Avon Gorge

The Avon Gorge () is a 2.5km (1.5mi) long gorge on the River Avon in Bristol, South West England. The gorge runs south to north through a limestone ridge 2km west of Bristol city centre and about 5km from the mouth of the river at Avonmouth. The gorge forms the boundary between the unitary authorities of North Somerset and Bristol. In the past, when Bristol was an important port, the gorge formed a spectacular defensive gateway to the city.

On the east of the gorge is the town of Clifton, part of Bristol city, and The Downs, a large public park. To the west of the gorge is Leigh Woods, the name of both a village and the National Trust forest it is situated in. There are three Iron Age hill forts overlooking the gorge, as well as a more recent observatory. The Clifton Suspension Bridge, an icon of Bristol, crosses the gorge.

Geology and formation

The gorge cuts through a ridge mainly of limestone, with some sandstone. This particular ridge runs from Clifton to Clevedon, ten miles away on the Bristol Channel coast, though limestone is found throughout the Bristol area. The fossil shells and corals indicate that the limestone formed in shallow tropical seas in the Carboniferous, 350 million years ago. For a long time it was unclear what caused the Avon to cut through the limestone ridge, rather than run south west through the Ashton Vale towards Weston-super-Mare. However, Bristol was at the southern edge of glaciation during the last ice age, and it has been suggested that ice blocked the Ashton Vale,River Avon Trail, "Avon Gorge." Accessed 2006-05-05. or a glacier carved the gorge.Vicki Buckley and Alex Perry, 1999. Local Geology Weekend. Accessed 2006-05-05.

At various times the sides of the gorge have been quarried, leaving steep gorge walls. In the 18th century the gorge was quarried to produce building stone for the city. Stone was taken by boat into the floating harbour. In the 19th century celestite was discovered in Leigh Court estate, and the Wills family authorised quarrying. Between 1880 and 1920 Bristol was producing 90% of the world's celestite, but the enterprise did not last long into the 20th centuryC.G. Down, 1968. "Paradise Bottom." The Industrial Railway Record No. 22 - p352-354. Quarries on the Bristol side of the gorge are now popular with climbers and are a habitat for Peregrine falcons and other wildlife.

Ecology

The steep walls of the gorge support some rare fauna and flora, including species unique to the gorge. There are a total of 24 rare plant species and two unique trees: the Bristol and Wilmotts's whitebeams.BBC Bristol, "The Avon Gorge - Bristol's Great Glacier?" Accessed 2006-05-05. Other notable plants include Bristol rock cress, Bristol onion, Spiked Speedwell, Autumn Squill and Honewort. Because of its steep sides, there are many parts of the gorge on which trees can not grow, making way for smaller plants. The gorge is also home to many rare invertebrate species.Avon Wildlife Trust, "The wildlife and habitats of Avon." Accessed 2006-05-05. The gorge has a unique microclimate, around 1 degree warmer than the surrounding land. The steep south-west facing sides receive the afternoon sunlight, but are partially sheltered from the prevailing winds. When winds come from the Bristol Channel in the north west they may be funnelled into the gorge, creating harsh and wet conditions.

The steep gorge walls make an ideal habitat for peregrine falcons, with a plentiful suply of food nearby in the form of pigeons and sea gulls. Peregrines have a history of nesting in the gorge, but having become rare in the British Isles they did not breed and were rarely seen in the gorge after the 1930s. In 1990 Peregrines returned to the gorge, and have successfully bred in most of the following years.Bristol Ornithological Club, "Peregrine Falcon History In The Avon Gorge." Accessed 2006-05-05. On warm days a strong uplift forms in the gorge, on which birds of prey soar while hunting. The gorge also houses large populations of Jackdaw and horseshoe bats, both of which find homes in the caves and bridge buttresses.

Due to its geology and ecology, an area of 155.4 hectares of the gorge and surrounding woodland has been protected as a biological and geological Site of Special Scientific Interest (SSSI), the original notification taking place in 1952. The site may in future be protected as a Special Area of Conservation under the European Habitats Directive. The Leigh Woods side of the gorge is largely owned by the National Trust. The Downs on the city side of the gorge are owned by Bristol City Council and managed as a large public park. The actual gorge side is protected in partnership with Bristol Zoo, WWF and English Nature. The council's management of the gorge involves balancing the need to protect its ecology with recreational uses such as rock climbing.

History of human use

The gorge area was inhabited at least as early as the iron age, probably by the Dobunni tribe. In Leigh Woods above Nightingale Valley, a steep dry valley beside the suspension bridge, is Stokeleigh Camp, one of three iron age hill forts in the area. Stokeleigh was occupied from 3BCE to 1CE, and was also used in the middle ages. The camp was protected on two sides by the cliff faces of the gorge and Nightingale Valley, and was also protected by earthworks, and is now a scheduled ancient monument. A second hill fort was situated across Nightingale Valley, but has since been built on, and bridge road cuts through it. The third hill fort was situated on the opposite side of the gorge, in what is now observatory green. Archaeology, plus the configuration of the three forts, suggest they played a role in defending the gorge.

During the middle ages and industrial revolution the area which now forms The Downs was used as common grazing land, was mined for lead, calamine, iron and limestone, and became home to a windmill which produced snuff from the tobacco which had become one of the city's principal imports. In 1777 the windmill bunt out in a storm, and the building was converted into the observatory, which houses a camera obscura. In the 18th and 19th centuries Bristol's economy boomed and Clifton became a desirable place to live. Mansion houses were built over looking the gorge, but after grazing was stopped, trees grew and obscured the view from these mansions. In the Victorian era, with houses creeping further onto the Downs, an Act of Parliament was passed to protect them as a park for the people of Bristol. In 1754 a bridge to span the gorge was proposed, but it was nearly 80 years before work began on Isambard Kingdom Brunel's Clifton Suspension Bridge, and a further 30 years of delays before it was completed. Today the bridge is perhaps the best known landmark in Bristol.

Throughout Bristol's history the gorge has been an important transport route. It is the gateway to Bristol Harbour, and provided protection against storms or attack. The Bristol Channel and Avon estuary have a very high tidal range, and the gorge is relatively narrow and meandering, making it notoriously difficult to navigate and giving rise to the phrase ship shape and Bristol fashion.

Today Bristol Harbour is no longer an important port, but the gorge is still a transport route. The A4 road runs through the gorge, linking Bristol city centre to the M5 motorway, which bypasses the city near Avonmouth. Two railways run through the gorge, on the east side the passenger railway to Avonmouth and Severn Beach runs through part of the gorge, and through a tunnel under the Downs, while on the west side is the former Portishead Railway, which was closed by the Beeching Axe in the 1960s, but has now been reopened for freight traffic as far as Royal Portbury Dock, 4km (2.5mi) downstream. Between 1893 and 1934, the Clifton Rocks Railway linked the passenger steamer pier at Hotwells with Clifton on the rim of the gorge.

A footpath and National Cycle Network cycleway run alongside the Portishead Railway and along the old towpath.

Mythology

The formation of the Avon Gorge is the subject of mediaeval mythology. The myths tell tales of two giant brothers, Vincent and Goram, who constructed the gorge. One variation holds that Vincent and Goram were constructing the gorge together and Goram fell asleep, to be accidentally killed by Vincent's pickaxe. Another variation tells of the brothers falling for Avona, a girl from Wiltshire, who instructs the giants to drain a lake which stretches from Rownham Hill to Bradford-on-Avon (i.e. the Avon valley). Goram began digging the nearby Hazel Brook Gorge in Blaise Castle estate, but consumed too much beer and fell asleep. Vincent dug the Avon Gorge and drained the lake, winning the affection of Avona. Upon waking Goram stamped his foot, creating "Goram's Chair" in the Blaise Castle estate, and threw himself into the Bristol Channel, turning to stone and leaving head and shoulder above water as the islands Flat Holm and Steep Holm.Eugene Byrne & Simon Gurr, 2002. "Bristol Myths and Legends." Bristol 2008: St Vincent's Rock.

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