Fault scarp

An eroded fault scarp from the Gobi Desert of Mongolia (left) and at Borah Peak in Idaho. This fault scarp (white line at the base of the tan hills) was formed in the 1983 Borah Peak earthquake

FaultLineScarp
Borah1983

A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other.[1] It is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old inactive geologic fault (a sort of old rupture), or by a movement on a recent active fault.

Characteristics

Fault scarps often contain highly fractured rock of both hard and weak consistency. In many cases, bluffs form from the upthrown block and can be very steep. The height of the scarp formation is equal to the vertical displacement along the fault. Active scarps are usually formed by tectonic displacement, e.g. when an earthquake changes the elevation of the ground and can be caused by any type of fault, including strike-slip faults, whose motion is primarily horizontal. This movement is usually episodic, with the height of the bluffs being the result of multiple movements over time. Displacement of around 5 to 10 meters per tectonic event is common.[2]

Red Canyon fault scarp sjr00100
This fault scarp was created by the 1959 Hebgen Lake earthquake. Photo taken August 19, 1959.

Due to the dramatic uplift along the fault, the fault scarp is very prone to erosion, especially if the material being uplifted consists of unconsolidated sediment. Weathering, mass wasting, and water runoff can soon wear down these bluffs, sometimes resulting in V-shaped valleys along runoff channels. Adjacent V-shaped valley formations give the remaining fault spurs a very triangular shape. This formation is known as a triangular facet; however, this landform is not limited to fault scarps.

Fault scarps may be only a few centimeters or many meters high. Fault-line scarps are coincident with faults, but are most typically formed by the erosion of weaker rocks that have been brought alongside more resistant ones by the movement along the fault. In the case of old eroded fault scarps, active erosion may have moved the physical cliff back away from the actual fault location which may be buried beneath a talus, alluvial fan or the sediments of the valley fill.

Examples

  • Teton Range

The Teton Range in Wyoming is an example of an active fault scarp. The dramatic topography of the Tetons is due to geologically recent activity on the Teton Fault.[3]

References

  1. ^ Essentials of Geology, 3rd ed., Stephen Marshak
  2. ^ Arthur N Strahler. Physical Geography. New York: John Wiley & Sons, Inc, 1960, second edition, p. 475
  3. ^ Byrd, J.O.D., Smith, R.B., Geissman, J.W. (1994) The Teton fault, Wyoming: Topographic signature, neotectonics, and mechanisms of deformation, Journal of Geophysical Research (99), No. B10, p. 20095-20122

Sources

  • Easterbrook, D. J. (1999) Surface processes and landforms. (Second Ed). Prentice Hall, Upper Saddle River, New Jersey.
Abert

Abert is a surname. Notable people with the surname include:

John James Abert (1788–1863), cartographer

James William Abert (1820–1897), explorer

Johann Joseph Abert (1832–1915), composer

Hermann Abert (1871–1927), music historian

Abert Rim

Abert Rim in Lake County, Oregon is one of the highest fault scarps in the United States. It rises 2,490 feet (760 m) above the valley floor, finishing with a 820-foot (250 m) sheer-sided basalt cap. It was formed during the Miocene epoch. At that time basaltic flood lavas covered much of eastern Oregon. In subsequent faulting, great blocks were tilted and Abert Rim is at the western end of one of these blocks, while Lake Abert lies on top of another. Stretching more than 30 miles (48 km) from Lakeview north to Alkali Lake, Abert Rim is also the longest exposed fault scarp in North America.

Bighorn sheep were transplanted to the rim in 1975 and 1977 from nearby Hart Mountain, and are often spotted from the Abert Rim geologic point of interest sign located along Highway 395. Raptors, such as the Ferruginous Hawk, are also common in the area.

The Chewaucan River enters the lake from the south, however it has no outlet. The lake level varies depending on rainfall and it nearly completely dried up 140 years ago. It is one of the Great Basin lakes.

The escarpment and lake were first mapped on December 20, 1843, by John C. Frémont, who named it after Colonel John James Abert, his commanding officer.The southern section of Abert Rim is a popular spot for hang gliding because of the frequent thermals created by warm valley air rising up against the cliffs. The area is considered by many to be the hang gliding capital of the West. National hang gliding festivals are held each year in late June and during the Fourth of July.

Coastal Cliff of northern Chile

The Coastal Cliff of northern Chile (Spanish: Acantilado Costero) stretches over a length of more than 1000 km along the Atacama Desert. It makes up a large part of the western boundary to the Chilean Coast Range in the regions of Tarapacá and Antofagasta, and Atacama. According to Roland Paskoff the modern cliff origined from a scarp retreat of a fault scarp, thus at present the cliff does not follow any fault.In some locations a series of coastal benches can be found below the cliff. Despite alternating uplift and subsidence of the continent at a decadal timescale the cliff and the whole western edge of the South American plate has faced a long-term uplift during the last 2.5 million years.

Edgar Dam

The Edgar Dam is an earthfill embankment saddle dam without a spillway, located offstream in the South West region of Tasmania, Australia.

The impounded reservoir, also formed with the Scotts Peak Dam and the Serpentine Dam, is called Lake Pedder which flooded Lake Edgar, a naturally forming fault scarp pond. The dam was constructed in 1973 by the Hydro Electric Corporation (TAS) as part of the Gordon River Power Development Scheme for the purpose of generating hydro-electric power via the Gordon Power Station. Water from Lake Pedder is diverted to Lake Gordon (formed by the Gordon Dam) via the McPartlan Pass Canal.

Elgeyo Escarpment

Elgeyo escarpment is a fault-scarp caused by post-Miocene faulting. Miocene beds are still visible. The escarpment is part of the western wall of the Great Rift Valley.

The northwest part of Kenya has three main geographic zones running in parallel north to south. There is the highland plateau, which rises gradually to 3,350 meters above sea level, on the Cherangani Hills. In the intermediate zone is the Elgeyo Escarpment which rapidly gives way to the lower Kerio Valley. The yearly rainfall in the escarpment area ranges between 100–140 cm.

La Macarena Fault

The La Macarena Fault (Spanish: Falla de La Macarena) is a thrust fault in the department of Meta in Colombia. The fault has a total length of 50.3 kilometres (31.3 mi) and runs along an average north to south strike of 000.6 ± 9 along the east side of the Serranía de la Macarena.

Lake Edgar

Lake Edgar was a natural fault scarp pond on the upper reaches of the Huon River in South West Tasmania.

Llecué

Llecué is a mountain in the commune of Los Lagos in Los Ríos Region, southern Chile. The mountain lies west of mount Tralcán and immediately south of San Pedro River. The eastern slope of the mountain is a sharp fault scarp as is part of its western slope. The name of the mountain is Mapuche based on llecu, meaning near, and hue, meaning place. The mountain lies next to the catastrophic landslide of 1575 which dammed San Pedro River causing a flood when the dam burst.

Lost River Range

The Lost River Range is a high mountain range of the Rocky Mountains, located in central Idaho, in the northwestern United States.It runs southeast for approximately 75 miles (121 km) from the Salmon River near the community of Challis to the Snake River Valley near Arco. To the west are the valleys of the Salmon and the Big Lost Rivers, while to the east are the Little Lost River and Pashimeroi Valleys.

The range starts at the east bank of the Salmon River, at an elevation of about 5,000 feet (1,500 m). It quickly rises to Grouse Creek Mountain (11,085 ft, 3,378 m) and Dickey Peak (11,141 ft, 3,395 m), and then descends to Double Springs Pass, location of one of just two roads to cross the range. Nearby is an interpretive site explaining the effects of the magnitude 6.9 Borah Peak earthquake that hit the range on October 28, 1983. The Big Lost River Valley fell and the Lost River Range rose, leaving a fault scarp of up to 14 ft (4.3 m) along the base of the mountains.

The range then rises into its high central section, which includes many of the state's highest peaks. Borah Peak, the highest, climbs to 12,662 ft (3,859 m). Further south are Mount Idaho (12,065 ft, 3,677 m), Leatherman Peak (12,228 ft, 3,727 m), Mount Church (over 12,200 ft, 3,720 m), Mount Breitenbach (12,140 ft, 3,700 m), and Lost River Mountain (12,078 ft, 3,681 m). To the east of this section of the range lie the remote canyons of the Upper Pashimeroi Valley, including scenic Merriam Lake.

The range then descends to Pass Creek Summit, the second road to cross its crest. It continues to King Mountain (10,612 ft, 3,235 m), a favorite site for hang gliders. Finally it descends sharply to the Snake River Valley near the community of Arco, at an elevation of 5,300 ft (1,600 m).

Mau Escarpment

The Mau Escarpment is a fault scarp running along the western edge of the Great Rift Valley in Kenya. The top of the escarpment reaches approximately 3000 m (10,000 ft) above sea level, and is over 1000 m higher than the floor of the Rift Valley.

Meers Fault

Meers Fault is a fault in Oklahoma that extends from Kiowa County to Comanche County. It is marked by a 22–26 kilometers (14–16 mi) long conspicuous fault scarp but the fault extends beyond the ends of this scarp. The Meers fault is part of a group of faults that lie between the Anadarko Basin and the Wichita Mountains.

While the fault was active during the Permian-Cambrian, movement possibly accompanied by earthquakes took place during the Holocene and formed the fault scarp, with one earthquake occurring less than 2,000 years ago. There is currently no seismicity on the fault but it is considered an earthquake hazard.

Nuʻuanu Slide

Nuʻuanu Slide or Nuʻuanu Debris Avalanche is the largest of seventeen submarine landslides around the Hawaiian Islands and at 200 km in length, one of the largest landslides on Earth. It broke from the eastern or windward side of Oahu, Hawaii between 1 to 1.5 million years ago and lies in the Pacific Ocean north of Molokai.At the time of collapse, Oahu was part of the conglomerate island Maui Nui, elevated above the ocean from lower sea levels, and contained the Koʻolau Volcano. The eastern half of the mountain collapsed nearly in half at the caldera. The remains of the eastern half of the caldera is now Kāneʻohe Bay and the new western side is the Koʻolau Range above the bay, including observation point Nuʻuanu Pali. Though the remaining ridge appears to be a steep and weathered fault scarp evidence suggests the geographic features are from wind and water rather than the landslide event.The volcano collapsed nearly in half at the caldera with the eastern half falling into the ocean cataclysmically with enough force to send debris including the massive Tuscaloosa seamount across the ocean floor and up a ridge.

Scotts Peak Dam

The Scotts Peak Dam is a rockfill embankment dam without a spillway across the Huon River, located in the South West region of Tasmania, Australia.

The impounded reservoir, also formed with the Edgar Dam and the Serpentine Dam, is called Lake Pedder which flooded Lake Edgar, a naturally forming fault scarp pond. The dam was constructed in 1973 by the Hydro Electric Corporation (TAS) as part of the Gordon River Power Development Scheme for the purpose of generating hydro-electric power via the conventional Gordon Power Station. Water from Lake Pedder is diverted to Lake Gordon (formed by the Gordon Dam) via the McPartlan Pass Canal.

Serpentine Dam (Tasmania)

The Serpentine Dam is a rockfill embankment dam with a concrete face and a controlled spillway across the Serpentine River, located in the South West region of Tasmania, Australia.

The impounded reservoir, also formed with the Edgar Dam and the Scotts Peak Dam, is called Lake Pedder which flooded Lake Edgar, a naturally forming fault scarp pond. The dam was constructed in 1971 by the Hydro Electric Corporation (TAS) as part of the Gordon River Power Development Scheme for the purpose of generating hydro-electric power via the conventional Gordon Power Station. Water from Lake Pedder is diverted to Lake Gordon (formed by the Gordon Dam) via the McPartlan Pass Canal.

Sierra Madre Fault Zone

Situated at the boundary to the San Gabriel Valley and San Fernando Valley, the Sierra Madre Fault Zone (also known as the Sierra Madre-Cucamonga Fault) runs along the southern edge of the San Gabriel Mountains for a total of 95 kilometers (59 mi), where the northwesternmost 19 km (12 mi) comprises the San Fernando Fault (the section responsible for the 1971 San Fernando earthquake). A 1980s paleoseismic study that included a trench investigation and mapping revealed that a major earthquake had most likely not occurred to the east of the San Fernando rupture area for at least the last several thousand, and possibly the last 11,000 years.The 1971 event was the first in a series (1987 Whittier Narrows, 1991 Sierra Madre, 1994 Northridge) of damaging earthquakes which have occurred on reverse faults in the Los Angeles area. The events triggered discussions concerning the largest magnitude earthquake that could be generated by one of the faults, especially in the Transverse Ranges, but the focal point of earthquake hazard assessments in California are often the San Andreas Fault and other associated dextral faults. Although there is a lack of paleoseismic data on reverse faults in the Los Angeles area, a trench excavation at a site on the Sierra Madre-Cucamonga Fault revealed that two large historic earthquakes occurred in the last 15,000 years.

The fault was studied again in the late 1990s in the Loma Alta Park near Millard Canyon where a fault scarp larger than 2 m (6 ft 7 in) was accessible along a (late quaternary) elevated stream terrace. The clearly defined fault was exposed in the trench and emerged as a .5 m (1 ft 8 in) band of coarse gravels lining the hanging wall. By studying the truncated rocks and a wedge-shaped accumulation of gravel and soil, it was possible to visually reconstruct the original geometry of the rock prior to the thrust and eventual and partial collapse of the hanging wall back onto the footwall. An estimate for the maximum slip of the event was given as 3.8–4 meters (12–13 ft).

The evidence found at the Loma Alta trench investigation site brought new information into the deliberation regarding the maximum size of earthquakes near Los Angeles. The large amount of slip observed there did not correspond with a short 15–20 km (9.3–12.4 mi) rupture length of the Sierra Madre Fault Zone, and instead suggested that the historical thrust earthquakes were much larger in magnitude than what was seen with the 1971 event, given its smaller 2 meters (6 ft 7 in) of maximum observed displacement. Two methods were employed to infer the scope of the events at the site (one regression-based and the other based on the seismic moment) and produced a maximum magnitude of 7.5 or 7.6 for the most recent movement of the fault. The results supported an earlier hypothesis that seismic energy release on the Sierra Madre Fault Zone is characterized by infrequent but large earthquakes. A duplicate event in modern times would rupture to the south towards populated areas and would produce strong ground motion capable of damaging modern buildings and other critical infrastructure.

Troltrolhue

Troltrolhue or Cordillera Troltrolhue is a mountain and mountain range in Los Ríos Region, southern Chile. The mountain range runs from west to east across five communes; Mariquina, Lanco, Máfil, Los Lagos and Panguipulli. It lies south and east of Cruces River and west of Calafquén and Panguipulli lakes. Part of the southeastern slope of the mountain range is a fault scarp. There are historical placer-type gold mines in the Troltrolhue.

Usangu Plain

The Usangu Plain is a lowland in south-central Tanzania. It is named for the Sangu people.

Yanar Dag

Yanar Dag (Azerbaijani: Yanar Dağ, meaning "burning mountain") is a natural gas fire which blazes continuously on a hillside on the Absheron Peninsula on the Caspian Sea near Baku, the capital of Azerbaijan (a country which itself is known as "the Land of Fire"). Flames jet into the air 3 metres (9.8 ft) from a thin, porous sandstone layer. Administratively, Yanar Dag belongs to Absheron District of Azerbaijan.

Unlike mud volcanoes, the Yanar Dag flame burns fairly steadily, as it involves a steady seep of gas from the subsurface. It is claimed that the Yanar Dag flame was only noted when accidentally lit by a shepherd in the 1950s. There is no seepage of mud or liquid, which distinguishes it from the nearby mud volcanoes of Lökbatan or Gobustan.

On the territory of Yanar Dag, State Historical-Cultural and Natural Reserve was established by the Presidential decree dated 2 May 2007 which operates under the control of State Tourism Agency of Azerbaijan. After major overhaul between 2017-2019, Yanardag Museum and Yanardag Cromlech Stone Exhibition were launched in the area of the Reserve.

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