Over the last few years we have noticed that some of the wave cut platforms along Monmouth Beach west of Lyme Regis have been breaking and even bursting out of the shore platforms. The most spectacular event took place over the last two weeks of July 2011 when an area 8 m by 3m lifted up and broke open. Since then several other observations have been made of smaller but deeper failures in different beds across the platforms, some dating from 2011 but others that are clearly older running along the sides of displacements within the platforms.
Natural England has provided a grant to undertake detailed survey work of this process, the purpose being to create a very detailed baseline of the ledges against which we can see how they are breaking up and eroding. This is a particularly unusual process that may not have been described in the scientific literature before and we do not as yet understand what mechanism may be at work.
The survey involved an Unmanned Aerial vehicle (UAV) operated by Suave Aerial Photographers based in Preston Lancs. A remote controlled helicopter was used as a platform to carry a professional digital SLR camera over the ledges to create a photographic mosaic of images at very high resolution. An area approximately 250 m by 30 m was photographed at 12 mm resolution (each pixel on the screen being that size on the ground) while more detailed surveys were taken at just 2 mm resolution, enabling small features in the surface of the platform to be recorded.
Part of the ammonite pavement high res survey with inset, a sample at the highest resolution
The results are stunning, if a little abstract to someone not familiar with the area. It provides a totally new perspective from that obtained on the ground and the intention now is to use that baseline to measure future change. However, it will also be possible to use the survey to see how the ledges have evolved in the past. William Lang retired to Charmouth from the Natural History Museum and in the 1930’s he mapped each of the individual ledges along the foreshore east and west of Lyme. We can now compare his map with what is there today and from that obtain a very accurate measure of how the ledges have responded to 80 years of erosion. Early analysis indicates that the ledges have lowered by as much as 2 m in places and that the overall pattern of erosion is from the east to the west.
The results will be placed on line at some stage in the neat future, probably using Dorset Explorer, the county councils GIS and mapping system but that will take some time. The survey is just the start of the process and further studies and surveys are planned but the problem with this kind of work is that it is subject to nature’s change and we cannot predict what that may be so watch this space!
Richard Edmonds, Earth Science Manager