Coastline of Wales
The coastline of Wales extends from the English border at Chepstow westwards to Pembrokeshire then north to Anglesey and back eastwards to the English border once again near Flint. Its character is determined by multiple factors, including the local geology and geological processes active during and subsequent to the last ice age, its relative exposure to or shelter from waves, tidal variation and the history of human settlement and development which varies considerably from one place to another. The majority of the coast east of Cardiff in the south, and of Llandudno in the north, is flat whilst that to the west is more typically backed by cliffs. The cliffs are a mix of sandstones, shales and limestones, the erosion of which provides material for beach deposits. Of the twenty-two principal areas which deliver local government in Wales, sixteen have a coastline, though that of Powys consists only of a short section of tidal river some distance from the open sea. Its length has been estimated at.
Geological history
Parts of the Welsh coast are formed by bedrock of Precambrian age, notably along the north coast of Llŷn and Pembrokeshire and parts of Anglesey. These oldest rocks are generally igneous or metamorphic in nature and typically hard-wearing. Much of the cliffed coast of Cardigan Bay is in turbidites and allied rocks of Ordovician and Silurian age. Devonian age Old Red Sandstone provides the coastal scenery around much of Milford Haven whilst low cliffs of Carboniferous Limestone forms the coast in parts of Anglesey. At some other localities along the north coast such as the Ormes at Llandudno, cliffs in the same rock are considerably higher. The same limestone characterises much of the southern coast of Pembrokeshire where the flat-lying strata produces sheer cliffs though in Gower, the same limestone strata were more intensely faulted and folded during the Variscan orogeny, and the cliffs are accordingly more variable. Limited outcrops of Triassic sandstones and mudstones occur on the south coast. They are typically overlain by flat-lying Jurassic limestone which forms much of the coast of the Vale of Glamorgan; these well-jointed vertical cliffs are more prone to collapse and hence coastal retreat is relatively rapid.In common with other parts of Britain and Ireland, Wales has experienced significant changes in sea level in the last few tens of thousands of years, largely attributable to the waxing and waning of ice sheets during successive glacial periods, the last of which ended only 11,500 years ago. At the height of the last ice age, the volumes of water locked away as ice resulted in a drop in global sea level which has been estimated at between and a corresponding change in the position of the coast. During this period of lowered sea level, the lower sections of many rivers were rejuvenated and they cut down into their beds as evidenced by the buried channels of the Usk at Newport and the Wye at Chepstow which are more than below sea level respectively. The Flandrian transgression associated with the melting of the ice-sheets has brought the sea level to that recorded over human history, with the larger part of that rise achieved prior to 6000 years ago. Within Cardigan Bay, three 'sarnau' or causeways - Sarn Badrig, Sarn Gynfelyn and Sarn y Bwch - extend out from the coast for several miles, parts being exposed at low spring tide. These are interpreted as medial moraines left by ice moving west off the Cambrian Mountains during the last ice age. The position and character of the modern coastline owes much to the manner in which sea level has adjusted since.
Peat deposits and tree stumps are exposed in the intertidal zone in many places along the Welsh coast. They date from a time of lower sea level around 8000 years ago. The traditional Welsh legend of the drowned land of Cantre'r Gwaelod has been linked to these localities. A stormier climate between about 1300 and 1700 led to large quantities of sand being blown onshore and increasing the size of the various dune systems.
Tidal range
Cardigan Bay experiences the lowest tidal range along the Welsh coast whilst the Bristol Channel coast experiences the highest. Indeed, the tidal range within the funnel-shaped estuary is the third or fourth highest in the world. A result is that the intertidal zone is larger than might otherwise be the case.Shore platforms
'Shore platforms' are developed along rocky coasts and are commonly referred to as 'wave-cut platforms' though that name ignores the contribution that other processes may contribute to their development. They are well-developed along parts of the Welsh coast - for example, south of Aberystwyth and along the Glamorgan Heritage Coast.Physical features
The Welsh coast is diverse with both sandy and rocky bays frequently interspersed with estuaries and headlands.Estuaries
There are a large number of estuaries around the Welsh coast. Two of the largest are shared with England; that of the Dee in the northeast and of the Severn in the southeast. The Milford Haven Waterway which penetrates deep into Pembrokeshire is notable as an outstanding example of a ria, a river valley which has been drowned by a rise in sea level. The estuaries of the Towy, Loughor and Usk also owe their origin to rising sea levels in the post-glacial period. The Severn, Dee and Clwyd estuaries experience tidal bores under certain conditions. Estuaries typically provide ecologically rich habitats but they have also been attractive for human settlement and port development.Peninsulas and headlands
The county of Pembrokeshire forms the largest peninsula in Wales and contains within it, several smaller peninsulas such as the Dale peninsula and St David's peninsula; the headland of Pen Dal-aderyn at its extremity is the westernmost point of the Welsh mainland. Second in size is the Llŷn Peninsula in the northwest and third is the Gower Peninsula in the south. Like most of Gower, the Great Orme at Llandudno which is the most notable headland on the north coast, is formed from relatively erosion-resistant Carboniferous Limestone. Other notable headlands include Lavernock Point, south of Cardiff, and Worm's Head which is the westernmost point of Gower. The northeasternmost point of Wales is provided by Point of Ayr.Bays
is much the largest bay on the Welsh coast but dozens of others are found at a variety of scales.Dune systems
Major dune systems occur at intervals around most of the Welsh coast. The majority are "bay dunes" as commonly found around the Pembrokeshire coast. Some, known as "hindshore dune systems", occur where the prevailing wind has driven sand inland as at Newborough Warren in southwest Anglesey whilst others such as that at Whiteford Burrows in northwest Gower have developed along sandy promontories and are referred to as "spit dune systems". The system at Morfa Harlech has also grown behind a spit; this one is developed across the mouth of the Dwyryd estuary. Several form the core of national nature reserves such as those at Kenfig Burrows and Merthyr-mawr Warren to the north and east of Porthcawl respectively.Salt marshes
es are found in many areas. Amongst the most significant are those on the southern side of the Loughor estuary on Gower's north coast. Significant areas of salt marsh are also found within the Dee estuary and between Harlech and Porthmadog though, here as elsewhere, reclamation of large parts of the marsh have taken place in the past for use as farmland.Islands
is easily the largest Welsh island, separated from the mainland in the northwest of the country by the Menai Strait.Smaller islands off Anglesey include Wales' second largest, Holy Island and Puffin Island or Priestholm. Anglesey is connected to the mainland by two bridges and Holy Island is connected by both a bridge and a double causeway. Llanddwyn Island is only separated from mainland Anglesey at high spring tides.
Off the coast of Llŷn are Bardsey Island, St Tudwal's Island East and St Tudwal's Island West. Off the Ceredigion coast are Cardigan Island and the diminutive Ynys Lochtyn. Wales' third, fourth, fifth and sixth largest islands are scattered around the Pembrokeshire coast; respectively Skomer, Ramsey Island, Caldey Island and Skokholm. Others in this area include Midland Isle and the tidal islands of Gateholm, Ynys Micel, Sheep Island and St Catherine's Island. St Margaret's Island is linked to Caldey at low tide. Off Gower are the tidal islands of Worms Head, Middle Head and Mumbles Head. In the southeast, Sully Island is linked to the Glamorgan coast at low tide whilst Flat Holm is 3 miles off the coast at the east end of the Bristol Channel and is the southernmost part of Wales. Wales' most isolated island, and its westernmost island, is Grassholm, west of Skomer though the wave-washed rocks supporting the Smalls Lighthouse at more than twice that distance from Skomer are the westernmost part of Wales.