The Cribarth Disturbance is a geological structure forming a lineament which stretches across south

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

from Swansea up the Swansea Valley then northeastwards to

Brecon Brecon (; cy, Aberhonddu; ), archaically known as Brecknock, is a market town in Powys, mid Wales. In 1841, it had a population of 5,701. The population in 2001 was 7,901, increasing to 8,250 at the 2011 census. Historically it was the coun ...

and beyond. It consists of both a series of faults and associated

fold Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure *Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Above ...

s which were active during the mountain-building period known as the

Variscan orogeny The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Variscan'', comes ...

. This line of weakness probably featured in the earlier

Caledonian Orogeny The Caledonian orogeny was a mountain-building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that oc ...

and perhaps reflects a more ancient line of weakness in the

basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the Furnace (house heating), furnace, ...

rocks. It is also known (in part) as the Tawe Valley Disturbance or the Swansea Valley Disturbance.

Influence on the landscape

The Disturbance is responsible for a number of significant landscape features along its 50 km length. Prominent amongst these is the Swansea Valley, formed both by glacial action during the

ice ages An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gree ...

and river erosion along this line of weakness in the Earth's crust between

Abercraf Abercraf ( en, Abercrave) is a village within the historic boundaries of the county of Brecknockshire, Wales, administered as part of the unitary authority of Powys, and in the community of Ystradgynlais. Between 1965 and 1991, the village was th ...

and Swansea. It is now occupied by the

River Tawe The River Tawe (; cy, Afon Tawe ) is a long river in South Wales. Its headwaters flow initially east from its source below Llyn y Fan Fawr south of Moel Feity in the Black Mountains, the westernmost range of the Brecon Beacons National P ...

. The geologically complex mountain of Cribarth also lies on the Disturbance and indeed gives its name to the feature.

The Caledonian Orogeny

The Cribarth Disturbance is one of the southernmost geological features within Britain which can be described as following the Caledonoid trend. The phrase describes a suite of major northeast-southwest oriented geological structures associated with the closure of the former

Iapetus Ocean The Iapetus Ocean (; ) was an ocean that existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). The Iapetus Ocean was situated in the southern hemisphere, between the paleoc ...

in the middle

Palaeozoic Era The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and '' ...

and giving rise to the Caledonian Orogeny or mountain-building period. The

Neath Disturbance The Neath Disturbance is a geological structure which stretches across south Wales from Swansea Bay northeastwards as far as Hereford in western England. It consists of a series of both faults and associated folds which were active during the mou ...

and the

Carreg Cennen Disturbance The Carreg Cennen Disturbance is a zone of geological faults and folds in south and mid Wales which forms a part of both the Church Stretton Fault Zone and the Welsh Borderland Fault System. To the southwest it is known as the 'Llandyfaelog Dis ...

are similar features also found in south Wales. The Bala Fault, Menai Strait Fault, Southern Uplands Fault, Highland Boundary Fault and Great Glen Fault are other major Caledonoid structures of Britain.Woodcock, W. & Strachan, R. 2000 'Geological History of Britain and Ireland' Blackwell Science (publishers), Cambridge

References

{{Reflist Geology of Wales