils: Testimonial evidence from

912-404: The Elder , of the 79 AD eruption of Mount Vesuvius : On August 24th, about one in the afternoon, my mother desired him to observe a cloud which appeared of a very unusual size and shape. He had just taken a turn in the sun and, after bathing himself in cold water, and making a light luncheon, gone back to his books: he immediately arose and went out upon a rising ground from whence he might get

960-574: The Elder . Plinian/Vesuvian eruptions are marked by columns of volcanic debris and hot gases ejected high into the stratosphere , the second layer of Earth's atmosphere. The key characteristics are the ejection of a large amount of pumice and very powerful continuous gas-driven eruptions. Short eruptions can end in less than a day, but longer events can continue for several days or months. The longer eruptions begin with production of clouds of volcanic ash, sometimes with pyroclastic surges . The amount of magma ejected can be so large that it depletes

1008-574: The Long Valley volcanism are still largely unexplained and are therefore a matter of much ongoing research. Long Valley is not above a hotspot , such as those which fuel Yellowstone Caldera or the volcanoes of Hawaii ; nor is it the result of subduction such as that which produces the volcanism of the Cascades . The known volcanic history of Long Valley Caldera area started a few million years ago when magma began to collect several miles below

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1056-454: The air where winds distributed it as far away as eastern Nebraska and Kansas . The eruption initially produced a caldera 2–3 km (1.2–1.9 mi) deep. However, much of the ejecta went straight up, fell down, and filled the initial caldera about two-thirds full. Subsequent eruptions from the Long Valley magma chamber were confined within the caldera with extrusions of relatively hot (crystal-free) rhyolite 700,000 to 600,000 years ago as

1104-513: The base of the resurgent dome hosts a geothermal power plant . Hot Creek cuts into part of the resurgent dome and passes through hot springs. The warm water of Hot Creek supports many trout, and is used at the Hot Creek Fish Hatchery. The creek was closed to swimming in 2006 after geothermal activity in the area increased. The area has a number of other hot springs, some of which are open to bathers . The tectonic causes of

1152-653: The caldera down towards Bishop, California , is filled with the Bishop Tuff , solidified ash that was ejected during the eruption that created the caldera. The Bishop tuff is 1,500 metres (4,900 ft) thick in the caldera floor, and is cut by the Owens River Gorge, formed during the Pleistocene when the caldera filled with water and overtopped its rim. The rim of the caldera is formed from pre-existing rock, rising about 3,000 ft (910 m) above

1200-440: The caldera floor was uplifted to form the resurgent dome followed by extrusions of cooler, crystal-rich moat rhyolite at 200,000-year intervals (500,000, 300,000, and 100,000 years ago) in clockwise succession around the dome. The declining volcanic activity and increasingly crystalline lava extruded over the last 650,000 years, as well as other trends, suggest that the magma reservoir under the caldera has now largely crystallized and

1248-436: The caldera floor. However, the eastern rim is lower, only about 500 ft (150 m). Mammoth Mountain is a lava dome complex west of the structural rim of the caldera, consisting of about 12 rhyodacite and dacite overlapping domes. These domes formed in a long series of eruptions from 110,000 to 57,000 years ago, building a volcano that reaches 11,059 ft (3,371 m) in elevation. The Mono–Inyo Craters are

1296-423: The caldera floor. These events marked the onset of the latest period of caldera unrest that is ongoing. This ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera accompanied by changes in thermal springs and gas emissions. After the quake, a secondary access road was created as a potential escape route for the town of Mammoth Lakes. Its name at first

1344-544: The caldera, is noted for its fishing. The nearest hotel accommodations to the caldera are in Mammoth Lakes, California . There are also campgrounds scattered throughout the caldera, and in the mountains near the edge of the caldera. In April 2006, three members of the Mammoth Mountain Ski Area ski patrol died while on duty. All three died from suffocation by carbon dioxide when they fell into

1392-568: The caldera, transforming them into travertine and clay . At the Huntley clay mine white chalky clay called kaolinite is mined; the kaolinite is exposed on the resurgent dome and appears as a brilliant white band. The largest tourist attraction in the caldera is the Mammoth Mountain Ski Area : the area offers skiing and snowboarding in the winter, and mountain biking in the summer. The Hot Creek tourist attraction

1440-679: The dark is nuée ardente (French, "burning cloud"); this was notably used to describe the disastrous 1902 eruption of Mount Pelée on Martinique , a French island in the Caribbean. Pyroclastic flows that contain a much higher proportion of gas to rock are known as "fully dilute pyroclastic density currents" or pyroclastic surges . The lower density sometimes allows them to flow over higher topographic features or water such as ridges, hills, rivers, and seas. They may also contain steam, water, and rock at less than 250 °C (480 °F); these are called "cold" compared with other flows, although

1488-457: The eastern half of the caldera where land-surface elevations are relatively low; fumaroles exist primarily in the western half where elevations are higher. Mineral deposits from thermal activity are found on an uplifted area called the resurgent dome, at Little Hot Creek springs, Hot Creek Gorge , and other locations in the south and east moats of the caldera. Hot springs discharge primarily in Hot Creek Gorge, along Little Hot Creek , and in

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1536-498: The hydraulic gradient, from the west to the southeast around the resurgent dome and then eastward to discharge points along Hot Creek and around Crowley Lake . Reservoir temperatures in the volcanic fill decline from 220 °C (428 °F) near the Inyo Craters to 50 °C (122 °F) near Crowley Lake due to a combination of heat loss and mixing with cold water. Hot Creek has been a popular swimming hole for decades. Over

1584-488: The last 100,000 years after it overtopped the southern rim of the caldera, eroded the sill, and created the Owens River Gorge . A human-made dam in the gorge has created Lake Crowley , a partial restoration of the original lake. Since the great eruption, many hot springs developed in the area, and the resurgent dome has uplifted. During the last ice age , glaciers filled the canyons leading to Long Valley, but

1632-492: The lighter material) along on a bed of steam at an even faster pace than before. During some phases of the Soufriere Hills volcano on Montserrat, pyroclastic flows were filmed about 1 km ( 1 ⁄ 2  nmi) offshore. These show the water boiling as the flow passes over it. The flows eventually built a delta, which covered about 1 km (250 acres). Another example was observed in 2019 at Stromboli when

1680-600: The magma chamber below, causing the top of the volcano to collapse, resulting in a caldera . Fine ash and pulverized pumice can be deposited over large areas. Plinian eruptions are often accompanied by loud sounds. The sudden discharge of electrical charges accumulated in the air around the ascending column of volcanic ashes also often causes lightning strikes, as depicted by the English geologist George Julius Poulett Scrope in his painting of 1822 or observed during 2022 Hunga Tonga–Hunga Ha'apai eruption and tsunami . The lava

1728-499: The major ( volcanic explosivity index (VEI) 7) eruption of the area 760,000 years ago, which released 600 cubic kilometres (144 cu mi) of material from vents just inside the margin of the caldera. (The 1980 Mount St. Helens eruption was a VEI-5 eruption releasing 1.2 km (0.29 cu mi).) About half of this material was ejected in a series of pyroclastic flows of a very hot (1,500 °F (820 °C)) mixture of noxious gas, pumice , and volcanic ash that covered

1776-543: The most deadly of all volcanic hazards and are produced as a result of certain explosive eruptions ; they normally touch the ground and hurtle downhill or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. The word pyroclast is derived from the Greek πῦρ ( pýr ), meaning "fire", and κλαστός ( klastós ), meaning "broken in pieces". A name for pyroclastic flows that glow red in

1824-586: The nature of the potential hazards posed by this unrest and timely warning of an impending volcanic eruption, should it develop. Most, perhaps all, volcanic eruptions are preceded and accompanied by geophysical and geochemical changes in the volcanic system. Common precursory indicators of volcanic activity include increased seismicity, ground deformation , and variations in the nature and rate of gas emissions. The Long Valley Caldera hosts an active hydrothermal system that includes hot springs, fumaroles (steam vents), and mineral deposits. Hot springs exist primarily in

1872-504: The surface. Volcanic activity became concentrated in the vicinity of the present site of Long Valley Caldera 3.1 to 2.5 million years ago with eruptions of rhyodacite followed by high-silica rhyolite from 2.1 to 0.8 million years ago. After some time, a cluster of mostly rhyolitic volcanoes formed in the area. All told, about 1,500 sq mi (3,900 km) were covered by lava. All but one of these volcanoes, 1–2 million year old Glass Mountain (made of obsidian ), were destroyed by

1920-532: The surrounding area hundreds of feet deep. One lobe of this material moved south into Owens Valley , past present-day Big Pine, California . Another lobe moved west over the crest of the Sierra Nevada and into the drainage of the San Joaquin River . The rest of the pyroclastic material, along with 300 km (72 cu mi) of other matter, was blown as far as 25 mi (40 km) into

1968-436: The temperature is still lethally high. Cold pyroclastic surges can occur when the eruption is from a vent under a shallow lake or the sea. Fronts of some pyroclastic density currents are fully dilute; for example, during the eruption of Mount Pelée in 1902, a fully dilute current overwhelmed the city of Saint-Pierre and killed nearly 30,000 people. A pyroclastic flow is a type of gravity current ; in scientific literature, it

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2016-404: The valley floor was clear of ice. Excellent examples of terminal moraines can be seen at Long Valley. Laurel Creek, Convict Creek , and McGee Creek each have prominent moraines. In May 1980, a strong earthquake swarm that included four Richter magnitude 6 earthquakes struck the southern margin of the Long Valley Caldera. It was associated with a 10 in (250 mm) dome-shaped uplift of

2064-478: The volcano. His body was found interred under the ashes of the eruption with no apparent injuries on 26 August, after the plume had dispersed, confirming asphyxiation or poisoning. In 1980, volcanologist George P. L. Walker proposed Hatepe eruption as the representative of a new class called ultra-Plinian deposits, based on its exceptional dispersive power and eruptive column height. A dispersal index of 50,000 square kilometres (19,000 sq mi) has been proposed as

2112-400: The warm spring water in the hatchery has increased fish production because trout growth rates are faster in the warm water than in ambient stream temperatures in Long Valley. In hydrothermal systems the circulation of groundwater is driven by a combination of topography and heat sources. In Long Valley Caldera, the system is recharged primarily from snow -melt in the highlands around

2160-442: The western and southern rims of the caldera. The water from snow-melt and rainfall infiltrates to depths of a few kilometers (miles) where it is heated to at least 220 °C (428 °F) by hot rock near geologically young intrusions. Upflow occurs in the west moat where the heated water with lower density rises along steeply inclined fractures to depths of 1–2 km (0.62–1.24 mi). This hydrothermal fluid flows laterally, down

2208-571: The wind field rather than extreme eruptive vigor. Pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud ) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra ) that flows along the ground away from a volcano at average speeds of 100 km/h (30 m/s; 60 mph) but is capable of reaching speeds up to 700 km/h (190 m/s; 430 mph). The gases and tephra can reach temperatures of about 1,000 °C (1,800 °F). Pyroclastic flows are

2256-477: Was closed to swimming in 2006 due to increased geothermal activity. Hiking and off-road vehicle driving is available throughout the caldera, and in the glacial valleys of the Sherwin Range , immediately to the south of the caldera. Hikers can hike to several lakes in these glacial valleys, including Valentine Lake , Convict Lake , Lake Dorothy , and Laurel Lakes . Crowley Lake , at the south end of

2304-631: Was proposed as the "Mammoth Escape Route" but was changed to the Mammoth Scenic Loop after Mammoth area businesses and land owners complained. In 1982, the United States Geological Survey under the Volcano Hazards Program began an intensive effort to monitor and study geologic unrest in Long Valley Caldera. The goal is to provide residents and civil authorities with reliable information on

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