The rim or edge of an impact crater is the part that extends above the height of the local surface in a circular or elliptical pattern. In a more specific sense, the rim may refer to the circular or elliptical edge that represents the uppermost tip of this raised portion. If there is no raised portion, the rim refers to the inside edge of the curve where the flat surface meets the curve of the crater bottom. Smaller, simple craters retain rim geometries similar to the features of many craters found on the Moon and the planet Mercury. Large craters are those with a diameter greater than 2.3 km, are distinguished by central uplifts within the impact zone. These larger craters can form rims up to several hundred meters in height. A process to consider when determining the exact height of a crater rim is that melt may have been pushed over the crest of the initial rim from the initial impact, thereby increasing its overall height; when combined with potential weathering due to atmospheric erosion over time, determining the average height of a crater rim can be somewhat difficult.
It has been observed that the slope along the excavated interior of many craters can facilitate a spur-and-gully morphology, including mass wasting events occurring due to slope instability and nearby seismic activity. Complex crater rims observed on Earth have anywhere between 5X – 8X greater height:diameter ratio compared to those observed on the Moon, which can be attributed to the greater force of gravitational acceleration between the two planetary bodies that collide. Additionally, crater depth and the volume of melt produced in the impact are directly related to the gravitational acceleration between the two bodies, it has been proposed that “reverse faulting and thrusting at the final crater rim one of the main contributing factors forming the elevated crater rim”. When an impact crater is formed on a sloped surface, the rim will form in an asymmetric profile; as the impacted surface’s angle of repose increases, the crater’s profile becomes more elongate. The rim type classifications are full-rim craters, broken-rim craters, depressions
South Africa the Republic of South Africa, is the southernmost country in Africa. It is bounded to the south by 2,798 kilometres of coastline of Southern Africa stretching along the South Atlantic and Indian Oceans. South Africa is the largest country in Southern Africa and the 25th-largest country in the world by land area and, with over 57 million people, is the world's 24th-most populous nation, it is the southernmost country on the mainland of the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different African languages, nine of which have official status; the remaining population consists of Africa's largest communities of European and multiracial ancestry. South Africa is a multiethnic society encompassing a wide variety of cultures and religions, its pluralistic makeup is reflected in the constitution's recognition of 11 official languages, the fourth highest number in the world. Two of these languages are of European origin: Afrikaans developed from Dutch and serves as the first language of most coloured and white South Africans.
The country is one of the few in Africa never to have had a coup d'état, regular elections have been held for a century. However, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a large role in the country's recent history and politics; the National Party imposed apartheid in 1948. After a long and sometimes violent struggle by the African National Congress and other anti-apartheid activists both inside and outside the country, the repeal of discriminatory laws began in 1990. Since 1994, all ethnic and linguistic groups have held political representation in the country's liberal democracy, which comprises a parliamentary republic and nine provinces. South Africa is referred to as the "rainbow nation" to describe the country's multicultural diversity in the wake of apartheid; the World Bank classifies South Africa as an upper-middle-income economy, a newly industrialised country.
Its economy is the second-largest in Africa, the 34th-largest in the world. In terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa; however and inequality remain widespread, with about a quarter of the population unemployed and living on less than US$1.25 a day. South Africa has been identified as a middle power in international affairs, maintains significant regional influence; the name "South Africa" is derived from the country's geographic location at the southern tip of Africa. Upon formation, the country was named the Union of South Africa in English, reflecting its origin from the unification of four separate British colonies. Since 1961, the long form name in English has been the "Republic of South Africa". In Dutch, the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika. Since 1994, the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning "south", is a colloquial name for South Africa, while some Pan-Africanist political parties prefer the term "Azania".
South Africa contains human-fossil sites in the world. Archaeologists have recovered extensive fossil remains from a series of caves in Gauteng Province; the area, a UNESCO World Heritage site, has been branded "the Cradle of Humankind". The sites include one of the richest sites for hominin fossils in the world. Other sites include Gondolin Cave Kromdraai, Coopers Cave and Malapa. Raymond Dart identified the first hominin fossil discovered in Africa, the Taung Child in 1924. Further hominin remains have come from the sites of Makapansgat in Limpopo Province and Florisbad in the Free State Province, Border Cave in KwaZulu-Natal Province, Klasies River Mouth in Eastern Cape Province and Pinnacle Point and Die Kelders Cave in Western Cape Province; these finds suggest that various hominid species existed in South Africa from about three million years ago, starting with Australopithecus africanus. There followed species including Australopithecus sediba, Homo ergaster, Homo erectus, Homo rhodesiensis, Homo helmei, Homo naledi and modern humans.
Modern humans have inhabited Southern Africa for at least 170,000 years. Various researchers have located pebble tools within the Vaal River valley. Settlements of Bantu-speaking peoples, who were iron-using agriculturists and herdsmen, were present south of the Limpopo River by the 4th or 5th century CE, they displaced and absorbed the original Khoisan speakers, the Khoikhoi and San peoples. The Bantu moved south; the earliest ironworks in modern-day KwaZulu-Natal Province are believed to date from around 1050. The southernmost group was the Xhosa people, whose language incorporates certain linguistic traits from the earlier Khoisan people; the Xhosa reached the Great Fish River, in today's Eastern Cape Province. As they migrated, these larger Iron Age populations
Algeria the People's Democratic Republic of Algeria, is a country in the Maghreb region of North Africa. The capital and most populous city is Algiers, located in the far north of the country on the Mediterranean coast. With an area of 2,381,741 square kilometres, Algeria is the tenth-largest country in the world, the world's largest Arab country, the largest in Africa. Algeria is bordered to the northeast by Tunisia, to the east by Libya, to the west by Morocco, to the southwest by the Western Saharan territory and Mali, to the southeast by Niger, to the north by the Mediterranean Sea; the country is a semi-presidential republic consisting of 1,541 communes. It has the highest human development index of all non-island African countries. Ancient Algeria has known many empires and dynasties, including ancient Numidians, Carthaginians, Vandals, Umayyads, Idrisid, Rustamid, Zirid, Almoravids, Spaniards and the French colonial empire. Berbers are the indigenous inhabitants of Algeria. Algeria is a middle power.
It supplies large amounts of natural gas to Europe, energy exports are the backbone of the economy. According to OPEC Algeria has the 16th largest oil reserves in the world and the second largest in Africa, while it has the 9th largest reserves of natural gas. Sonatrach, the national oil company, is the largest company in Africa. Algeria has one of the largest defence budget on the continent. Algeria is a member of the African Union, the Arab League, OPEC, the United Nations and is a founding member of the Arab Maghreb Union. On 2 April 2019, president Abdelaziz Bouteflika resigned after nearly 20 years in power, following pressure from the country’s army after mass protests against Bouteflika's campaign for a fifth term; the country's name derives from the city of Algiers. The city's name in turn derives from the Arabic al-Jazā'ir, a truncated form of the older Jazā'ir Banī Mazghanna, employed by medieval geographers such as al-Idrisi. In the region of Ain Hanech, early remnants of hominid occupation in North Africa were found.
Neanderthal tool makers produced hand axes in the Levalloisian and Mousterian styles similar to those in the Levant. Algeria was the site of the highest state of development of Middle Paleolithic Flake tool techniques. Tools of this era, starting about 30,000 BC, are called Aterian; the earliest blade industries in North Africa are called Iberomaurusian. This industry appears to have spread throughout the coastal regions of the Maghreb between 15,000 and 10,000 BC. Neolithic civilization developed in the Saharan and Mediterranean Maghreb as early as 11,000 BC or as late as between 6000 and 2000 BC; this life, richly depicted in the Tassili n'Ajjer paintings, predominated in Algeria until the classical period. The mixture of peoples of North Africa coalesced into a distinct native population that came to be called Berbers, who are the indigenous peoples of northern Africa. From their principal center of power at Carthage, the Carthaginians expanded and established small settlements along the North African coast.
These settlements served as market towns as well as anchorages. As Carthaginian power grew, its impact on the indigenous population increased dramatically. Berber civilization was at a stage in which agriculture, manufacturing and political organization supported several states. Trade links between Carthage and the Berbers in the interior grew, but territorial expansion resulted in the enslavement or military recruitment of some Berbers and in the extraction of tribute from others. By the early 4th century BC, Berbers formed the single largest element of the Carthaginian army. In the Revolt of the Mercenaries, Berber soldiers rebelled from 241 to 238 BC after being unpaid following the defeat of Carthage in the First Punic War, they succeeded in obtaining control of much of Carthage's North African territory, they minted coins bearing the name Libyan, used in Greek to describe natives of North Africa. The Carthaginian state declined because of successive defeats by the Romans in the Punic Wars.
In 146 BC the city of Carthage was destroyed. As Carthaginian power waned, the influence of Berber leaders in the hinterland grew. By the 2nd century BC, several large but loosely administered Berber kingdoms had emerged. Two of them were established behind the coastal areas controlled by Carthage. West of Numidia lay Mauretania, which extended across the Moulouya River in modern-day Morocco to the Atlantic Ocean; the high point of Berber civilization, unequaled until the coming of the Almohads and Almoravids more than a millennium was reached during the reign of Masinissa in the 2nd century BC. After Masinissa's death in 148 BC, the Berber kingdoms were reunited several times. Masinissa's line survived until 24 AD, when the remaining Berber territory was annexed to the Roman Empire. For several centuries Algeria was ruled by the Romans. Like the rest of No
Ouarkziz is a meteorite impact crater in Algeria. It is 3.5 kilometers in diameter and the age is estimated to be less than 70 million years. The crater is exposed at the surface; the Ouarkziz Impact Crater is located in northwestern Algeria, close to the border with Morocco. The crater was formed by a meteor impact less than 70 million years ago, during the late Cretaceous Period of the Mesozoic Era. Called Tindouf, the 3.5-kilometer wide crater has been eroded since its formation. From the vantage point of an astronaut on the International Space Station, the impact crater is visible with a magnifying camera lens. A geologist interpreting this image to build a geological history of the region would conclude that the Ouarkziz crater is younger than the sedimentary rocks, as the rock layers had to be present for the meteor to hit them. A stream channel is visible cutting across the center of the structure, indicating that the channel formed after the impact had occurred; this Principal of Cross-Cutting Relationships attributed to the 19th century geologist Charles Lyell, is a basic logic tool used by geologists to build relative sequence and history of events when investigating a region.
List of impact craters in Africa Fabre, J. Kazi-Tani, N. and Megartsi,M. The "circle" of Ouarkziz, an astrobleme?. Comptes Rendus, Academie des Sciences, Paris, v. 270, serie D, pp. 1212-1215. 1970 Koeberl, C. African meteorite impact craters: Characteristics and geological importance. Journal of African Sciences, v. 18, pp. 263-295. 1994 Lambert, P. McHone, J. F. Jr. Dietz, R. S. Briedj, M. and Djender,M. Impact and impact-like structures in Algeria. Part II, multi-ringed structures. Meteoritics, v. 16, pp. 203-227. 1981 Ouarkziz Impact Crater at NASA Earth ObservatorySatellite image by NASA
Botswana the Republic of Botswana, is a landlocked country in Southern Africa. The British protectorate of Bechuanaland, Botswana adopted its new name after becoming independent within the Commonwealth on 30 September 1966. Since it has maintained a tradition of stable representative republic, with a consistent record of uninterrupted democratic elections and the best perceived corruption ranking in Africa since at least 1998, it is Africa's oldest continuous democracy. Botswana is topographically flat, with up to 70 percent of its territory being the Kalahari Desert, it is bordered by South Africa to the south and southeast, Namibia to the west and north, Zimbabwe to the northeast. Its border with Zambia to the north near Kazungula is poorly defined but is, at most, a few hundred metres long. A mid-sized country of just over 2 million people, Botswana is one of the most sparsely populated countries in the world. Around 10 percent of the population lives in the capital and largest city, Gaborone.
One of the poorest countries in the world—with a GDP per capita of about US$70 per year in the late 1960s—Botswana has since transformed itself into one of the world's fastest-growing economies. The economy is dominated by mining and tourism. Botswana boasts a GDP per capita of about $18,825 per year as of 2015, one of the highest in Africa, its high gross national income gives the country a high standard of living and the highest Human Development Index of continental Sub-Saharan Africa. Botswana is a member of the African Union, the Southern African Development Community, the Commonwealth of Nations, the United Nations; the country has been among the hardest hit by the HIV/AIDS epidemic. Despite the success in programmes to make treatments available to those infected, to educate the populace in general about how to stop the spread of HIV/AIDS, the number of people with AIDS rose from 290,000 in 2005 to 320,000 in 2013; as of 2014, Botswana has the third-highest prevalence rate for HIV/AIDS, with 20% of the population infected.
The country's name means "land of the tswana", referring to the dominant ethnic group in Botswana. The term Batswana was applied to the Tswana, still the case. However, it has come to be used as a demonym for all citizens of Botswana. Many English dictionaries recommend the term Botswanan to refer to people of Botswana. Archaeological digs have shown. Stone tools and fauna remains have shown that all areas of the country were inhabited at least 400,000 years ago. Evidence left by modern humans such as cave paintings are about 73,000 years old; the original inhabitants of southern Africa were the Khoi peoples. Both speak Khoisan languages and hunted and traded over long distances; when cattle were first introduced about 2000 years ago into southern Africa, pastoralism became a major feature of the economy, since the region had large grasslands free of tsetse fly. It is unclear when Bantu-speaking peoples first moved into the country from the north, although AD 600 seems to be a consensus estimate.
In that era, the ancestors of the modern-day Kalanga moved into what is now the north-eastern areas of the country. These proto-Kalanga were connected to states in Zimbabwe as well as to the Mapungubwe state; these states, located outside of current Botswana's borders, appear to have kept massive cattle herds in what is now the Central District—apparently at numbers approaching modern cattle density. This massive cattle-raising complex prospered until 1300 AD or so, seems to have regressed following the collapse of Mapungubwe. During this era, the first Tswana-speaking groups, the Bakgalagadi, moved into the southern areas of the Kalahari. All these various peoples were connected to trade routes that ran via the Limpopo River to the Indian Ocean, trade goods from Asia such as beads made their way to Botswana most in exchange for ivory and rhinoceros horn; the arrival of the ancestors of the Tswana-speakers who came to control the region has yet to be dated precisely. Members of the Bakwena, a chieftaincy under a legendary leader named Kgabo II, made their way into the southern Kalahari by AD 1500, at the latest, his people drove the Bakgalagadi inhabitants west into the desert.
Over the years, several offshoots of the Bakwena moved into adjoining territories. The Bangwaketse occupied areas to the west, while the Bangwato moved northeast into Kalanga areas. Not long afterwards, a Bangwato offshoot known as the Batawana migrated into the Okavango Delta in the 1790s; the first written records relating to modern-day Botswana appear in 1824. What these records show is that the Bangwaketse had become the predominant power in the region. Under the rule of Makaba II, the Bangwaketse kept vast herds of cattle in well-protected desert areas, used their military prowess to raid their neighbors. Other chiefdoms in the area, by this time, had capitals of 10,000 or so and were prosperous; this equilibrium came to end during the Mfecane period, 1823–1843, when a succession of invading peoples from South Africa entered the country. Although the Bangwaketse were able to defeat the invading Bakololo in 1826, over time all the major chiefdoms in Botswana were attacked and impoverished.
The Bakololo and Amandebele raided and took large numbers of cattle and children from the Batswana—most of whom were driven into the desert or sanctuary areas such as hilltops and caves. Only after 1843, when the Amandebele moved into western Zimbabwe, did this threat subside. During th
Roter Kamm crater
Roter Kamm is a meteorite crater, located in the Sperrgebiet, within the Namibian section of the Namib Desert 80 kilometres north of Oranjemund and 12 kilometres southwest of Aurus Mountain in the ǁKaras Region. The crater is 130 metres deep; the age is estimated at 4.81 ± 0.5 Ma. The crater is exposed at the surface, but its original floor is covered by sand deposits at least 100 metres thick; the meteorite hit a layer of Precambrian granitic gneiss, part of the Namaqua Metamorphic Complex, overlaid with some younger sedimentary rocks. No parts of the meteorite have been found, suggesting that it evaporated upon impact; the meteor that hit it was the size of an SUV. The Roter Kamm impact structure exposes a large volume of cataclastic/mylonitic and pseudotachylitic breccias in the basement granite and gneisses, unusual for small craters. Anomalous quartz found at the rim of the crater, the primary fluid inclusions in the quartz, seem to provide evidence for post-impact hydrothermal activity, generated by impact heat, at the Roter Kamm impact crater.
Eolian and alluvial processes each played a role in modifying the Roter Kamm impact crater since its formation. Much of the more recent history of crater modification relates to eolian processes. Active mobile sands bury the crater and mask most of the signatures associated with prior activity by other processes. Ongoing eolian erosion is responsible for scouring of the exposed rim. List of impact craters in Africa Geology of Namibia Grant, John A.. 1997. Gradation of the Roter Kamm impact crater, Namibia. Journal of Geophysical Research 102. 16,327–16,338. Accessed 2018-08-25. Hecht, Lutz. 2008. New impact-melt rock from the Roter Kamm impact structure, Namibia: Further constraints on impact age, melt rock chemistry, projectile composition. Meteoritics & Planetary Science 43. 1201–1218. Koeberl, Christian. 1989. Anomalous quartz from the Roter Kamm impact crater, Namibia: Evidence for post-impact hydrothermal activity?. Geochimica et Cosmochimica Acta 53. 2113–2118. Accessed 2018-08-25. Reimold, Wolf Uwe.
1994. Roter Kamm impact crater, Namibia: Geochemistry of basement rocks and breccias. Geochimica et Cosmochimica Acta 58. 2689–2710. Accessed 2018-08-25. Bishop, J. Koeberl, C. and Reimold, W. U. Geochemistry of the Roter Kamm impact crater, SWA/Namibia. Meteoritics, v. 24, p. 252. 1989 Blumberg, D. G. McHone, J. F. Kuzmin, R. and Greeley, R. Radar imaging of impact craters by SIR-C/X-SAR. Lunar and Planetary Science XXVI, pp. 139-140. 1995 Brandt, D. Reimold, W. U. Franzsen, A. J. Koeberl, C. Wendorff, L. Geophysical profile of the Roter Kamm impact crater, Meteoritics & Planetary Science 33, pp. 447-453. 1998 Brandt, D. Reimold, W. U. Wendof, L. Koeberl, C. and Grant, J. Geophysical signatures of the Roter Kamm impact crater, Namibia. Lunar and Planetary Science, v. XXVII, pp. 153-154. 1996 Degenhardt, Jr,J. J. Buchanan, P. C. and Reid, A. M. Impactite and pseudotachylite from Roter Kamm crater, Namibia. International Conference on Large Meteorite Impacts and Planetary Evolution, LPI Contribution No. 790, pp. 20-21.
1992 Degenhardt, Jr, J. J. Buchanan, P. C. Reid, A. M. and Miller, R. McG. Breccia veins and dykes associated with Namibia. Geological Society of America Special Paper 293, pp. 197-208. 1994 Degenhardt, Jr, J. J. Reid, A. M. Buchanan, P. C. and Miller, R. McG. Melt breccias from Namibia. Lunar and Planetary Science XXVI, pp. 323-324. 1995 Degenhardt, Jr, J. J. Reid, A. M. Miller, R. McG. and Reimold, W. U. Breccias resembling melt bombs from the Roter Kamm Crater. Meteorites & Planetary Science, v. 31, pp. 413-415. 1996 Dietz, R. S. Roter Kamm, southwest Africa: Probable meteorite crater. Meteoritics, v. 2, pp. 311-314. 1965 Fudali, R. F. Roter Kamm: Evidence for an impact origin. Meteoritics, v. 8, pp. 245-257. 1973 Grieve, R. A. F. Recent studies at the Roter Kamm impact crater. Meteoritics, v. 28, pp. 160. 1993 Hartung, J. B. Kunk, M. R. Reimold, W. U. Miller, R. McG. and Grieve, R. A. F. Roter Kamm crater age: 3.5 to 4.0 Ma. Meteoritics, v. 26, pp. 342-343. 1991. Koeberl, C. African meteorite impact craters: Characteristics and geological importance.
Journal of African Sciences, v. 18, pp. 263-295. 1994 Koeberl, C. Klein, J. Matsuda, J. Nagao, K. Reimold, W. U. and Storzer, D. Roter Kamm impact crater, Namibia: Age constraints from K-Ar, Rb-Sr, fission track, 10Be-26 Al studies. Meteoritics, v. 27, 244-245. 1992 Koeberl, C. Reimold, W. U. Bishop, J. and Miller, R. McG. Roter Kamm impact crater, SWA/Namibia: New geochemical and isotopic studies and further evidence for post-impact hydrothermal activity. Lunar and Planetary Science XXI, pp. 647-648. 1990 Koeberl, C. Reimold, W. U. Gotzinger, M. and Fredriksson, K. Quartz at the Roter Kamm crater and post-impact hydrothermal activity: A reply to E. Roedder. Geochemica et Cosmochimica Acta, v. 54, pp. 3249-3251. 1990 Koeberl, C. The age of the Roter Kamm impact crater, Namibia: Constraints from 40Ar-39Ar, K-Ar, Rb-Sr, fission track, 10Be-26Al studies. Meteoritics, v. 28, pp. 204-212. 1993 Miller, R. McG. Reimold, W. U. Deformation and shock deformation in rocks from the Roter Kamm crater, SWA/Nambia. Meteoritics, v. 21, pp. 456-458.
1986 Miller, R. M. Roter Kamm impact crater of Namibia.
Amguid is a meteorite crater in Algeria. It is 500 to 530 metres in diameter 65 m deep and the age is estimated to be less than 100,000 years and is Pleistocene; the crater is exposed at the surface. Crater was discovered by Europeans in 1948, first scientific description was made by Jean-Phillippe Lefranc in 1969. List of impact craters in Africa Koeberl, C. African meteorite impact craters: Characteristics and geological importance. Journal of African Earth Sciences, v. 18, pp. 263-295. 1994 Lambert, P. McHone, J. F. Jr. Dietz, R. S. and Houfani,M. Impact and impact-like structures in Algeria. Part I. Four bowl-shaped depressions. Meteoritics, v. 15, pp. 157-179. 1980 Lefranc, J. -P. Exploration of a meteorite crater at Amguid. Academie des Sciences, Comptes Rendus, Serie D, v. 268, pp. 900-902. 1969 McHone, J. F. Jr. Lambert, P. Dietz, R. S. and Briedj,M. Impact structures in Algeria. Meteoritics, v. 15, pp. 331-332. 1980 All Africa Magharebia