Results of high-resolution echo-sounding of Lake Victoria

Abstract

About 1800 km of reconnaissance echo-sounder data have been collected from Lake Victoria. The profiles show a maximum open-basin thickness of 8 m oatest Pleistocene and Holocene fine-grained muds. Their distribution mimics bathymetry, except for locally thicker patches around bathymetric highs, which serve as current and seiche breaks. The transparent sediment blanket overlies an acoustic basement that ranges from crystalline basement to a late-Tertiary, boulder-studded peneplain to coarser-grained lacustrine sediments and dewatered fine-grained mudstones, depending upon position in the lake. Correlation to discontinuities in core data suggest that the boundary between the fine-grained, acoustically transparent muds and acoustic basement represents a 14,000 year old desiccation surface of essentially lake-wide extent. Many curious signatures are noted in the Lake Victoria echograms, including spiky diffractions that may represent buried boulders or gas escape structures; megaripples and sediment wave bedforms associated with current activity in the SW corner of the lake; and a tilted-block terrain in the Speke Gulf that is probably caused by recent submergence of subaerially eroded Archean crystalline rocks along uniformly-spaced joints and fractures.