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| Dorset and East Devon Coast World Heritage Monitoring |
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| GCR Site: 1321 Black Ven |
| Interest: Landslides |
| GCR Block: Mass Movement |
| SSSI: West Dorset Coast |
| Site Boundaries: Grid Reference 334700, 92700 - 336300, 93100 |
| Date of Assessment: N/A - Trial |
| Date from last assessment: N/A |
| Name of surveyor: Richard Edmonds |
| Statement of Significance: |
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This is a complex and active multiple landslip, Cretaceous Chert Beds, Upper Greensand and Gault (here a sandy silt) have slipped seaward over impermeable Lower lias clays, on which the Gault lies unconformably. There is a slight south-eastward dip, with a seaward component. There is much local faulting and flexure, and a partly eroded syncline within the cliff serves to localise the discharge of ground water. The site is important for its demonstration of movement in arenaceous flows of cohesionless remoulded material due to copious water supply from the Cretaceous strata. The addition of more water supplies as flows progress downslope ensures that they reach the beach at the foot of the cliff. This deprives the upper part of the cliff of its toe, creating conditions for further failure. A classic much studied landslip. |
| Physical description: |
| Black Ven extends from Lyme Regis in the west (also known as the Spittles) through to Charmouth in the east and consists of a series of terraced cliffs terminating in a steep sandstone cliff top. |
| Health and Safety: |
| Obviously a dangerous site with mudflows and quicksands (satturated Upper Greensand slides) in winter or after wet weather, terraces, cliffs and hidden fissures. The cliffs are prone to cliff falls at any time. The tide floods the beach shortly after low tide by the groynes at East Cliff, Lyme Regis. |
| Access: |
| The best access along the beach from Charmouth. There is no access from the cliff top or from the Spittles (informal paths require local knowledge). Note the tidal problems stated above. |
| Conservation Objectives, on site: |
| Ensure
that natural coastal processes continue Maintain 'naturalness' of the site |
| Conservation Objectives, off site: |
| Record landslide events |
| Success indicators: |
| Natural processes continue and are recorded |
| Fixed Point photography: |
| Panoramic
view from the rock boulders on the foreshore at (at low tide) GRSY355928 From the National Trust field, Charmouth GRSY356934 From Long Entry, Lyme Regis GRSY345923 |
| Scientific publications and ongoing research: |
| The Lyme
Bay and South Devon Coastal Group are considering establishing a long
term coastal monitoring project similar to the Channel Coast Observatory
and including the use of aerial photography. Jim Chandler from Loughborough University has developed a long term analysis of erosion rates at Black Ven The Charmouth Heritage Coast Centre has been running a Black Ven Bio-diversity Project which includes work on erosion processes and events. West Dorset District Council have commissioned a detailed stratigraphical study and mapping project with regard to the relationship between the hard strata and landslide benches extending into the town. |
| Natural Change: |
| An active site with significant recent movement, especially in the west around the Spittles |
| Man made change: |
| West Dorset District Council are considering new engineering for East Cliff, Lyme Regis |
| ENSIS unit summary: |
| Unknown - trial |
| Comments: |
| Other comments: |
| Sensitivity: |
| Low |
| Recommended survey period: every 3 years |
| Overall Assessment: |
| Favourable |
| Actions: |
| Record
landslide events monitor the success of the West Dorset Fossil Collecting code o conduct in reducing diggin in the cliffs (see GCR 87) Ensure that the interest of the site is incorporated into the next Shoreline Management Plan Work with the Lyme Bay and South Dorset Coastal Group (Engineers) to promote a coastal monitoring programme similar to the Channel Coast Observatory (Portland east to Selsey Bill) |
| Related GCR Blocks: |
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GCR
87 Pinhay
Bay to Fault Corner Lower Jurassic Stratigraphy GCR 2109 Golden Cap - Lyme Regis Coastal Geomorphology of England
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Comments
and discussion
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No comments submitted
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