Submarine canyons of NW Madagascar: A first geomorphological insight

The continental slope of Madagascar is underrepresented in the literature in comparison to other continental slopes worldwide. In particular, the submarine geomorphology of this zone has not been discussed in detail. During research cruise 50230 approximately 1900 km(2) of high resolution multibeam bathymetric data were collected along the northwest continental slope of Madagascar. These data show four, previously unrecognised, submarine canyons extending to the toe of the continental slope in the eastern Mozambique Channel. Measured canyon thalweg lengths vary from 40 to 51 km and exhibit straight to sinuous paths. The thalweg profiles include concave, linear and slightly convex characteristics. Canyon relief decreases with depth downslope, while canyon width increases. The interfluves of the upper canyon reaches are dominated by large, square to rectangular, block-like features of 100-200 m vertical relief. These features decrease in prominence down slope. Canyons mark the coast-perpendicular flank of the blocks, while the coast-parallel block flanks are delineated by elongate valleys. The geomorphology of the canyons is best explained by varied stages (youthful to mature) of canyon evolution. The discovery of these canyons highlights the complexity of the Madagascan Continental slope, and the future potential for multidisciplinary research in this region.