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Wicken Water Boulders, ARKESDEN, Uttlesford District, TL48203449, Potential Local Geological Site

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Site name: Wicken Water Boulders.

Grid reference: TL 4820 3449

Brief description of site:

A large number of large erratic boulders situated in the bed of the stream (Wicken Water) by the road bridge in the centre of Arkesden village. The stream bed is usually dry, and thus the stones are safe to visit provided care is taken when traversing the stream bed.

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Details

A large concentration of boulders can be seen in the bed of the Wicken Water, a stream running through Arkesden village. They are by the road bridge (near the village hall) and consist of boulders of Hertfordshire puddingstone and sarsen stones. There are at least 12 boulders here, of varying sizes and shapes, the largest boulder being a slab of colourful puddingstone 1.5 metres by 1.1 metres in size. Most of the stones are obscured by silt from the stream or covered in moss. One rounded boulder of puddingstone has been cleaned to reveal its colour and texture. A sarsen stone is present at each end of the bridge itself.

Hertfordshire puddingstone it contains well-rounded flint pebbles bound together with quartz ‘cement’, making it a very tough rock. Sarsen stones are boulders of extremely hard sandstone. They are distinctly different rocks but were both formed under the same conditions around 55 million years ago when the climate of Britain was very hot. Both rocks are very resistant to erosion. The formation of silcretes (which include puddingstone and sarsens) has been the subject of recent scientific debate. Research has compared the conditions under which puddingstones and sarsens were formed with the present day climate in the Kalahari Desert and parts of Australia.

Arkesden is unique in Essex for the number of erratic boulders that are scattered around the village. They can also be seen on the roadside, by the inn, and in private gardens.

The boulders of puddingstone that are found in Essex most probably originated in Hertfordshire and were brought to Essex by the Thames when it flowed far to the north of its present course. Sarsens are thought to have been brought into Essex from the chalk hills to the north by ice. However, the large number of stones in the stream bed here raises the intriguing possibility that there might have once been a more local source (Lucy 2015). Such boulders are usually concentrated in river valleys as they have slowly moved downhill under gravity during the ice age.

One of the large sarsens in the stream bed has a circular hole which may be a pothole formed by a torrent of meltwater beneath the ice sheet. This near circular hole, with its distinctive spiral and sudden constriction half way down, is typical of a pot-hole drilled out by hard pebbles caught up in turbulent high pressure water (Howgate 2018). .

The boulders are situated beneath the road bridge, which was opened in 1911, and are found at the apex of a hairpin bend in the stream. It is not known whether this location is significant. A.E. Salter, in his 1914 paper, refers to the stones in the stream bed here.



The Wicken Water Boulders on the occasion of the Geologists' Association visit in 2015. The 'pothole' can be seen in the foreground. Photo: G.Lucy

 

Wicken Water sarsen pothole
Wicken Water sarsen pothole

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Reference: Salter 1914, Lucy 2015, Howgate 2018.

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