Historical aerial photographs for landslide assessment: two case histories

Abstract

Abbreviated title:Aerial photographs for landslide assessment [Abstract] This paper demonstrates the value of historical aerial photographs for assessing long-term landslide evolution. The study focussed on two case histories, the Mam Tor and East Pentwyn landslides. In both case histories the variety of data was explored, 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 created products comprised geomorphological maps, automatically derived elevation models (DEMs), displacement vectors and animations.The measured horizontal displacements of the Mam Tor landslide ranged from 0.09-0.74 m/yr 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/yr 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 visualisation. Overall, the results in this study validated the techniques used and strongly encourage the use of historical photographic material in landslide studies. [End of abstract]Landslides include a range of slope movements, representing a widespread geological hazard. Yearly, extreme landslide disasters worldwide pose threats to people, infrastructure and cause significant economical losses. Growth of urban areas and expanded land use have increased the vulnerability of societies to landslides (Boullé et al. 1997;Smyth & Royle 2000). Moreover, the impact of climate change may result in higher frequencies of such events in the future (Dehn et al. 2000;Dixon & Brook 2007). Past research has identified different landslide mechanisms and many controls on their initiation and development (e.g. Varnes 1978;Crozier 1986). These controls are very complex and relate to climatic variables and characteristics of the slope, such as material, geological and hydrological conditions and vegetation cover. A full understanding of their interrelationships requires detailed and extensive monitoring of environmental factors and associated landform changes. Usually, long climate data records are available, whereas obtaining accurate historical spatial data quantifying landform change is a rather more challenging task.A combination of multi-temporal mapping of surface features and monitoring of landslide displacements may result in better understanding of their underlying mechanisms. There are sophisticated tools available for monitoring landslide movements. Traditional instruments include inclinometers, tiltmeters, extensometers and land surveyi...

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