アイテム詳細

要旨

There are numerous mountain ranges in Africa which carry evidence of Quaternary glaciation, though few have glaciers now and these are rapidly disappearing. The best studied sites are in East Africa and Ethiopia. In East Africa, the three highest mountains, Kilimanjaro, Kenya and the Rwenzori, each have evidence of 3-5 major glaciations dating back to an estimated 400,000 BP, one of which is dated to the Last Glacial Maximum (LGM) by radiocarbon or cosmogenic radionucleide (CRN) methods; two other mountains have similar large moraine systems inferred to date to the LGM. In Ethiopia, three mountains have clear evidence of glaciation and on two of them radiocarbon dates give minimum ages which suggest that these are LGM features. In North Africa, the Atlas and other groups of mountains have evidence of glaciation but, in the absence of any dating, it is unclear whether these sites were glaciated at the LGM. Although geomorphic features resembling moraines and protalus ramparts have been described from the Drakensberg Mountains, South Africa, it is still unclear whether these features indicate glaciation and can be attributed to the LGM. Thus, although circumstances for fieldwork on African mountains are very difficult in many cases, investigations for more than a century provide an extensive picture of Quaternary glaciation. In some cases, there has been an increasingly detailed mapping of field evidence and the first CRN dates were carried out recently, thus improving the global picture considerably. Particularly in East Africa and Ethiopia there is sufficiently reliable field information to make useful estimates of equilibrium line altitude changes at the provisionally identified LGM, but this age needs confirmation by further CRN dating. By making some hypothetical assumptions, inferences can be drawn that indicate a temperature lowering of 5-6 degrees C during the LGM. Elsewhere in Africa, further field surveys are required. (c) 2005 Elsevier Ltd and INQUA. All rights reserved. [References: 83]