LATERAL VARIATION IN DRAINAGE BASIN EVOLUTION ALONG AN ACTIVE RIFT MARGIN, LAKE TANGANYIKA, AFRICA

Drainage basin morphology is strongly affected by both surficial and tectonic processes. Geomorphic features, such as knickpoints along a river’s course, are often a result from both processes and act as a spatial and temporal marker for tectonic activity within drainage basins. This is particularly true for extensional systems where rates of footwall uplift vary along strike of the fault segment as well as over time. This study aims to use area-elevation relationships and hypsometric curves to determine the lateral variation of drainage basin maturity along strike of a normal fault bordering Lake Tanganyika. We used GIS tools to analyze a DEM of 38 drainages that deposit into the lake. As a result, both the hypsometric curve and the hypsometric integral (HI) was calculated for each drainage. HI values ranged from 0.3 to 0.65, therefore displaying a variety of erosion potential across drainages. 68% of drainages have HI values from 0.45 to 0.55 and are therefore classified as being in the mature stage. But unlike the drainages that are either >0.40 or <0.60, those within this range seem to have the greatest variability with respect to concavity across elevation within individual drainages. By relating concavity of the curves to the spatial position of identified knickpoints, we interpret which elevations along these drainages are experiencing the greatest amounts of denudation. While some show mature to older hypsometric curves, additionally they exhibit an S-shape morphology indicating a geomorphic feature. The elevation of the hypsometric inflection points within the drainages may also be a function of knickpoint migration exhibited by an inflection point along the curve that concaves downward. Identifying these geomorphic features, and understanding their lateral variation with respect to the length of the fault segment, helps explain where the greatest amount of sediment generation occurs and eventually deposited into the lake.