Megafloods and Megalakes on the Okavango Megafan in the Makgadikgadi-Okavango-Zambezi Basin, Botswana

Authors: Robert Bean*, University of Texas - Austin
Topics: Geomorphology, Paleoenvironmental Change
Keywords: paleohydrology, soil geomorphology, southern Africa, megafans
Session Type: Paper
Day: 4/11/2018
Start / End Time: 8:00 AM / 9:40 AM
Room: Napoleon B2, Sheraton 3rd Floor
Presentation File: No File Uploaded

Flooding patterns of the MOZ (Makgadikgadi-Okavango-Zambezi Basin) of northern Botswana are a local concern but moreover of global interest, underscored by the Delta’s status as one of under 70 wetlands globally that have both Ramsar and UNESCO World Heritage status. Previously, these three areas connected to form a megalake, Lake Makgadikgadi, several times larger than the U.S. Great Lakes today and residing along borders of the Okavango Delta, which terminates in the Mababe Depression, the Makgadikgadi Pans, or Lake Ngami. Despite consensus that a giant lake existed, disagreements remain on when and how it was filled. Examination of the present state of the delta’s edge and how the delta moved in the past are critical. MOZ edges are sensitive to climate and therefore can be used to assess climatic variability in ways not previously explored or – more importantly – not possible to examine in other locations and further complicated by precipitation varying up to 80-90% annually. This paper gives an overview of geomorphic surfaces and their subsurface expressions through fieldwork excavating 31 different soil pits throughout the distal portion of the MOZ in northern Botswana. Specifically we examine Lake Ngami, where a combination of 14C dating, δ13C isotope analysis, magnetic susceptibility, and XRF/XRD analysis show a distinct surface spanning 3.0-4.4 ka YBP when sedimentation increased tenfold their subsequent and present day rates. These allow for an improved and novel understanding of dynamics at a finer spatial and temporal scale by leveraging intensive fieldwork and a uniquely positioned megafan system.

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