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Détails
Delvaux, D. 1995. ‘Age of Lake Malawi (Nyasa) and water level fluctuations’. Mus. roy. Afr. centr. Tervuren (Belg.), Dept. Géol.-Min., Rapp. ann 1993-1994: 99-108.
Article dans une revue scientifique / Article dans un périodique
Lake Malawi (Nyasa) is one of the few deep-water long-lived lakes that presently exist on earth. It lies in an uncompensated tectonic graben, controlled by differential vertical movements between the rift basin who subsides and the rift shoulders who are uplifted. Active tectonics is the major factor controlling the development and persistence of those deep lakes. For Lake Malawi (Nyasa), climatic influence is also important, due to the small dimensions of the hydrological catchment area and the subtropical climate with long dry seasons. The Malawi rift basin, hosting the lake, started to develop in the late Miocene (since 8.6 Me), but deep water conditions were acquired only by 4.5 Ma. The lake then dried out almost completely at the beginning of the Pleistocene (from 1.6 to 1.0 Ma), as a consequence of stable tectonic conditions and dry climate. A new regression started at about 0.42 Ma until 0.25 Ma, which is well documented by high-resolution seismic stratigraphy. The tectonic lowering of the overflow sill, through subsidence of the rift floor, combined with erosional incision have lowered the water level by 40m since the late Pleistocene. Short-term, small amplitude lake-level fluctuations are documented by direct observations since 1915.