illustrating massive cliff recession and coastal change
Surface change models
The area west of the Charmouth Heritage Coast Centre
is known as Black Ven, and is not just a source of fossils and diverse plants.
It is also a site that has undergone massive physical change over the
last 60 years, including 80 metres of cliff recession- virtually the length of a
These changes are due to the underlying unstable
geology and rain that has created the largest coastal mudslide complex in
Europe. Three massive mudslide systems have transported thousands of
cubic metres of rock, mud (and fossils) onto the beach, which has then been
transported along the coast, eventually contributing to Chesil beach.
Occasionally these events have been cataclysmic with large rotational failures
removing large sections of the cliff within seconds. More gradually, but equally
dramatically, rivers of rock and quick-sand literally flow down the cliff in the
wet winter months, forming huge lobes of mud which penetrate the sea. Although the area is potentially lethal in
the winter the mud normally sets hard
over the summer and is then comparatively safe.
photography and photogrammetry
The timing and extent of change on Black Ven has been measured using historic aerial photographs and photogrammetry, a technique used by the Ordnance Survey for the production of maps. Historical aerial photographs present a unique and under utilised resource for detecting change within the landscape and the technical difficulties of using such material were resolved in a research project carried out in the late 1980ís. Developments in photogrammetry since then, allow very dense spatial data to be acquired (1m resolution) in the form of digital elevation models. It is also possible to generate ortho-photographs which appear to look like the original aerial photograph but are actually maps. Spatial data representing the site at different epochs since 1946 include: 1958, 1969, 1976, 1988, 1995, 2000 and 2001.
Using this type of material it has been possible to accurately quantify the changes that have occurred.
It has also been possible to animate the changes that
have occurred on Black Ven, which you are encouraged to view either on this interactive display or later via the Charmouth Heritage Coast Centre
website (www.charmouth.org). These allow
the dramatic changes to be visualised in a novel way and it is equally
surprising to detect adjacent areas exhibiting both stability and instability!
Key animations include: