CATCHMENT MORPHOLOGY VARIATION IN CONTRASTING UPLIFTS OF AN ACTIVE RIFT, LAKE TANGANYIKA, AFRICA

Source-to-sink studies provide constraints on sediment transport, tectonics and uplift, climate and erosion and depositional processes. A fundamental component of source to sink studies is catchment morphology. In rift systems, catchment morphology in general is controlled by the magnitude of footwall uplift, the bedrock geology and climate. These things vary on two scales: along the trace of a single normal fault and along the axis of the rift system in general. The prime purpose of this study is to calculate the size and gradient of catchments and analyze their variation along two opposing normal faults in the northern part of Lake Tanganyika of the East African Rift System. This will allow us to decipher influences on the catchment sizes and ultimately potential sediment yield, as well as the relationships between geomorphic parameters. We used the ALOS Global Digital Surface Model (AW3D30) DEM to delineate the river profiles and catchment areas of 130 catchments using ArcGIS and TopoToolbox programs. River profiles for each catchment were analyzed to locate knickpoints which are marked by the sudden change in longitudinal profile. Comparison between the two sides was done by the Curve Fitting Toolbox™ module to exhibit the tectonic differences and how it influences each of the components.

We documented trends among fault distance (from fault tip), catchment areas, longitudinal profiles of trunk streams and knickpoint distances from the shoreline. Along both footwall small catchment areas (~4 km²) exist up to 30 km from the designated fault tip, after which the catchment size increases. The knickpoint vs distance plot illustrates that knickpoint heights get farther upstream, farther from the fault tip along the eastern fault. However, the knickpoint heights show a more complicated trend on the west side. For instance, the knickpoint heights are higher (max ~7 km) within the southern part of the fault and drops in the middle section (~35-40 km) and increases again to the north. Plots of catchment area vs knickpoint distance (R² _East= 0.5202; R² _West= 0.709) suggests more significant relationship along the eastern fault block. Work is ongoing, but we conclude that the differences in trends suggest contrasts in uplift activity, or possibly climate, between these two footwall blocks on opposite sides of Lake Tanganyika.