Misplaced Pages

#554445

110-598: Eruptions along the narrow fissure system under the chain began in the west moat of Long Valley Caldera 400,000 to 60,000 years ago. Mammoth Mountain was formed during this period. Multiple eruptions from 40,000 to 600 years ago created the Mono Craters and eruptions 5,000 to 500 years ago formed the Inyo volcanic chain. Lava flows 5,000 years ago built the Red Cones, and explosion pits on Mammoth Mountain were excavated in

220-405: A decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of the fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into

330-470: A fumarole on the slopes of the mountain while attempting to fence it off. Fault (geology) In geology , a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with the largest forming the boundaries between

440-860: A plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or the Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are

550-480: 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

660-525: A divided pair of lobes. Northwest Coulee is located northwest of North Coulee and was intruded by Upper Dome after the coulee solidified. Permanent pockets of ice from snowmelt have been found 75 to 147 feet (23 to 45 m) inside the coulees and domes. The Mono–Inyo chain of craters lies in east-central California, roughly parallel to the eastern escarpment of the Sierra Nevada mountain range. Volcanism and seismic activity in eastern California are

770-633: 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

880-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving

990-410: A fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing the seismic shaking and tsunami hazard to infrastructure and people in

1100-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear

1210-655: A growing lava dome may reach 3.1 to 6.2 miles (5 to 10 km) from the dome. A partial collapse of the steep-sided growing dome can send pyroclastic flows outward at least 3.1 miles (5 km). Taller domes tend to form larger pyroclastic flows that travel farther. Many recreational activities are available along the chain. The Mono Basin National Scenic Area visitor center is located near Mono Lake just off U.S. Route 395 . A bookstore, an information desk staffed by USDA Forest Service Rangers, and museum exhibits help to orient visitors. The Mono Lake Committee has

SECTION 10

#1732791849555

1320-478: A hill at the southern end of the field shows what Israel Russell called a " beach line ". The present elevation of this beach line is the level of the Mono Lake high stand before the formation of the northern Mono Craters, plus any surface deformation that has happened since that time. Stream-rounded stones are found on the volcanoes, and were lifted up as the volcanoes grew. Although glaciers were present throughout

1430-809: A result of two major geologic processes: northwest movement of the Pacific Plate with respect to the North American Plate along the San Andreas Fault system near the coast, and east–west extension of the crust that formed the Basin and Range Province . In the Long Valley region, where the craters are located, basin and range extension encroaches onto the thick and stable crust of the Sierra Nevada. Basement rock under

1540-606: A staffed office and visitor information center in Lee Vining on the corner of U.S. Route 395 and 3rd Street. Information on camping, hiking, guided and self-guided tours can all be obtained at either location. Multiple paved roads surround the Mono-Inyo craters. U.S. 395 is a scenic route that roughly parallels the Mono–Inyo Craters volcanic chain. California State Route 120 approaches the northern and eastern parts of

1650-465: Is Mammoth Lakes . The craters are in the Great Basin geographic area. The Mono Craters are a 10.5-mile (17 km) chain of at least 27 volcanic domes, three large glass flows called coulees and various explosion pits and other associated volcanic features. The domes of the chain lie on a roughly north–south-trending arc that is concave to the west and located south of Mono Lake. The highest of

1760-456: Is "Earthquake Fault", a fissure up to 10 feet (3 m) wide that cuts 60 to 70 feet (18 to 21 m) into glassy rhyolite lava flows. The fissure was formed by stretching induced by the intrusion of the Inyo dike. Stairs to the bottom of the fissure were removed after being damaged by earthquakes in 1980. Several Mono–Inyo-related explosion pits are on Mammoth Mountain. The Red Cones , south of Mammoth Mountain, are basaltic cinder cones and are

1870-473: Is 2.25 miles (3.6 km) long, 0.75 miles (1.2 km) wide and has a volume of 0.1 cubic miles (0.4 km); making it the largest Mono Craters coulee in volume. South Coulee originates from the crest of the Mono Domes, about 3 miles (5 km) from the southern end, flows down its east and west flanks and terminates at its foot. North Coulee is nearly as large, flows mostly to the east and terminates in

1980-466: Is not related to the caldera's volcanism. South of the Inyo volcanic chain are other features related to the dike system responsible for creating the craters, volcanoes and lava flows. These include a north–south trend of fault scarps up to 20 feet (6 m) high and pull-apart cracks or fissures in the earth. These fissures are not technically faults because little or no vertical or horizontal movement has occurred along them. Most notable among these

2090-412: Is now Long Valley. Rhyolitic eruptions occurred in and around Glass Mountain in the same area from 2.1 to 0.8 million years ago. Volcanic ash from the massive (600 cubic kilometres or 140 cubic miles of ejecta) eruption of Long Valley Caldera some 760,000 years ago is preserved in the thick Bishop Tuff that covers much of the region. Eruptions of basalt and andesite 400,000 to 60,000 years ago in

2200-466: 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

2310-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of

SECTION 20

#1732791849555

2420-434: Is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas the brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when

2530-537: Is twofold; an outer tuff ring (forming a classic crater) and an inner plug, or dome of rhyolite, pumice and obsidian created from lavas. In this case, heat from the magma feeding Panum flashed groundwater to steam to create the tuff ring before lava reached the surface. Other Mono Craters also were formed in this manner, but their plug domes grew larger than their tuff ring craters. The domes have steep sides and are flanked by slopes of scree consisting of large angular and glass-rich rocks. Devil's Punch Bowl, located south of

2640-489: 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

2750-577: 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

2860-463: The Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with a major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in

2970-675: The Los Angeles Aqueduct system from their natural outlets in Mono Lake started in 1941 after a water tunnel was cut under the Mono Craters. Mono Lake Volcanic Field and a large part of the Mono Craters gained some protection under Mono Basin National Forest Scenic Area in 1984. Resource use along all of the chain is managed by the United States Forest Service as part of Inyo National Forest . Various activities are possible along

3080-413: The "loneliest spot on earth ... little graced with the picturesque." Naturalist John Muir explored the area in 1869. He described the "Mono Desert" as a "... country of wonderful contrasts. Hot deserts bounded by snow-laden mountains,—cinders and ashes scattered on glacier-polished pavements,—frost and fire working together in the making of beauty. In the lake are several volcanic islands, which show that

3190-528: The 1930s within Mono Basin and Owens Valley in order to control water rights . Excavation of an 11.5-mile (18.5 km) water tunnel under the southern part of the Mono Craters dome complex started in 1934 and was completed in 1941. Tunnel workers had to deal with loose and often water-charged gravels, pockets of carbon dioxide gas and flooding. About one man was lost for each mile excavated. Water diverted from its natural outlet in Mono Lake passes through

3300-570: The 19th century to exploit bonanzas. The largest of these, Bodie (north of Mono Lake), was founded in the late 1870s and grew large enough to need a tree mill, which was located at Mono Mills , immediately northeast of Mono Domes. Timberland to the east of the Mono Craters was clearcut for wood. As part of the California Water Wars , the Los Angeles Department of Water and Power purchased large tracts of land in

3410-647: The Inyo Craters, proper. The Inyo Craters are open pits in a forested area that are about 600 feet (180 m) across and 100 to 200 feet (30 to 60 m) deep, each with small ponds covering their floors. A quarter mile (half kilometer) north of these is another explosion pit on top of Deer Mountain. Farther north of these craters are five lava domes , including Deadman Creek Dome, Glass Creek Dome, Obsidian Dome, and Wilson Butte. These domes are composed of gray rhyolite , frothy pumice , and black obsidian . The Inyo volcanic chain extends into Long Valley Caldera but

Mono–Inyo Craters - Misplaced Pages Continue

3520-450: The Inyo part of the chain. The last recorded volcanic activity in the chain was at Mono Lake between the years 1720 and 1850. An intrusion of magma below the lake pushed lakebed sediments upward to form Paoha Island . Exposed rhyolite is on the north part of the island, and a group of seven dacite cinder cones and a lava flow are on the northeastern corner. Steam rose in columns hundreds of feet high (tens of meters) from Hot Spring Cove on

3630-514: 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

3740-426: The Mono Craters domes is Crater Mountain (elevation 9,172 feet or 2,796 m), which rises 2,400 feet (730 m) above Pumice Valley to the west. Associated volcanic features are located in Mono Lake ( Paoha and Negit Islands ) and on its north shore (Black Point). The coulees cluster north and south of the overlapping chain of domes. The Inyo volcanic chain stretches 6 miles (10 km) from Wilson Butte to

3850-482: The Mono Craters magma reservoir. Basaltic andesite lava built the Red Cones, two small cinder cones 6.2 miles (10 km) southwest of Mammoth Lakes, around 8,500 before present. The five Mammoth Mountain Craters are a set of explosion pits that trend west-north-west for 1.6 miles (2.5 km) near the northern flank of Mammoth Mountain. None of the Mono Craters near the lake show the effects of wave erosion, but

3960-420: The Mono Craters. About 660 feet (200 m) of subsidence has occurred within a ring fracture system centered on Pumice Valley west of the chamber in the last 700,000 years. The Mono Craters sit atop a 7.5-mile (12 km)-long arc on the eastern side of the 11-mile (18 km)-wide ring-fracture system. Magma feeding the domes may have exploited arc-shaped fissures around an intrusion of granitic rock deep below

4070-490: The Mono Craters. Black Point, today on the north shore of Mono Lake, is a flattened volcanic cone of basaltic debris that formed under the surface of a much deeper Mono Lake about 13,300 years ago, during the most-recent glacial period . Several eruptive episodes from 1,600 to 270 years before present in Mono Lake formed Negit Island. The magma reservoir feeding the Mono Lake Volcanic Field is unrelated to

4180-591: The Mono Domes, including Panum Crater . Mammoth Scenic Loop approaches the Inyo Craters. Direct access to the Mono—Inyo Craters requires driving on unpaved roads, then walking. The town of Mammoth Lakes and Mammoth Mountain are located near the southern end of the chain. Mammoth Mountain Ski Area is located nearby and gondola rides can be taken year-round (weather permitting) to the mountain's summit. The summit of Mammoth Mountain provides panoramic views of

4290-430: The Mono Lake region. The tephra were carried by the wind and deposited in a layer 8 inches (20 cm) deep 20 miles (32 km) from the vents and 2 inches (5 cm) deep 50 miles (80 km) away. Pyroclastic flows of hot clouds of gas, ash and pulverized lava erupted from these vents in narrow tongues that extended up to 5 miles (8 km) away and covered 38 square miles (100 km). Rhyolite lava oozed out of

4400-478: The Mono Valley (1889), which included a topographic survey by Willard D. Johnson, was the first thorough scientific description of Mono Lake and its volcanic features. Russell named the Mono Craters and wrote: "The attention of every one who enters Mono Valley is at once attracted by the soft, pleasing colors of these craters as well as by the symmetry and beauty of their forms. They are exceptional features in

4510-465: The Mono–Inyo Craters. Ash and rock fragments (tephra) may accumulate to a thickness of 33 feet (10 m) near an erupting Mono–Inyo vent. Downwind accumulations of tephra may exceed 7.9 inches (20 cm) at a distance of 22 miles (35 km) and 2.0 inches (5 cm) at 53 miles (85 km). Winds in the area tend to blow toward an east or northeasterly direction more than 50 percent of the time, and toward any easterly direction more than 80 percent of

Mono–Inyo Craters - Misplaced Pages Continue

4620-590: The Mono–Inyo chain consists of the same granitic and metamorphic rock that make up the Sierra Nevada. Above that layer are basaltic grading to rhyolitic volcanic rocks that are 3.5 million to less than 760,000 years old. Volcanism occurred north of the chain, in the Bodie Hills , as far back as 28 million years. Nearly all the rock east of the Sierra Nevada in the Mono Basin area is volcanic in origin. Volcanoes erupted from 3.6 to 2.3 million years ago near what

4730-432: The Sierra Nevada, they did not reach as far down as the Mono Craters. The most recent eruptive episode on the Mono Craters occurred sometime between the years 1325 and 1365. A vertical sheet-like mass of magma, called a dike, caused groundwater to explosively flash to steam, creating a line of vents 4 miles (6 km) long. A mix of ash and pulverized rock, called tephra, covered about 3,000 square miles (8,000 km) of

4840-619: The Sierra crest from the Pacific Ocean through the San Joaquin Gap. Temperatures in Mono Basin range from average winter lows of 20 to 28 °F (−7 to −2 °C) to average summer highs of 75 to 84 °F (24 to 29 °C). Temperatures near the Inyo volcanic chain and Mammoth Lakes area range from winter average lows of 16 to 21 °F (−9 to −6 °C) to summer average highs of 70 to 78 °F (21 to 26 °C). Most of

4950-454: 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

5060-404: The area. The region has been used by humans for centuries. Obsidian was collected by Mono Paiutes for making sharp tools and arrow points. Glassy rock continues to be removed in modern times for use as commercial scour and yard decoration. Mono Mills processed timber felled on or near the volcanoes for the nearby boomtown Bodie in the late 19th to early 20th centuries. Water diversions into

5170-517: 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

5280-655: 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

5390-441: 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

5500-427: 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

5610-442: 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

SECTION 50

#1732791849555

5720-544: 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

5830-568: 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

5940-571: The chain, including hiking, bird watching, canoeing, skiing, and mountain biking. The Mono–Inyo Craters form a volcanic chain in Eastern California that sits along a narrow north–south-trending fissure system extending from the north shore of Mono Lake through the western Long Valley Caldera , south of Mammoth Mountain . The chain is within the Inyo National Forest and Mono County ; the nearest incorporated community

6050-484: The chain. This magma chamber is separate from the magma chamber under Long Valley Caldera. The recent eruptions of the Mono Craters have been similar in volume and nearly identical in composition ("crystal-poor high-silica rhyolite") to those of Glass Mountain that preceded the Long Valley Caldera-forming eruption. It has been suggested that the Mono Craters volcanism may represent an early stage in

6160-414: The craters and domes of the Mono–Inyo volcanic chain, Mono Lake, the Sierra Nevada and Long Valley Caldera. Mono Lake itself has its own set of activities, including walking tours among towers of tufa , boat tours of the lake, and birdwatching opportunities. The lake is too salty to support any fish, but fishing is possible in streams that feed Mono Lake. Additional activities include hiking around and on

6270-775: The craters and domes, and mountain biking outside of the Scenic Area boundaries. [REDACTED]  This article incorporates public domain material from websites or documents of the United States Geological Survey . Long Valley Caldera Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain . The valley is one of the Earth's largest calderas , measuring about 20 mi (32 km) long (east-west), 11 mi (18 km) wide (north-south), and up to 3,000 ft (910 m) deep. Long Valley

6380-414: The crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of a hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through

6490-411: The development of a future caldera. Repeated eruption of dacite and rhyodacite from vents on the southwest rim of the caldera from 220,000 to 50,000 years ago formed Mammoth Mountain, a volcano composed of overlapping lava domes . Eruptions of dacite and rhyodacite occurred in Mono Basin from 100,000 to 6,000 years ago. Multiple eruptions of silica -rich rhyolite from 40,000 to 600 years ago built

6600-502: The dike was significantly cracked and faulted. Explosive eruptions emanated from three separate vents in the summer of 1350 CE. Pieces of molten and solid rock were ejected, small craters were formed, and an eruption column rose above the vents. Pumice and ash covered an extensive area downwind, and about 1 inch (2.5 cm) of tephra was deposited where the town of Mammoth Lakes, California , now sits. A pyroclastic flow from South Deadman vent traveled about 3.7 miles (6 km). Some of

6710-433: The direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between the fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as

SECTION 60

#1732791849555

6820-458: 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

6930-409: The fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of a non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body,

7040-459: The fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of

7150-413: The fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on the direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and

7260-428: The footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms

7370-531: The footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other, is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near

7480-420: The fungi. Jeffrey pine forests also surround the Inyo volcanic chain and Mammoth Mountain. Mule deer , coyotes , black bears , yellow-bellied marmots , raccoons and mountain lions all have ranges that are coincident with forests that cover parts of the Mono–Inyo craters. Panum Crater is the northernmost volcano in the sequence and is a good example of both a tuff ring and a rhyolite dome. Its structure

7590-429: The geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in the gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of

7700-438: 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

7810-491: The implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering ,

7920-647: The island and the spring water was 150 °F (66 °C) when geologist Israel Russell visited the island in the early 1880s. People have used resources on and around the Mono–Inyo Craters for centuries. Mono Paiutes gathered obsidian from the Mono–Inyo Craters to make sharp tools and arrow points. Unworked obsidian was carried by the Mono Paiutes over passes in the Sierra Nevada to trade with other Native American groups. Chips of Mono–Inyo obsidian can still be found at many ancient mountain campsites. Gold rush –related boomtowns sprang up near Mono Basin in

8030-464: The largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining a fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where

8140-498: The last 1,000 years. Uplift of Paoha Island in Mono Lake about 250 years ago is the most recent activity. These eruptions most likely originated from small magma bodies rather than from a single, large magma chamber like the one that produced the massive Long Valley Caldera eruption 760,000 years ago. During the past 3,000 years, eruptions have occurred every 250 to 700 years. In 1980, a series of earthquakes and uplift within and south of Long Valley Caldera indicated renewed activity in

8250-488: 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

8360-455: The last 2,000 years and have the ability to produce explosive eruptions. About 20 eruptions have occurred on the Mono–Inyo Craters chain at intervals of 250 to 700 years during the past 5,000 years. Seismic soundings and lava composition indicate that these eruptions most likely originated from discrete and small magma bodies. The rate of eruption over the last 1,000 years has increased, with at least 12 eruptions occurring. All eruptions in

8470-567: The main dome complex, stopped forming at an earlier stage of development. It is a 1,200-foot (370 m) wide and 140-foot (43 m) deep explosion pit with a much smaller glass dome on its floor. The large North and South Coulee and the smaller Northwest Coulee consist of obsidian-rich rhyolite. They were formed from slow-moving lava that had a thin and brittle crust. Once the flow stopped, it formed steep sided tongues of sharp and angular rock that are typically 200 to 300 feet (60 to 90 m) thick and have scree piles along their base. South Coulee

8580-501: 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

8690-408: The miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In a reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of

8800-435: The most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to the original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to

8910-589: 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

9020-731: The northern half of the Mono Craters. Litigation and outreach by the Mono Lake Committee , the National Audubon Society and other conservation groups has helped to slow water diversions from tributaries feeding Mono Lake. The Long Valley to Mono Lake region is one of three areas in California that are in the United States Geological Survey's volcanic hazards program. These areas are in the program because they have been active in

9130-575: The open pits were filled with thick and slow-moving lava to form the South Deadman Creek, Glass Creek and Obsidian Flow domes. Others, such as the Inyo Crater Lakes near Deer Mountain, remained open and were later partially filled with water. Smaller explosion pits on the north side of Mammoth Mountain were also formed at this time. In the past 6,000 years, approximately 0.19 cubic miles (0.8 km) of magma has been erupted from

9240-494: The opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by the fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and

9350-526: The past 5,000 years from the Mono–Inyo Craters have expelled less than 0.24 cubic miles (1 km) of magma . Future eruptions in the area will likely be similar in size to the small to moderate events of the past 5,000 years. There is a one in 200 chance (0.5%) per year of an eruption occurring along the chain. An eruption in the foreseeable future is probably more likely along the Mono–Inyo chain than an unrelated eruption inside Long Valley Caldera. A wide range of effects are expected from future eruptions along

9460-411: The plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on

9570-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases

9680-423: The rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along a fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy

9790-609: The route will be more impacted than ridges but flows and surges could overtop some ridges. Eruptions near snowpacks may produce lahars of mud and ash that devastate valleys and watersheds. Steam blast eruptions under a lake could form large waves capable of flooding nearby areas and starting mudflows. Basalt lava flows may extend more than 31 miles (50 km) from their vent. Dacite and rhyolite lavas produce short, thick flows that rarely extend more than 3.1 miles (5 km) from their vent. Mound-shaped features called lava domes are often created from these flows. Rock fragments thrown from

9900-556: The scenery of the region, and are rendered all the more striking by their proximity to the angular peaks and rugged outlines of the High Sierra." The Mono Basin National Forest Scenic Area , created in 1984, was the first National Scenic Area in the United States. It offers more protection than other United States Forest Service lands, surrounds Mono Lake and its two volcanic islands, Black Point, Panum Crater and much of

10010-540: The southernmost part of the Mono–Inyo Craters volcanic chain. The Mono–Inyo Craters are in the Central Basin and Range ecoregion of the North American Desert . The desert environment of Mono Basin receives about 14 inches (36 cm) of precipitation a year. Annual precipitation around Mammoth Lakes, which is close to the Inyo volcanic chain, is about 23 inches (58 cm). Moisture travels over

10120-404: The strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of the fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of

10230-416: The stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in the fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form

10340-423: The surface of the Mono Craters is barren but its slopes are covered by Jeffrey pine forest and partial greenery. Pumice Valley, directly to the west, is covered by sagebrush scrubland. The soil consists primarily of deep pumice, which does not hold water well. Mycorrhizal fungi in the soil invade the roots of Jeffrey pine trees in a symbiotic relationship that helps the pine absorb water and provides nutrients to

10450-400: The surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in a manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along

10560-442: The surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However, the term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and

10670-507: 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

10780-471: 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

10890-579: The time. Grain size and thickness of tephra generally decreases gradually with distance from a vent. Volcanic ash will likely contaminate air routes east of the vent. Severe damage from super-heated flows of gas, ash and pulverized rock ( pyroclastic flows and surges) may occur at least 9.3 miles (15 km) from an explosive eruption. The amount of damage depends on vent location, topography, and volume of magma erupted. Pyroclastic flows from vents on Mammoth Mountain or other high vent could travel farther by gaining extra momentum from their descent. Valleys along

11000-460: The tunnel on its way to the Los Angeles Aqueduct system. The chain of craters has been the subject of several writers and naturalists. Mark Twain visited Mono Basin in the 1860s and wrote about Mono Lake, but did not mention any of the Mono–Inyo Craters except for the lake's two volcanic islands. He wrote in Roughing It (1872) that the lake was in a "lifeless, hideous desert ..." that was

11110-404: 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

11220-636: The vents to form several steep-sided domes, including Panum Dome and the much larger North Coulee flow. The youngest domes and coulees are 600 to 700 years old and are, therefore, the youngest mountains in North America. The Inyo volcanic chain formed approximately 600 years ago. This activity occurred just a few years after the Mono Crater eruptions, and was caused by a dike of similar composition. The dike eventually became 6.8 miles (11 km) long and up to 33 feet (10 m) wide. The ground above

11330-582: The vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess

11440-401: 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

11550-418: The waters were once mingled with fire." Muir described the Mono Craters as "... heaps of loose ashes that have never been blest by either rain or snow ..." In the spring of 1881 and the fall of 1882, geologist Israel Russell studied the area as a side-trip during his field research of Lake Lahontan , a now dry lake that covered much of nearby Nevada during the last glacial period . His Quaternary History of

11660-492: The west moat of Long Valley Caldera were the first activity associated with the Mono–Inyo Craters system. Eruptions around 300,000 years ago filled the west moat with 800 feet (240 m) of basaltic lava. Basaltic and andesitic eruptive activity then moved to Mono Basin and lasted from 40,000 to 13,000 years ago. Seismic data indicate that a magma chamber with an estimated volume of 48 to 144 cubic miles (200 to 600 km) exists 5.0 to 6.2 miles (8 to 10 km) directly below

11770-442: 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

11880-477: 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

11990-460: 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

12100-546: 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

#554445