2.4. Slope statistics calculations
We calculated two types of slopes, absolute and differential, at different baselines on the selected topographic profiles. For all possible combinations of two points in a given topographic profile, the absolute slope was calculated from the difference of elevation between the two points and the distance between them, calculated from their geographic coordinates. A discrete number of baseline ranges, from the smallest point-to-point distance available to about 100 km, was finally defined. Slope distributions could then be displayed for all baseline ranges (Fig. 2 and 3) and statistical parameters, in particular the Median of the Absolute Slope distribution (MAS), calculated for each baseline range (Fig. 4).
In a similar way, we calculated Median Differential Slope (MDS) distributions following the definition proposed by Kreslavsky and Head (2000). For a given point p of the profile
and a given baseline l, a slope a is calculated from the difference
of altitude h between the points located at a distance l/2 before (h - l/2) and after (hl/2) point p. The same calculation is then made for twice the baseline l, i.e. between point - l and þ l. The differential slope between these two baselines can thus be