Geology Site Account

Site name: Wouldham Cliff (Involutions)

Grid reference: TQ 6013 7936

Brief description of site:

Rare periglacial features can be seen in the low section of cliff adjacent to Merlin Close. Part of Chafford Gorges Nature Park. Geological interest is easily obscured by the growth of vegetation and should be controlled.

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Summary of geological interest

At the north end of Wouldham Cliff is clear evidence of the climate that existed in Essex to-wards the end of the last glacial stage, between 10,000 and 20,000 years ago, when the ground was permanently frozen (permafrost) with only the top metre or so thawing during each brief summer and freezing again in the autumn. Where the Chalk was close to the surface this process turned the top layer of chalk into a mass of saturated chalk rubble which is now known as coombe rock (this type of rock is well displayed in Warren Pit - see separate site record).

Here at Wouldham Cliff a thin layer of Thanet Sand overlies the Chalk and in places it has sunk into the shattered chalk creating curious festoon-like structures. Scientists know how these structures, called involutions, have been formed because the same processes are going on in the arctic today. At the end of the period of permafrost the ground thawed out completely and the saturated sand was too heavy for the shattered and equally saturated chalk to bear and the sand slowly sank into the chalk. Visible here and there are not only rounded masses of sunken sand but also mushroom-shaped masses of chalk injected upwards as it was displaced. Further proof that these structures were formed in this way is the fact that they are only seen where the Thanet Sand is thin, indicating that the patterns must have formed close to the ground surface at that time.

This cliff section forms part of Chafford Gorges Nature Park and is managed by the Essex Wildlife Trust.

Evidence of an extremely cold climate in the form of involutions at the north end of Wouldham Cliff. Photo © G. Lucy.