The Age and Tectonic Relationships of East African Volcanic Rocks

1944 ◽  
Vol 81 (1) ◽  
pp. 15-27 ◽  
Author(s):  
P. E. Kent

The great volume of extrusive rocks which has accumulated during and since the Tertiary period is one of the most important geological features of East Africa, and one which various people have related to the formation of the Rift Valley System.

Author(s):  
John Galaty

The Rift Valley is a stage on which the history of Eastern Africa has unfolded over the last 10,000 years. It served as a corridor for the southward migration from the Upper Nile and the Ethiopian highlands of Nilo-Saharan and Afro-Asiatic speakers and cultures, with their domestic animals, which over time defined and restructured the social and cultural fabric of East Africa. Genetic evidence suggests that, contrary to other regions in Africa where geography overrides language, the clustering of East African populations primarily reflects linguistic affiliation. Eastern Sudanic Nilotic speakers are dedicated livestock keepers whose identification with cattle over thousands of years is manifested in elaborate symbolism, networks created by cattle exchange, and the practice of sacrifice. The geographical attributes of rich grasslands in a semi-arid environment, close proximity of lowland and highland grazing, and a bimodal rainfall regime, made the Rift Valley an ideal setting for increasingly specialized pastoralism. However, specialized animal husbandry characteristic of East Africa was possible only within a wider socioeconomic configuration that included hunters and bee-keeping foragers and cultivators occupying escarpments and highland areas. Some pastoral groups, like Maasai, Turkana, Borana, and Somali, spread widely across grazing areas, creating more culturally homogeneous regions, while others settled near one another in geographically variegated regions, as in the Omo Valley, the Lake Baringo basin, or the Tanzanian western highlands, creating social knots that signal historical interlaying and long-term mutual coexistence. At the advent of the colonial period, Oromo and Maasai speakers successfully exploited the ecological potential of the Rift environment by combining the art of raising animals with social systems built out of principles of clanship, age and generation organizations, and territorial sections. Faced with displacement by colonial settlers and then privatization of rangelands, some Maasai pastoralists sold lands that they had been allocated, leading to landlessness amid rangeland bounty. Pastoral futures involve a combination of education, religious conversion, and diversified rangeland livelihoods, which combine animal production with cultivation, business, wage labor, or conservation enterprises. Pastoralists provide urban markets with meat, but, with human population increasing, per capita livestock holdings have diminished, leading to rural poverty, as small towns absorbing young people departing pastoralism have become critical. The Great East African Rift Valley has had a 10,000-year history of developing pastoralism as one of the world’s great forms of food production, which spread throughout Eastern Africa. The dynamics of pastoral mobility and dedication to livestock have been challenged by modernity, which has undermined pastoral territoriality and culture while providing opportunities that pastoralists now seek as citizens of their nations and the world.


Author(s):  
G. T. Prior

The following notes on the petrology of British East Africa are the result of an examination of rock-specimens collected by Professor J. W. Gregory on his well-known expedition from Mombasa to Mt. Kenya and Lake Baringo in 1892-3, and of rock-collections from the Uganda Protectorate which have been recently presented to the British Museum by Sir Harry Johnston.The collections include examples of the Archaean gneisses, schists, and granites which constitute the prevailing basement rocks of Central Africa; of ferruginotls schists, coarse sandstones, and quartzites belonging to the Palaeozoic Karagwe series ; and of an interesting series of Tertiary volcanic rocks comprising phonolites, phonolltic traehytes, riebeckite-rhyolites, kenytes, and basalts from the volcanoes of the Great Rift Valley, as well as of nephelinites and basaltic rocks containing melilite and perofskite from Mr. Elgon.


1981 ◽  
Vol 18 (2) ◽  
pp. 330-341 ◽  
Author(s):  
C. S. Churcher

The Olduvai zebra, Equus oldowayensis, is identified or confirmed from the following sites: Olorgesailie, Lake Magadi; Marsabit Road, Northern Kenya; Chemoigut Beds (Chesowanja), Baringo Basin; Wajir, Northeast Kenya; Bura, Tana River; Makalia River (MacInnes Site), Rift Valley; Legetet, Koru; Karmosit, Suguta River; and Kanjera, Homa Mountain, all in Kenya, on the evidence from isolated teeth and other fragments. Burchell's zebra, E. burchellii, appears to have been absent from all the sites except possibly Olorgesailie and the Chemoigut Beds.E. oldowayensis is known from about 1.8 Ma ago in Bed I at Olduvai Gorge and from about 1.9 Ma ago in the Shungura Formation (Member G) in the Omo deposits, before which no reliable records are recognised. It was the common and dominant zebra of the latest Pliocene and Pleistocene in the East African plains and was replaced by the present common zebra, E. burchellii, only during the latest Pleistocene and Holocene times. E. oldowayensis is similar to modern Grevy's zebra, E. grevyi, to which it gave rise, and these two zebras are not directly related to Burchell's zebra.


2005 ◽  
Vol 32 ◽  
pp. 199-220 ◽  
Author(s):  
Christian Jennings

During the early nineteenth century, European travelers and residents in east Africa wrote of an important pastoralist society, called Loikop, that dominated the plains of the Rift Valley, and whose divisions included, among others, the rapidly expanding Maasai. These pastoralists were described in detail by three missionaries: Johann Ludwig Krapf, Johannes Rebmann, and Jakob Erhardt. Their various journals, letters, and published articles, written during the 1840s and 1850s, are widely recognized as the earliest documentary evidence for Maasai and Parakuyo history. But they have often been neglected, and sometimes deliberately shunned, in favor of later written or oral sources, perhaps because their views of pastoralist history, including the idea of a pastoralist Loikop community, seem rather incongruous when compared to those of more recent vintage.This skepticism was fueled partly by the fact that during the course of the nineteenth century, Maasai expanded dramatically, demolishing and absorbing other Loikop sections; eventually, Maasai pastoralist identity superseded and erased that of Loikop. By the time of European colonial conquest, the term “Loikop” carried negative connotations, and scholars from this point forward had difficulty in seeing any other valid meaning for the term. This essay is devoted to making the case for restoring the idea of Loikop pastoralists in our narratives of east African history. In many ways, it is a response to John Berntsen's “The Enemy Is Us: Eponymy in the Historiography of the Maasai,” published in 1980.


By means of the methods of Lewis & Dorman (1970), the isostatic response has been computed for an area 800 km square of East Africa, surrounding the Kenya rift valley. By applying linear programming to the inversion of these data, it can be shown that local compensation models involving only negative density contrasts fit the response data at confidence levels of up to 80%. Comparison of the gravity anomalies of the compensation with the results of seismic array measurements made by Long & Backhouse (1976) shows that the East African plateau is compensated differently from the highland region around the rift valley known as the Kenya dome. The dome is supported by a region of the mantle with low density, low seismic P velocity, and high electrical conductivity, almost certainly a zone of partial melting. The linear programming technique can be used to show that, to satisfy the data, the top of the anomalous zone must be no deeper than 55 km. If the density anomaly is entirely due to melting, the average melt concentration in the uppermost 50 km of the mantle must exceed 6%.


Transfers ◽  
2015 ◽  
Vol 5 (2) ◽  
pp. 102-120
Author(s):  
Michael Pesek

This article describes the little-known history of military labor and transport during the East African campaign of World War I. Based on sources from German, Belgian, and British archives and publications, it considers the issue of military transport and supply in the thick of war. Traditional histories of World War I tend to be those of battles, but what follows is a history of roads and footpaths. More than a million Africans served as porters for the troops. Many paid with their lives. The organization of military labor was a huge task for the colonial and military bureaucracies for which they were hardly prepared. However, the need to organize military transport eventually initiated a process of modernization of the colonial state in the Belgian Congo and British East Africa. This process was not without backlash or failure. The Germans lost their well-developed military transport infrastructure during the Allied offensive of 1916. The British and Belgians went to war with the question of transport unresolved. They were unable to recruit enough Africans for military labor, a situation made worse by failures in the supplies by porters of food and medical care. One of the main factors that contributed to the success of German forces was the Allies' failure in the “war of legs.”


2021 ◽  
Vol 41 (2) ◽  
Author(s):  
Maren Vormann ◽  
Wilfried Jokat

AbstractThe East African margin between the Somali Basin in the north and the Natal Basin in the south formed as a result of the Jurassic/Cretaceous dispersal of Gondwana. While the initial movements between East and West Gondwana left (oblique) rifted margins behind, the subsequent southward drift of East Gondwana from 157 Ma onwards created a major shear zone, the Davie Fracture Zone (DFZ), along East Africa. To document the structural variability of the DFZ, several deep seismic lines were acquired off northern Mozambique. The profiles clearly indicate the structural changes along the shear zone from an elevated continental block in the south (14°–20°S) to non-elevated basement covered by up to 6-km-thick sediments in the north (9°–13°S). Here, we compile the geological/geophysical knowledge of five profiles along East Africa and interpret them in the context of one of the latest kinematic reconstructions. A pre-rift position of the detached continental sliver of the Davie Ridge between Tanzania/Kenya and southeastern Madagascar fits to this kinematic reconstruction without general changes of the rotation poles.


The Lake Rudolf Rift Valley Expedition was designed to carry out many different lines of investigation in the Lake Rudolf Basin. One of the chief of these was a study of the geological history of that part of the East African Rift Valley. The expedition was assisted financially by The Royal Society, The Geological Society of London, The Royal Geographical Society, The Percy Sladen Trustees and the Geographical and Geological Sections of the British Association. A general description of the activities of the Expedition was given in a paper read before the Royal Geographical Society (Fuchs 1935). Owing to the tragic loss of two members of the expedition, Dr W. S. Dyson and Mr W. R. H. Martin, two fruitless months were spent searching for them. Consequently a great amount of the work planned for the east side of the lake had to be abandoned. Nevertheless, the considerable distance travelled within the 50,000 sq. miles of the Rudolf Basin has enabled me to make out the chief events of its geological history. I am very much indebted to all those who assisted us in the field and at home, in particular to the Kenya Government, the Officers of the King’s African Rifles, and Mr H. L. Sikes of the Public Works Department; I would also like to thank Mr A. M. Champion, Provincial Commissioner of Turkana, who wholeheartedly assisted us in every way possible both in the field and at home, for he has placed at my disposal his own excellent topographical maps and his extensive observations on the geology of the area. I am also deeply indebted to Professor O. T. Jones, Mr Henry Woods and Mr W. Campbell Smith for their criticisms. Mr Campbell Smith has also given me provisional identifications of the rocks.


1941 ◽  
Vol 78 (3) ◽  
pp. 173-184 ◽  
Author(s):  
P. E. Kent

ONE of the objectives of the East African Archaeological Expedition of 1934–5 was the examination of the plateau north of Lake Eyasi—the Vogel River area—where, it was hoped, a continuation of the richly fossiliferous Oldowaya Middle Pleistocene lake beds would be found. This hope was essentially realized ; deposits with an interesting Middle Pleistocene fauna a little earlier than that of Oldoway were found, with the difference that they were entirely terrestrial. The development of precisely datable beds resting upon a main Rift Valley Scarp made possible a study of physiographical changes associated with the faulting.


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