Bourne SSSI, Avon () is an 8.47

hectare The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm2), that is, square metres (), and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. ...

geological Site of Special Scientific Interest A Site of Special Scientific Interest (SSSI) in Great Britain, or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland, is a conservation designation denoting a protected area in the United Kingdom and Isle ...

near the village of Burrington,

North Somerset North Somerset is a unitary authorities of England, unitary authority in the ceremonial county of Somerset, England. The council is based in Weston-super-Mare, the area's largest town. The district also contains the towns of Clevedon, Nailsea ...

, notified in 1992. This site is of considerable importance because it has provided detailed information upon the composition of a north Mendip

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to Semi-arid climate, semiar ...

. An alluvial fan is a fan-shaped deposit formed where a fast flowing

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...

flattens, slows, and spreads typically at the exit of a

canyon A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency t ...

onto a flatter

plain In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and ...

. At Bourne sections have shown highly weathered gravels overlain by sandy silts and clay loams, the highest levels in the sequence showing evidence of

cryoturbation In gelisols (permafrost soils), cryoturbation (frost churning) refers to the mixing of materials from various horizons of the soil down to the bedrock due to freezing and thawing. Cryoturbation occurs to varying degrees in most gelisols. The cau ...

. Two phases of fan sediment deposition were separated by a long period of subaerial weathering, which may represent an interglacial period.English Nature citation sheet for the site
(accessed 9 July 2006)

References

{{SSSIs Avon geological Sites of Special Scientific Interest in Avon Sites of Special Scientific Interest notified in 1992