Retreat of the Great Escarpment of Madagascar From Geomorphic Analysis and Cosmogenic 10Be Concentrations

The eastern margin of Madagascar has a prominent relief change from the flat coastal plain to the low-relief high plateau, characterizing a typical great escarpment topography at a passive margin. A quantification of the spatial distribution of erosion rates is necessary to understand the rate of landscape evolution. We present catchment-averaged erosion rates from detrital cosmogenic Be-10 concentrations, systematically covering distinct morphological zones of the escarpment. Erosion rates are differentiated across the escarpment, where the high plateau and the coastal plain are slowly eroding with an average rate of 9.7 m/Ma, and the escarpment basins are eroding faster with an average rate of 16.6 m/Ma. The Alaotra-Ankay Graben related basins have the highest erosion rate with an average rate of 27 m/Ma. The spatial pattern of erosion rates indicates a retreating escarpment landscape. Retreat rates calculated from the Be-10 concentrations are from 182 to 1,886 m/Ma. The rates of escarpment retreat on Madagascar are consistent with a model of a steady retreat from the coastline since the time of rifting, similar to the Western Ghats escarpment on its conjugate margin of the India Peninsula.

Automated summary

The eastern escarpment of Madagascar shows varying erosion rates across different regions, with slower rates on the high plateau and coastal plain, and faster rates in the escarpment basins, particularly in the Alaotra-Ankay Graben basins. The spatial pattern indicates a retreating escarpment landscape, with retreat rates consistent with a model of steady retreat since the time of rifting.