Editing Cheddar Gorge (section)

== Geology ==
[[File:cheddar gorge from aircraft arp.jpg|thumb|alt=Looking down into the gorge with a road with cars on it running from the top to the bottom of the picture. To the left are less steep slopes covered in vegetation.|Aerial photograph, showing the cliff faces to the south (right hand side of picture) and the slopes to the north]]
Cheddar Gorge is located  on the southern edge of the [[Mendip Hills]],<ref name="naturescalendar">{{cite web|url=https://www.bbc.co.uk/naturescalendar/summer/honeypots/cheddar/cheddar_gorge.shtml|title=Tourist hotspots&nbsp;– Cheddar Gorge|work=Natures Calendar|publisher=BBC|access-date=10 September 2008|url-status=live|archive-url=https://web.archive.org/web/20081216135459/http://www.bbc.co.uk/naturescalendar/summer/honeypots/cheddar/cheddar_gorge.shtml|archive-date=16 December 2008}}</ref> with a  maximum depth of  {{convert|137|m|ft|0|abbr=on}},<ref>{{cite web|url=http://www.iknow-somerset.co.uk/tourist_information/central_somerset/cheddar/cheddar_gorge_showcaves.htm|title=Cheddar Gorge and Caves Jacobs Ladder Tourist Information|url-status=dead|archive-url=https://web.archive.org/web/20090605224323/http://www.iknow-somerset.co.uk/tourist_information/central_somerset/cheddar/cheddar_gorge_showcaves.htm|archive-date=5 June 2009|access-date=10 August 2009}}</ref><ref>{{cite web|url=https://www.bbc.co.uk/somerset/content/articles/2008/10/20/cheddar_gorge_feature.shtml|title=Cheddar Gorge and Caves: the natural wonder home to everyone|url-status=live|archive-url=https://web.archive.org/web/20110502151807/http://www.bbc.co.uk/somerset/content/articles/2008/10/20/cheddar_gorge_feature.shtml|archive-date=2 May 2011}}</ref> a near-vertical cliff-face to the south, and steep grassy slopes to the north. The [[B roads in Zone 3 of the Great Britain numbering scheme|B3135 road]] runs along the bottom of the Gorge.

The area is underlain by Black Rock [[slate]], Burrington [[Oolite]] and [[Clifton Down Limestone]] of the [[Carboniferous]] [[Limestone]] Series, which contain [[Oolite|ooliths]] and fossil debris, on top of [[Old Red Sandstone]] and by [[Dolomite (rock)|dolomitic]] [[Conglomerate (geology)|conglomerate]] of the [[Keuper]]. Evidence for [[Variscan orogeny]] is seen in the sheared rock and cleaved [[shale]]s. In many places weathering of these [[Stratum|strata]] has resulted in the formation of immature [[calcareous]] soils.<ref name="sssi" />

The gorge was originally formed 225 million years ago, during the [[Triassic Period]], when the [[Mendip Hills|Mendip]] [[Carboniferous Limestone|Carboniferous limestone]] stood as a series of  "[[Roche moutonnée|whalebacked]]" hills.  At that time Britain had a warm [[Desert climate|arid climate]], not dissimilar to [[North Africa|northern Africa]] today. Occasionally [[flash flood]]s cause huge volumes of water to run off the hills, forming ''[[wadi]]s'' — an Arabic term for the steep-sided [[ravine]]s characteristic of intermittent streams. Cheddar Gorge and its near neighbour, [[Burrington Combe]], are [[Exhumation (geology)|exhumed]] ''wadis''. They were originally filled with Triassic rocks that may have been eroded out by [[Meltwater|glacial meltwaters]] at the end of the last [[Ice age|Ice Age]]. Parts of Burrington Combe still have these Triassic rocks, forming an [[unconformity]] with the Carboniferous limestones along their sides and bottom.

During the Ice Ages, [[permafrost]] blocked the caves with ice and frozen mud, making the limestone impermeable. When this melted during the summers, water was forced to flow on the surface,  carving out the softer Triassic rocks, exhuming the ''wadi''.<ref>{{cite web|url=http://www.bgs.ac.uk/mendips/localities/cheddar.html|title=Cheddar Gorge|publisher=British Geological Survey|access-date=10 September 2008|url-status=live|archive-url=https://web.archive.org/web/20081216141100/http://www.bgs.ac.uk/mendips/localities/cheddar.html|archive-date=16 December 2008}}</ref> During warmer periods, the water flowed underground through the [[Permeability (fluid)|permeable]] limestone, creating the caves and leaving the gorge dry, so that today much of the gorge has no river until the underground [[Cheddar Yeo]] river emerges in the lower part from [[Gough's Cave]]. The river is used by [[Bristol Water]], which  maintains a series of dams and ponds  supplying  the nearby [[Cheddar Reservoir]],<ref>{{cite web | url= http://www.bristol-water.co.uk/pdf/environment/w2008/WRP%202010%20v1.1%20D%20REP.pdf | title= Draft Water Resource Plan | pages= 21 | publisher= [[Bristol Water]] | date= 18 April 2008 | access-date= 10 September 2008 | url-status= dead | archive-url= https://web.archive.org/web/20090319215844/http://www.bristol-water.co.uk/pdf/environment/w2008/WRP%202010%20v1.1%20D%20REP.pdf | archive-date= 19 March 2009}}</ref><ref>{{cite web|url=http://www.bristolwater.co.uk/leisure/cheddar-info.asp |publisher=[[Bristol Water]] | title=Cheddar Reservoir Introduction |access-date=10 September 2008 |url-status=dead |archive-url=https://web.archive.org/web/20100325204405/http://www.bristolwater.co.uk/leisure/cheddar-info.asp |archive-date=25 March 2010 }}</ref> via a {{convert|137|cm|in|0|adj=on}} diameter pipe that takes water just upstream of the [[Rotary International|Rotary Club]] [[Sensory garden|Sensory Garden]], a [[Urban park|public park]] in the Gorge opposite Jacob's Ladder.

The gorge is susceptible to flooding. In the [[Chew Stoke flood of 1968]], the flow of water washed large boulders down the gorge, damaging the café, the entrance to Gough's Cave<ref>{{cite news|title=40 years since the Great Gorge Flood|url=http://www.thewestonmercury.co.uk/news/40_years_since_the_great_gorge_flood_1_321776|access-date=24 February 2011|newspaper=Western Mercury|date=10 July 2008|url-status=live|archive-url=https://web.archive.org/web/20110929011254/http://www.thewestonmercury.co.uk/news/40_years_since_the_great_gorge_flood_1_321776|archive-date=29 September 2011}}</ref> and washing away cars.<ref>{{cite web|title=The Chew Valley floods of 1968|url=http://www.publow-with-pensford-pc.gov.uk/pub/backlook/env_agency_leaflet.pdf|publisher=Environment Agency|access-date=24 February 2011|url-status=live|archive-url=https://web.archive.org/web/20110716144901/http://www.publow-with-pensford-pc.gov.uk/pub/backlook/env_agency_leaflet.pdf|archive-date=16 July 2011}}</ref> In the cave itself, the flooding lasted for three days.<ref>{{cite journal|last=Donovan|first=D.T.|title=Gough's Cave, Cheddar, Somerset. Quaternary Stratigraphy|journal=Proceedings of the University of Bristol Spelæological Society|year=2006|volume=24|issue=1|pages=17–35|url=http://www.ubss.org.uk/resources/proceedings/vol24/UBSS_Proc_24_1_17-35.pdf|access-date=24 February 2011|url-status=live|archive-url=https://web.archive.org/web/20110721000148/http://www.ubss.org.uk/resources/proceedings/vol24/UBSS_Proc_24_1_17-35.pdf|archive-date=21 July 2011}}</ref> In 2012 the [[B3130 road|B3135]] road through Cheddar Gorge was closed for several weeks following damage to the road surface as a result of extensive flooding.<ref>{{cite web | url=http://www.thisissomerset.co.uk/Cheddar-Gorge-road-remains-closed-following/story-17514991-detail/story.html | title=Cheddar Gorge road remains closed following floods | publisher=This is Somerset | access-date=18 December 2012|archive-url=https://web.archive.org/web/20150611094323/http://www.westerndailypress.co.uk/Cheddar-Gorge-road-remains-closed-following/story-17514991-detail/story.html|archive-date=11 June 2015 }}</ref><ref>{{cite news | url=https://www.bbc.co.uk/news/uk-england-somerset-20637358 | title=Flood-hit Cheddar Gorge road to remain closed | publisher=BBC | access-date=18 December 2012 | date=7 December 2012 | url-status=live | archive-url=https://web.archive.org/web/20121210070457/http://www.bbc.co.uk/news/uk-england-somerset-20637358 | archive-date=10 December 2012}}</ref>