Cribarth Disturbance
Encyclopedia
The Cribarth Disturbance is a geological structure forming a lineament
which stretches across south Wales
from Swansea
up the Swansea Valley
then northeastwards to Brecon
and beyond. It comprises both a series of faults and associated fold
s which were active during the mountain-building period known as the Variscan orogeny
. This line of weakness probably featured in the earlier Caledonian Orogeny
and perhaps reflects a more ancient line of weakness in the basement
rocks. It is also known (in part) as the Tawe Valley Disturbance or the Swansea Valley Disturbance.
, formed both by glacial action during the ice ages and river erosion along this line of weakness in the Earth's crust between Abercraf
and Swansea. It is now occupied by the River Tawe
. The geologically complex mini-mountain of Cribarth
also lies on the Disturbance and indeed gives its name to the feature.
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
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 Fault, Southern Uplands Fault
, Highland Boundary Fault
and Great Glen Fault
are other major Caledonoid structures of Britain.
Lineament
See also Line 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 comprise a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these...
which stretches across south Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
from Swansea
Swansea
Swansea is a coastal city and county in Wales. Swansea is in the historic county boundaries of Glamorgan. Situated on the sandy South West Wales coast, the county area includes the Gower Peninsula and the Lliw uplands...
up the Swansea Valley
Swansea Valley
The Swansea Valley , one of the South Wales Valleys is the name often given to the valley of the River Tawe area in South Wales, UK. It reaches southwest and south from the Brecon Beacons National Park down to the city of Swansea. Today, administration of the area is divided between the City and...
then northeastwards to Brecon
Brecon
Brecon is a long-established market town and community in southern Powys, Mid Wales, with a population of 7,901. It was the county town of the historic county of Brecknockshire; although its role as such was eclipsed with the formation of Powys, it remains an important local centre...
and beyond. It comprises both a series of faults and associated fold
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
s which were active during the mountain-building period known as the Variscan orogeny
Variscan orogeny
The Variscan orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica and Gondwana to form the supercontinent of Pangaea.-Naming:...
. This line of weakness probably featured in the earlier Caledonian Orogeny
Caledonian orogeny
The Caledonian orogeny is 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 occurred from the Ordovician to Early Devonian, roughly...
and perhaps reflects a more ancient line of weakness in the basement
Basement Rock
Basement or Basement Rock music was a sub-genre coined in 2006 in an article by music magazine TGR. This was first in relation to the existence of underground record label Criminal Records but more for the independent bands they represent. The roots of the sub-genre are noted to be as far back as...
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 50km length. Prominent amongst these is the Swansea ValleySwansea Valley
The Swansea Valley , one of the South Wales Valleys is the name often given to the valley of the River Tawe area in South Wales, UK. It reaches southwest and south from the Brecon Beacons National Park down to the city of Swansea. Today, administration of the area is divided between the City and...
, formed both by glacial action during the ice ages and river erosion along this line of weakness in the Earth's crust between Abercraf
Abercraf
Abercraf is a village within the historic boundaries of Brecknockshire, Powys, mid Wales.- Location :Abercraf lies in the extreme south of the county, in the Upper Swansea Valley 2.5 miles northeast of the small town of Ystradgynlais...
and Swansea. It is now occupied by the River Tawe
River Tawe
The River Tawe is a river in South Wales. It flows in a principally south-westerly direction for some from its source below Moel Feity in the Old Red Sandstone hills of the western Brecon Beacons to the Bristol Channel at Swansea. Its main tributaries are the right bank Upper and Lower Clydach...
. The geologically complex mini-mountain of Cribarth
Cribarth
Cribarth is a hill in the Brecon Beacons National Park in the county of Powys, south Wales. The summit of the hill is at 423m and lies at the southwest end of a mile long ridge. It is marked by a trig point...
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 BritainGeological structure of Great Britain
The geological structure of Great Britain is complex, resulting as it does from a long and varied geological history spanning more than two billion years...
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
Iapetus Ocean
The Iapetus Ocean was an ocean that existed in the Neoproterozoic and Paleozoic eras of the geologic timescale . The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia...
in the middle Palaeozoic era and giving rise to the Caledonian Orogeny or mountain-building period. The Neath Disturbance
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 comprises a series of both faults and associated folds which were active during the mountain-building period known as the Variscan orogeny...
and the Carreg Cennen Disturbance
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 Borderlands Fault System...
are similar features also found in south Wales. The Bala Fault, Menai Strait Fault, Southern Uplands Fault
Southern Uplands Fault
The Southern Uplands Fault is a fault in Scotland that runs from Girvan to Dunbar on the East coast. It marks the southern boundary of the Scottish Midland Valley....
, Highland Boundary Fault
Highland Boundary Fault
The Highland Boundary Fault is a geological fault that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east...
and Great Glen Fault
Great Glen Fault
The Great Glen Fault is a long strike-slip fault that runs through its namesake the Great Glen in Scotland. However, the fault is actually much longer and over 400 million years old.-Location:...
are other major Caledonoid structures of Britain.