Abstract

This paper demonstrates the value of historical aerial photographs for assessing long-term landslide evolution. The study focused on two case histories, the Mam Tor and East Pentwyn landslides. In both case histories we explored the variety of data that could be derived relatively easily using an ordinary PC desktop, commercially available software and commonly available photographic material. The techniques to unlock qualitative and quantitative data captured in the photographic archive were based on the principles of aerial photo-interpretation and photogrammetry. The products created comprised geomorphological maps, automatically derived digital elevation models (DEMs), displacement vectors and animations. The measured horizontal displacements of the Mam Tor landslide ranged from 0.09 to 0.74 m a−1 between 1953 and 1999, which was verified by independent survey data. Moreover, the observed displacement patterns were consistent with photo-interpreted geomorphological information. The photogrammetric measurements from the East Pentwyn landslide (horizontal displacements up to 6 m a−1 between 1971 and 1973) also showed a striking resemblance to independent data. In both case histories, the vertical accuracy was insufficient for detecting significant elevation changes. Nevertheless, DEMs proved to be a powerful tool for visualization. Overall, the results in this study validated the techniques used and strongly encourage the use of historical photographic material in landslide studies.

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