GEOGRAPHIC CONTEXT OF THE NAMORATUNGA
Africa showing country borders and the position of the Sahel, the bright yellow-brown band beneath the Sahara Desert.
The sites we will focus on are in northwest Kenya, where you can just make out Lake Turkana if you look carefully.
|2. The Intertropical Converg- ence Zone (ITCZ or ICZ), showing its average position in January and July. If you look at the fiery image at the top of this page, you will see the ITCZ is marked by a bright yellow-orange band crossing the center of the map.
The ITCZ mediates many features of the environment that constrain human adaptation in the Sahel and Eastern Africa.
|3. A closer view of what the ITCZ looks like from orbit in early August. In this region the dominant weather patterns move from east to west north of the Zone and from west to east south of the Zone.|
|4. Another shot of the ITCZ taken in early August showing the early development of a tropical storm.|
|5. The top half of this image shows a cross section of the Earth's atmosphere from 30° South to 60° North. The ITCZ is an irregular avenue of air at the equator and the tropical hot air masses on either side are parallel tubes called Hadley Cells that facilitate the mixing of the atmosphere between the equatorial and polar regions of the Earth.
In the lower part of the image, the dark band that traverses Aftica and the Indian Ocean is the northern Hadley Cell. The darker band in the South Adlantic and portions of Southern Africa is the southern Handly Cell. It is disrupted over Central Africa and the southern Indian Ocean.
|6. This figure shows the interaction between three great air bodies. North of the ITCZ, the arrows depict the normal east-to-west air flow that characterizes the northern hemisphere. To the south of the ITCZ, the west-to-east air flow off the southern Atlantic Ocean collides with the Indian monsoon, which rotates over the southern Indian Ocean and sweeps inland over Eastern and Central Africa, disrupting the flow of air in and around the southern Hadley Cell.|
|7. This image depicts how much wetter and drier various parts of Africa were in the early part of the Holocene period, around 8,000 years ago. As you can see, the southern Sahara and Sahel are thought to have received 250 to 450 mm. more in rainfall per annum.|
|8. This period of elevated rainfall sustained thousands of lakes and marshes, many of which are large enough to be mapped even at continental scales, as we see here. Together with the adjoining savannah and step, they supported first hunters and fishers, and later, by about 7,600 years ago, pastoralists who herded cattle and soon added sheep and goats to their herds.|
|9. The sediments from these lakes show that rainfall declined precipitously beginning around 5,500 years ago. This decline puts a great deal of pressure on the human inhabitants of the Sahara and the Sahel. New economic adaptations, reduction overall population levels, and out migration are among the adaptive responses. It also sets the stage for the consolidation of Egyptian civilization, but that's another story.|
|10. This Linguistic map of Africa shows the southward expansion of languages from the Sudan and Ethiopian Highlands into the East African savannah corridor.|
|11. The Nile Basin. The red arrow points to Lake Turkana around which are found the eight known Namoratunga - the focus of this course.|
|11A. The Nile Basin. This satellite image shows the Nile corridor where one of the earliest known agricultural civilizations developed. The relationship between stock-keeping and agricultural populations is highly structured by access to and through this corridor.|
|12. The northern Rift, showing Lake Turkana and surrounding regions.|
|13. Lake Turkana late in 2009 after prolonged drought.|
|14. Lake turkana during an unusually intense wet season. Image dates from August 21, 2006.
Compare the dry season image taken on July 13, 2006.
©2009 by Charles M. Nelson|
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