Geology Site Account

Site name: Blackweir Pond, Epping Forest

Grid reference: TQ 423 978

Brief description of site:

Blackweir Pond is a picturesque pond in Epping Forest that was originally a gravel pit. The gravel here is glacial moraine left behind by an ice sheet which surrounded the Epping Forest ridge during the coldest part of the Ice Age.

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Details

About 450,000 years ago the Anglian ice sheet reached its maximum southerly extent across the British Isles and the high ground of the Epping Forest ridge was surrounded by ice. As the glaciers melted they dumped great quantities of material, known as glacial moraine, at their margins. These mounds are called kames, or more accurately kame terraces, and one of these is preserved as a patch of gravel nearly a kilometre long that follows the contour of the valley south of Great Monk Wood. The geological map shows this as Woodford Gravel (an ancient river gravel) but this is clearly not the case.

Early twentieth century accounts by the Essex Field Club of visits to a gravel pit here (Thompson 1913 & Warren 1910) record that the gravel contains much exotic material such as rhaxella chert which originates in the north of England, thereby confirming that it is not river gravel but is derived from a melting glacier. The pit in question is now Blackweir Pond, which has been described as the most picturesque of all the Forest ponds.

Further research

A lot of gravel is still visible in the banks of the Blackweir Pond such as on the west shore (TQ 4227 9784). Sampling of the gravel for analysis could best be carried out at a spot south-west of the pond on a steep bank (TQ 4227 9777) where a small section through the gravel could be created with the permission of Natural England and the Epping Forest Management Team.

Blackweir Pond in Epping Forest. Photo: G.Lucy