Madagascar's landscape evolution: A tale of two rifts.

Abstract

The topography of Madagascar reflects a dynamic history of water divide migration, initially driven by rift events on both coasts separated by ~80 million years and later modified by Late Cenozoic volcanic and tectonic activity. This study examines how rifting-induced tilting of an escarpment-plateau landscape led to changes in drainage area and water divide positions. Combining topographic analysis and erosion rates inferred from cosmogenic isotope concentrations, we document a westward-tilted low-relief plateau with sinuous remnant escarpments along the western margin and a linear, high-relief escarpment corresponding to the modern drainage divide on the eastern margin. Our numerical modeling demonstrates that landscape asymmetry and contrasting escarpment morphology can result from a shift in the main water divide across the island during the second rifting event. These mechanistic processes allow us to reconstruct the landscape evolution of Madagascar over more than 100 million years with profound implications for the topography, hydrology, and biodiversity development of passive continental margins.