The Cribarth Disturbance is a geological structure forming a

lineament ''See also Line (geometry)'' A lineament is a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will appear as a fault-aligned valley, a series of fault or fold-align ...

which stretches across south

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

from

Swansea Swansea ( ; ) is a coastal City status in the United Kingdom, city and the List of urban areas in the United Kingdom, second-largest city of Wales. It forms a Principal areas of Wales, principal area, officially known as the City and County of ...

up the

Swansea Valley The Swansea Valley (; ) is one of the South Wales Valleys. It is the valley from the Brecon Beacons National Park to the sea at Swansea of the River Tawe in Wales. Administration of the area is divided between the City and County of Swansea, Nea ...

then northeastwards to

Brecon Brecon (; ; ), 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 county town of Breck ...

and beyond. It consists of both a series of faults and associated folds which were active during the mountain-building period known as the

Variscan orogeny The Variscan orogeny, 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 ''Varis ...

. This line of weakness probably featured in the earlier

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

and perhaps reflects a more ancient line of weakness in the

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

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

, 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 Gre ...

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

Abercraf Abercraf (also ; or Abercrave) is a village in Powys, Wales, in the community of Ystradgynlais and within the historic boundaries of the county of Brecknockshire. A distinct dialect of English is spoken in the village, as well as the Welsh lang ...

and Swansea. It is now occupied by the

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

. The geologically complex mountain of

Cribarth Cribarth (nicknamed the ''Sleeping Giant'') is a hill in the Brecon Beacons National Park, Powys, Wales, in the traditional county of Brecknockshire. The summit lies on the broken ridge at an elevation of at OS grid reference SN 831143. To its ...

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 (; ) existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). It was in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalon ...

in the middle Palaeozoic Era and giving rise to the Caledonian Orogeny or mountain-building period. The Neath Disturbance and the Carreg Cennen Disturbance are similar features also found in south Wales. The Bala Fault,

Menai Strait The Menai Strait () is a strait which separates the island of Anglesey from Gwynedd, on the mainland of Wales. It is situated between Caernarfon Bay in the south-west and Conwy Bay in the north-east, which are both inlets of the Irish Sea. The s ...

Fault,

Southern Uplands Fault The Southern Uplands Fault (or occasionally Southern Upland Fault) is a fault in Scotland that runs from Girvan (or more specifically from the Rhins of Galloway) to Dunbar on the East coast. It marks the southern boundary of the Scottish Midla ...

Highland Boundary Fault The Highland Boundary Fault is a major fault zone that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east. It separates two different geological terranes which give rise to two distinct physiographic ter ...

and

Great Glen Fault The Great Glen Fault is a strike-slip fault that runs through the Great Glen in Scotland. Occasional moderate tremors have been recorded over the past 150 years. Location Aligned northeast to southwest, the Great Glen Fault extends further sout ...

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