STEADY-STATE BEHAVIOR OF THE BLACK-VEN MUDSLIDE - THE APPLICATION OF ARCHIVAL ANALYTICAL PHOTOGRAMMETRY TO STUDIES OF LANDFORM CHANGE

The concept of dynamic equilibrium has provided geomorphologists with a challenging paradigm for studying landform evolution but quantitative evidence for its existence has proved illusive, particularly for complex geomorphological systems, The authors believe that the principle has now been verified through the application of the 'archival photogrammetric technique' to a sequence of historical photographs spanning 50 years of process at the Black Ven mudslide complex in Dorset, U.K. The principles and limitations of the archival photogrammetric technique are described. The method is applied to oblique and vertical aerial photographs of Black Ven at five epochs, commencing in 1946, continuing at approximately 10 year intervals until 1988. The technique is used to generate plans/contours/sections and a dense and accurate digital elevation model (DEM) of the whole site at each epoch. This is used to generate 'DEMs of difference' and a 'distribution of slope angle' which suggest that the mudslides are in equilibrium despite the removal of 200 000 m(3) of sediment between 1958 and 1988. Extrapolation of the slope distribution through time suggests that the frequency of an episodic landform change model at Black Ven may be approximately 60 years.