Geology Site Account

Site name: Greenfields Pingo

Grid reference: TL 6841 2277

Brief description of site:

Site of a possible Ice Age pingo discovered by archaeologists while excavating in advance of the new A120 road between Stansted Airport and Braintree.

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Details

In 2001 archaeologists working on the site of the proposed A120 road between Stansted Airport and Braintree discovered evidence of middle Bronze Age (and later) activity centred around a large hollow up to 20 metres (60 feet) in diameter and almost 2 metres (6 feet) deep. The hollow had the appearance of the remains of a glacial pingo. If this is the case it must have been a feature in the landscape for tens of thousands of years by the time middle Bronze Age settlers discovered it some 4,000 years ago. The archaeologists took two samples through the fills of the hollow which revealed sparse pollen but unfortunately this was not further analysed. A significant quantity of middle Bronze age pottery was recovered from the hollow as well as over 500 fragments of clay moulds used in Bronze metal working. Use of this natural feature, which was probably a shallow lake, appears to have continued through to the Iron Age and possibly the Roman period, suggesting it might have acted as a sacred place before eventually becoming infilled.

If the Greenfields hollow is a scar left behind by the melting of a pingo, it must date from the last glacial stage some 20,000 years ago. Pingos are massive bodies of ground ice that grow by drawing water from unfrozen ground beneath the permafrost, the influx of water from below usually leads to bulging of the underlying strata but this has not been reported at Greenfields. At the end of the glacial stage, melting of the pingo results in the collapse of overlying deposits into the hole left by the melting ice.

Pingos exist in Arctic areas today such as north-west Canada, giving us a vivid reminder of conditions that existed in Essex valley during the most recent glacial stage, the Devensian, when an ice sheet extended across Britain as far south as Norfolk.

The site is now beneath the new road.