The Neath Disturbance is a geological structure which stretches across south

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

from

Swansea Bay Swansea Bay ( cy, Bae Abertawe) is a bay on the southern coast of Wales. The River Neath, River Tawe, River Afan, River Kenfig and Clyne River flow into the bay. Swansea Bay and the upper reaches of the Bristol Channel experience a large tid ...

northeastwards as far as

Hereford Hereford () is a cathedral city, civil parish and the county town of Herefordshire, England. It lies on the River Wye, approximately east of the border with Wales, south-west of Worcester, England, Worcester and north-west of Gloucester. ...

in western

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

. It consists of a series of both faults and associated folds 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 f ...

. 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 ...

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. The Disturbance gives rise to 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-alig ...

crossing the region, that is to say that it is responsible for a number of significant landscape features along its 100 km length. Prominent amongst these is the Vale of Neath, a deep valley incised by a

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

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 ...

along this line of weakness in the Earth's crust and now occupied by the

River Neath River Neath ( cy, Afon Nedd) is a river in south Wales running south west from the point at which its headwaters arising in the Brecon Beacons National Park converge to its mouth at Baglan Bay below Briton Ferry on the east side of Swansea Bay. ...

between

Pontneddfechan Pontneddfechan, also known as Pontneathvaughan (pronounced ) ("bridge over the Little Neath" in Welsh) is the southernmost village in the county of Brecknockshire, Wales, within the Vale of Neath, in the community of Ystradfellte and in the pri ...

and

. The hill of Moel Penderyn also lies on the Disturbance a little further east. A part of the Vale of Grwyne north of The Sugarloaf and the northeast-southwest aligned section of the Monnow valley on the English/Welsh border are also excavated along this line of weakness.British Geological Survey 1:50,000 map sheets 214, 215, 231 'Merthyr Tydfil', 232 'Abergavenny', 247 'Swansea' & accompanying memoirs The Neath Disturbance is possibly the southernmost geological feature within Britain which can be described as following the Caledonoid trend. The phrase describes a suite of major 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 paleo ...

in the middle

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

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

Cribarth Cribarth, sometimes referred to as the Sleeping Giant, is a hill in the Brecon Beacons National Park located in the traditional county of Brecknockshire (currently administered part of the unitary authority of Powys) in southern Wales. The summit ...

Swansea Valley The Swansea Valley ( cy, Cwm Tawe) 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 Sw ...

Disturbance 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 Dist ...

are similar features found a little further north in south Wales. The

Bala Fault The Bala Fault is a SW-NE trending geological fault in Wales that extends offshore into Cardigan Bay. In the offshore area it is a major normal fault and forms the bounding structure to the Cardigan Bay Basin, with a fill including about of Lias ...

Menai Strait Fault Menai may refer to the following places: Australia * Menai, New South Wales Africa * Menai Bay on the island of Zanzibar, Tanzania * Menai Island, a Cosmoledo atoll islet, Seychelles Europe *Menai, an electoral ward in Bangor, Wales, UK *Menai (Ca ...

, Southern Uplands Fault, Highland Boundary Fault and

Great Glen Fault The Great Glen Fault is a strike-slip fault that runs through the Great Glen in Scotland. The fault is mostly inactive today, but occasional moderate tremors have been recorded over the past 150 years. Location Aligned northeast to southwest, t ...

are other major Caledonoid structures of Britain.

References

{{reflist Geology of Wales