REVIEW OF GEOMORPHOLOGIC PROXIES FOR UPLIFT ON FLUVIAL SYSTEMS: A CASE STUDY FROM THE RWENZORI MOUNTAINS, THE EAST AFRICAN RIFT SYSTEM

Geomorphologic proxies yield meaningful insight into understanding the long term endogenic and exogenic response to rock uplift. However, uplift rates can only be described and quantified by these proxies under given sets of favorable conditions and by adopting certain theoretical assumptions. This study: (1) present the methodology to calculate these proxies from moderate resolution Digital Elevation Models (DEMs); (2) reevaluates the positive correlation between geomorphologic proxies for fluvial systems (hypsometric integral, shape factor, relief, length-gradient index, sinuosity index, asymmetry factor, valley floor width-to-height ratio, normalized steepness, and concavity); (3) outlines the advantages and limitations for each proxy; and. For this, we investigate thirteen drainage catchments from Rwenzori Mountains located within the Western Branch of the East African Rift System bounded by the Edward-George rift in the southeast and the Albertine graben to the northwest. We selected drainage catchments whose uplift rates is well-constrained to 28.2-131 mm/kyr by former workers using apatite (U–Th–Sm)/He ages, fission track and cosmogenic ¹⁰Be dating. The proxies are computed catchments drained by the Katonga and Semiki Rivers using 90 meters spatial resolution DEMs extracted from the Shuttle Radar Topography Mission (SRTM) data. Our preliminary results show that: (1) the length-gradient index and sinuosity index are well-correlated to the erosion and uplift rates in the drainage basins of the Rwenzori Mountains; (2) there are certain thresholds for the proxies to provide accurate information about the uplift rates. For example, relief and hypsometric integrals can only be positively correlated to rock uplift rate when the uplift rate is fast (70 mm/kyr); and (3) some proxies prone to be largely dependent to factors other than tectonics, climates or lithology such that the local relief is controlled by the slope and the hypsometric integral is sensitive to the size of the drainage catchments. By outlining the methodology of the extraction of these geomorphologic proxies and their pitfalls, the understanding of river response to rock uplift can be improved and the proxies that proved to be suitable for studying the Rwenzori Mountains can be applied to other sites in the East African Rift System.