Geology Site Account

Site name: Holland-on-Sea Cliff SSSI

Grid reference: TM 211166

Brief description of site:

Summary

Site of Special Scientific Interest designated for the importance of its geology. The gravel in the cliff at Holland-on-Sea dates from just before and just after the Thames was diverted and therefore is important for research into the evolution of the Thames and its tributaries during the Ice Age.

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Site description

About 450,000 years ago a catastrophic change affected the Thames causing it to alter its course and adopt the route we know today. The gravel in the cliff at Holland-on-Sea dates from just before and just after the Thames was diverted (Lower Holland Gravel and Upper Holland Gravel). The stone content of the Lower Gravel is typically of a mixture of stone types from the early Thames and the Medway, indicating that this area was the confluence of the two rivers. The Upper Gravel includes Rhaxella chert brought in by meltwater streams from the Anglian ice sheet. The deposits reveal just how rapid the diversion was as the Thames suddenly ceased to flow through central Essex as a result of being blocked upstream between Hertfordshire and Colchester by the Anglian ice sheet. Gravel of the same age is present in St. Osyth Gravel Pit. St. Osyth lies upstream from the confluence with the Thames and Medway rivers whereas Holland-on-Sea lies within the area of the confluence.

The cliffs have been landscaped and no gravel is now visible. However, in late 2018 cliff protection works provided temporary exposures and the opportunity for sections in the gravel to be studied again.

Section in the Upper Holland Gravel revealed during cliff protection works in November 2018