35-548: Ostriches are large flightless birds . Two living species are recognised, the common ostrich , native to large areas of sub-Saharan Africa , and the Somali ostrich , native to the Horn of Africa . They are the heaviest and largest living birds, with adult common ostriches weighing anywhere between 63.5 and 145 kilograms and laying the largest eggs of any living land animal. With the ability to run at 70 km/h (43.5 mph), they are
70-633: A number of active and dormant volcanoes, among them: Mount Kilimanjaro , Mount Kenya , Mount Longonot , Menengai Crater, Mount Karisimbi , Mount Nyiragongo , Mount Meru and Mount Elgon , as well as the Crater Highlands in Tanzania. Although most of these mountains lie outside of the rift valley, the EAR created them. Notable active examples of EAR volcanism include Erta Ale , Dalaffilla (also called Gabuli, Alu-Dalafilla), and Ol Doinyo Lengai . Erta Ale
105-779: Is a basaltic shield volcano in the Afar Region of northeastern Ethiopia, active continuously since at least 1967, with a summit lava lake documented since at least 1906. The 2008 eruption of Dalafilla, its only documented activity since the start of the Holocene , is the largest recorded eruption in Ethiopian history. Ol Doinyo Lengai is currently the only active natrocarbonatite volcano on Earth. Its magma contains almost no silica; typical lava flows have viscosities of less than 100 Pa⋅s, comparable to olive oil at 26 °C (79 °F). EAR-related volcanic structures with dated activity since
140-570: Is an active continental rift zone in East Africa . The EAR began developing around the onset of the Miocene , 22–25 million years ago. It was formerly considered to be part of a larger Great Rift Valley that extended north to Asia Minor . A narrow zone, the rift is a developing divergent tectonic plate boundary where the African plate is in the process of splitting into two tectonic plates, called
175-544: Is another product that is made using ostrich fat. Ostriches are of the genus Struthio in the order Struthioniformes , part of the infra-class Palaeognathae , a diverse group of flightless birds also known as ratites that includes the emus , rheas , cassowaries , kiwis and the extinct elephant birds and moas . The common ostrich was historically native to the Arabian Peninsula , and ostriches were present across Asia as far east as China and Mongolia during
210-479: Is constructive to test hypotheses on computer based geodynamical models. A 3D numerical geodynamic model of the plume-crust coupling was capable of reproducing the lateral asymmetry of the EAR around the Tanzania craton . Numerical modeling of plume-induced continental break-up shows two distinct stages, crustal rifting followed by lithospheric breakup, and the upwelling between stages of an upper mantle plume. Prior to
245-569: Is contentious and in need of revision pending more good material. The species are: Flightless Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.226 via cp1108 cp1108, Varnish XID 762611861 Upstream caches: cp1108 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 05:33:06 GMT East African Rift The East African Rift ( EAR ) or East African Rift System ( EARS )
280-542: The Ethiopian Highlands and the Kenya Highlands are hotspots of higher rainfall amid the semi-arid to arid lowlands of East Africa. Lakes which form within the rift, including Lake Victoria , have a large effect on regional climate. They are a source of water vapour, and also lead to the formation of lake breeze systems , which affect weather across large areas of East Africa. The east to west river valleys within
315-493: The Late Pleistocene and possibly into the Holocene . The genus Struthio was first described by Carl Linnaeus in 1758. The genus was used by Linnaeus and other early taxonomists to include the emu , rhea , and cassowary , until they each were placed in their own genera. The Somali ostrich ( Struthio molybdophanes ) has recently become recognized as a separate species by most authorities, while others are still reviewing
350-626: The Main Ethiopian Rift , runs southward from the Afar triple junction, and continues south as the Kenyan Rift Valley, then transects Congo DR , Uganda , Rwanda , Burundi , Zambia , Tanzania , Malawi and Mozambique . The Western Rift Valley includes the Albertine Rift , and farther south, the valley of Lake Malawi . The rift also continues offshore from the coast of Mozambique along
385-627: The Oligocene , with the majority of the volcanism coinciding with the opening of the Red Sea and the Gulf of Aden approximately 30 Ma. The composition of the volcanics are a continuum of ultra-alkaline to tholeiitic and felsic rocks. It has been suggested that the diversity of the compositions could be partially explained by different mantle source regions. The EAR also cuts through old sedimentary rocks deposited in ancient basins. The East African Rift Zone includes
SECTION 10
#1732858386012420-626: The Somali plate and the Nubian plate , at a rate of 6–7 mm (0.24–0.28 in) per year. The rift system consists of three microplates, the Victoria microplate to the north, and the Rovuma and Lwandle microplates to the south. The Victoria microplate is rotating anti-clockwise with respect to the African plate. Its rotation is caused by the configuration of mechanically weaker and stronger lithospheric regions in
455-399: The lithosphere in saturated areas, making the thinning lithosphere behave like a mid-ocean ridge . According to marine geologist Kathleen Crane , the rift could eventually cause eastern Africa to separate from the mainland, although this potential event could take tens of millions of years. Studies that contribute to the broader understanding on the evolution of rifts can be grouped into
490-488: The African fossil species is comparatively straightforward, many Asian species of ostrich have been described from fragmentary remains, and their interrelationships and how they relate to the African ostriches are confusing. In India, Mongolia and China , ostriches are known to have become extinct only around, or even after, the end of the last ice age ; images of ostriches have been found prehistoric Chinese pottery and petroglyphs . Today, ostriches are only found natively in
525-404: The EAR. The results corroborate the coexistence of a superplume "common to the entire rift" with another mantle material source being either of subcontinental type or of mid-ocean ridge type. The geophysical method of seismic tomography is a suitable tool to investigate Earth's subsurface structures deeper than the crust. It is an inverse problem technique that models which are the velocities of
560-896: The EARS. Many of the African Great Lakes lie within the Rift Valley. A series of distinct rift basins, the East African Rift System extends over thousands of kilometers. North of the Afar triple junction, the rift follows two paths: west to the Red Sea Rift and east to the Aden Ridge in the Gulf of Aden . Southward from the Afar triple junction , the EAR consists of two main branches. The Eastern Rift Valley (also known as Gregory Rift ) includes
595-585: The Kerimba and Lacerda grabens , which are joined by the Davie Ridge, a 2,200 km-long (1,400 mi) relic fracture zone that cuts across the West Somali basin, straddling the boundary between Tanzania and Mozambique. The Davie Ridge ranges between 30–120 km (19–75 mi) wide, with a west-facing scarp (east-plunging arch) along the southern half of its length that rises to 2,300 m (7,500 ft) above
630-595: The Somali Jet) in the western Indian Ocean . The Somali Jet supplies water vapour for the high rainfall during the Indian Monsoon and is responsible for roughly half the global cross-equatorial atmospheric mass flux in the lower-branch of Hadley Circulation . The Rift Valley in East Africa has been a rich source of hominid fossils that allow the study of human evolution. The rapidly eroding highlands quickly filled
665-623: The Somali ostrich, but they are kept from interbreeding by behavioral and ecological differences. The Arabian ostriches in Asia Minor and Arabia were hunted to extinction by the middle of the 20th century, and in Israel attempts to introduce North African ostriches to fill their ecological role have failed. Escaped common ostriches in Australia have established feral populations. In 2008, S. linxiaensis
700-606: The development of deep asymmetric basins. The second stage of rifting was characterized by the deactivation of large boundary faults, the development of internal fault segments, and the concentration of magmatic activity towards the rifts. Today, the narrow rift segments of the East African Rift system form zones of localized strain. These rifts are the result of the actions of numerous normal faults which are typical of all tectonic rift zones. As aforementioned, voluminous magmatism and continental flood basalts characterize some of
735-563: The effects of deep-rooted mantle plumes are an important hypothesis, their location and dynamics are poorly understood, and a matter of active research. The question is still debated. The most recent and accepted view is the theory put forth in 2009: that magmatism and plate tectonics have a feedback with one another, controlled by oblique rifting conditions. According to this theory, lithospheric thinning generates volcanic activity, further increasing magmatic processes such as intrusions and numerous small plumes. These processes further thin
SECTION 20
#1732858386012770-744: The evidence. Struthionidae is a member of the Struthioniformes , a group of paleognath birds which first appeared during the Early Eocene , and includes a variety of flightless forms which were present across the Northern Hemisphere (Europe, Asia and North America) during the Eocene epoch. The closest relatives of Struthionidae within the Struthioniformes are the Ergilornithidae , known from
805-564: The fastest birds on land. They are farmed worldwide, with significant industries in the Philippines and in Namibia . South Africa produces about 70% of global ostrich products, with the industry largely centered around the town of Oudtshoorn . Ostrich leather is a lucrative commodity, and the large feathers are used as plumes for the decoration of ceremonial headgear. Ostrich eggs and meat have been used by humans for millennia. Ostrich oil
840-405: The inner Earth that reproduce the seismographic data recorded all around the world. Recent improvements of tomographic Earth models of P wave and S wave velocities suggest that a superplume upwelling from the lower mantle at the northeastern EAR feeds plumes of smaller scale into the upper mantle . Parallel to geological and geophysical measures (e.g. isotope ratios and seismic velocities) it
875-504: The late Eocene to early Pliocene of Asia. It is therefore most likely that Struthionidae originated in Asia. The earliest fossils of the genus Struthio are from the early Miocene ~21 million years ago of Namibia in Africa, so it is proposed that genus is of African origin. By the middle to late Miocene (5–13 mya) they had spread to and become widespread across Eurasia. While the relationship of
910-650: The onset of the Holocene include approximately 50 in Ethiopia, 17 in Kenya , and 9 in Tanzania . The EAR is the largest seismically active rift system on Earth today. The majority of earthquakes occur near the Afar Depression, with the largest typically occurring along or near major border faults. Seismic events in the past century are estimated to have reached a maximum moment magnitude of 7.0. The seismicity trends parallel to
945-724: The rift segments, while other segments, such as the Western branch, have only very small volumes of volcanic rock. The African continental crust is generally cool and strong. Many cratons are found throughout the EAR, such as the Tanzania and Kaapvaal cratons . The cratons are thick, and have survived for billions of years with little tectonic activity. They are characterized by greenstone belts , tonalites , and other high-grade metamorphic lithologies. The cratons are of significant importance in terms of mineral resources , with major deposits of gold, antimony, iron, chromium and nickel. A large volume of continental flood basalts erupted during
980-673: The rift system, including the Turkana Channel in northern Kenya and the Zambezi river valley, concentrate low-level easterly winds and accelerate them towards Central Africa . This leaves East Africa drier than it otherwise would be, and also supports the high rainfall in the Congo Basin rainforest . The formation of the east–west valleys could in turn be important for the aridification of East Africa over millions of years. The barrier presented by EARS concentrates monsoonal winds (known as
1015-451: The rift system, with a shallow focal depth of 12–15 km (7.5–9.3 mi) beneath the rift axis. Further away from the rift axis, focal depths can be below 30 km (19 mi). Focal mechanism solutions strike NE and frequently demonstrate normal dip-slip faulting, although left-lateral motion is also observed. The East African Rift system affects regional, continental and even global climate. Regions of higher elevation, including
1050-515: The rift's formation, enormous continental flood basalts erupted, uplifting the Ethiopian , Somali, and East African plateaus. The first stage of rifting of the EAR was characterized by rift localization and magmatism along the entire rift zone. Periods of extension alternated with relative inactivity. There was also the reactivation of a pre-Cambrian weakness in the crust, a suture zone of multiple cratons , displacement along large boundary faults, and
1085-432: The sea floor. Its movement is concurrent with the EAR. Over time, many theories have tried to clarify the evolution of the East African Rift. In 1972 it was proposed that the EAR was not caused by tectonic activity, but rather by differences in crustal density. Since the 1990s, evidence has been found in favor of mantle plumes beneath the EAR. Others proposed an African superplume causing mantle deformation. Although
Ostrich - Misplaced Pages Continue
1120-410: The techniques of isotope geochemistry, seismic tomography and geodynamical modeling. The varying geochemical signatures of a suite of Ethiopian lavas suggest multiple plume sources: at least one of deep mantle origin, and one from within the subcontinental lithosphere. In accordance, a 2014 study compares the geochemical signature of rare earth isotopes from xenoliths and lava samples collected in
1155-455: The valley with sediments, creating a favorable environment for the preservation of remains. The bones of several hominid ancestors of modern humans have been found here, including those of " Lucy ", a partial australopithecine skeleton discovered by anthropologist Donald Johanson dating back over 3 million years. Richard and Mary Leakey have also done significant work in this region. In 2008, two other hominid ancestors were discovered here:
1190-554: The wild in Africa , where they occur in a range of open arid and semi-arid habitats such as savannas and the Sahel , both north and south of the equatorial forest zone. The Somali ostrich occurs in the Horn of Africa , having evolved isolated from the common ostrich by the geographic barrier of the East African Rift . In some areas, the common ostrich's Masai subspecies occurs alongside
1225-409: Was transferred to the genus Orientornis . Three additional species, S. pannonicus , S. dmanisensis , and S. transcaucasicus , were transferred to the genus Pachystruthio in 2019. Several additional fossil forms are ichnotaxa (that is, classified according to the organism's trace fossils such as footprints rather than its body) and their association with those described from distinctive bones
#11988