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Abstract

GIS-based techniques of digital spatial data analysis are applied to quantify longterm average rates of surface lowering (denudation) for a 710 km2 large area within the Bahati-Kinangop-Plateau in the Central Kenya Rift. The plateau is an ideal site for assessing longterm denudation rates due to the conservation of well dated relict erosional remnants forming the top part of the present plateau surface. Since an idealized non-eroded initial plateau surface can be estimated from these relict surface elements, the present relief is a measure of the eroded material since the formation of the plateau began between 3.4 and 2.6 Million years ago. In contrast to traditional analog methods, digital surface modelling techniques are used in a GIS-environment to calculate denudation rates based on the described elevation difference approach. Methodological emphasis is on the digital generation of good quality surfaces from contours and the quantitative accuracy assessment of products from the multi-stage GIS-based analysis. The digital environment allows development of a sensible approach producing well understood results at high spatial resolution. They vary from 1--10 m/Ma (meter per Million years) for little eroded to 20--50 m/Ma for deeply eroded parts of the plateau. These denudation rates reflect the natural variation in magnitude of exogenic geomorphologic processes and are the basis for further regional analysis within a GIS.