Seventeen years of the “La Clapière” landslide evolution analysed from ortho-rectified aerial photographs

Abstract

We present a new method of digital elevation model (DEM) calculation from aerial photographs and apply this method to the La Clapière landslide in the Mercantour Massif in eastern France. The method uses new techniques of image correlation and of restitution of camera parameters. The calculated DEMs are used to ortho-rectify three aerial photographs acquired between 1983 and 1999. Measurements, made from these ortho-rectified images, show that the average velocity of the landslide was of 1.7 cm/day, with the rate of the headscarp retreat of 4.1 cm/day, and the toe of the landslide advancing at 1.7 cm/day, between 1983 and 1999. Within the landslide, the velocity field is relatively homogeneous, although their directions are locally heterogeneous. Scree slopes and scarps develop in an heterogeneous way within the landslide. Because the headscarp moves faster than the front of the landslide, material spreads laterally at the scree slopes, and/or is eroded at the front of the landslide by the river, and/or is accumulated within the landslide, on a low slope area located above a competent bar called Iglière bar.