page_title: African humid period
section_title: East Africa
hierarchical_section_title: African humid period / Effects / East Africa
caption_attribution_description: English: The main glacier on the top of Kilimanjaro as seen in Feb of 2012.
context_page_description: The African humid period is a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, trees and lakes was caused by changes in Earth's orbit around the Sun; changes in vegetation and dust in the Sahara which strengthened the African monsoon; and increased greenhouse gases, which may, or may not, imply that anthropogenic global warming could result in a shrinkage of the Sahara desert.
  During the preceding last glacial maximum, the Sahara contained extensive dune fields and was mostly uninhabited. It was much larger than today, but its lakes and rivers such as Lake Victoria and the White Nile were either dry or at low levels. The humid period began about 14,600–14,500 years ago at the end of Heinrich event 1, simultaneously to the Bølling-Allerød warming. Rivers and lakes such as Lake Chad formed or expanded, glaciers grew on Mount Kilimanjaro and the Sahara retreated. Two major dry fluctuations occurred; during the Younger Dryas and the short 8.2 kiloyear event. The African humid period ended 6,000–5,000 years ago during the Piora Oscillation cold period.
context_section_description: Nile discharge was higher than today and during the early African humid period, the Nile in Egypt flooded up to 3–5 metres (9.8–16.4 ft) higher than it did recently before flood control; the increased flooding may explain why many archeological sites along the Nile were abandoned during the AHP, with violent conflicts reconstructed from the Jebel Sahaba archeological site. Waters from the Nile filled depressions like the Fayum Depression. In addition, Nile tributaries in northwestern Sudan such as Wadi Al-Malik, Wadi Howar and Valley of the Queens became active during the AHP. Wadi Howar was active until 4,500 years ago, and at the time often contained dune-dammed lakes, swamps and wetlands; it was the largest Saharan tributary of the Nile and constituted an important pathway into sub-Saharian Africa. Conversely it appears that Lake Victoria and Lake Albert were not overflowing into the White Nile for all of the AHP, and the White Nile would have been sustained by overflow from Lake Turkana. There appears to be a tendency over the course of the AHP for the discharge of the Blue Nile to decrease relative to that of the White Nile. The Blue Nile built an alluvial fan at its confluence with the White Nile, and incision by the Nile reduced flooding risk in some areas which thus became available for human use.
  Closed lakes in East Africa rose, sometimes by hundreds of metres. Lake Suguta developed in the Suguta Valley, accompanied by the formation of river deltas where rivers such as the Baragoi River entered the lake. In turn, Lake Suguta overflowed into the Kerio River, this adding water to Lake Turkana where increased discharge by the Turkwel River led to the formation of a large river delta. Lake Turkana itself overflowed on its northwestern side through the Lotikipi Swamp into the White Nile. Deposits from this lake highstand form the Galana Boi Formation. This overflowing large lake was filled with freshwater and was populated by humans; the societies there engaged in fishery but could probably also fall back on other resources in the region. Lake Zway and Lake Shala in Ethiopia joined with Lake Abiyata and Lake Langano to form a large waterbody which began overflowing into the Awash River. Other lakes that expanded include Lake Hayq also in Ethiopia, Lake Bogoria, Lake Naivasha and Lake Nakuru/Lake Elmenteita all in Kenya, and a lake formed in the caldera of the Menengai volcano. A 1,600 square kilometres (620 sq mi) large and 50 metres (160 ft) deep Lake Magadi formed in the early Holocene, and in the Danakil Depression of Ethiopia freshwater conditions became established. Finally, lakes formed in depressions on the mountains around Lake Kivu.
  Glaciers on Mount Kilimanjaro expanded during the AHP after a phase during the Younger Dryas where the mountain was ice free, but the tree line also rose at that time, accompanied by soil formation. The wetter climate may have destabilized the neighbouring Mount Meru volcano, causing a giant landslide that removed its summit.
  Erosion in catchments of East Africa increased with the beginning of the humid period but then decreased even before its end, as the increased weathering led to the formation of soils, these in turn to the establishment of a vegetation cover that subsequently reduced additional erosion. Increased weathering resulted in the increased consumption of atmospheric CO2 during the AHP.
  Surprisingly, and contrary to the patterns expected from precessional changes, the East African Rift also experienced a wetter climates during the AHP, reaching as far south as Lake Rukwa and Lake Cheshi into the Southern Hemisphere. In the region of the African Great Lakes, pollen evidence points to the occurrence of forests including rainforest vegetation due to the increased precipitation, while today they occur only in limited areas there. Denser vegetation also occurred at Lake Turkana, with wooden vegetation covering almost half of the dry land. Development of forest vegetation around the African Great Lakes created an interconnected environment where species spread, increasin
caption: A glacier on Mount Kilimanjaro. The oldest now present ice of Kilimanjaro formed during the African humid period
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