Morphological evolution of Cap Lopez Canyon (Gabon): Illustration of lateral migration processes of a submarine canyon

Comparison of bathymetric data on short time scales (1959–2008) is used to provide new insights into the modern sedimentary dynamics of the Cap Lopez Canyon (Gabon, West Africa). The canyon head evolution is characterized by a north–eastward lateral migration of ~ 180 m between 1959 and 2008. The evolution of the coastline position over the same period highlights the strong relationship between the probable increase of the longshore transport, related to the smoothing of the coast and the morphological evolution of the canyon head. Lateral migration of the thalweg from the inner bend to the outer bend is estimated between 77 and 190 m (or between 1.6 and 3.8 m/year), leading to an increase of the sinuosity (from 1–1.5 in 1959 to 1.3–3.6 in 2008). The migration of the thalweg is associated with strong erosion on the outer bends (up to 60 m) and sediment deposition on the inner bends (up to 25 m). Both the absence of overbank deposits and the developing point-bar morphology may reflect that equilibrium flows are the most frequent flows encountered in the Cap Lopez Canyon. Although erosion of the outer bends is the result of slope failures and steady erosional processes, our study suggests that erosion related to the transit of sediment gravity flows would be the predominant process.