The Carmarthen Raceway

I notice that there is a valley in south Wales that has had a very important role in shaping the coastal topography of the southwestern part of the country. I did a survey of the landscape of Wales using http://www.maps.google.com/ as well as the more advanced Google Earth, which is not free on the internet. This valley extends from the town of Carmarthen northeastward to Builth Wells. In surveying the valley using Google Earth, I started in Builth Wells and found my way to Carmarthen by following the area on the screen lowest in elevation above sea level.

The great effect that this valley must have had on the Welsh coast centers around what happens at the end of each of the successive ice ages. As the climate gets warmer, the glacial ice in the warmer lowlands will melt first. As the ice in the mountains begins to melt and break apart into large bergs, it slides along valleys such as this, which I have termed "The Carmarthen Raceway", on the way to the sea. As it does, it reshapes the coastline.

Ice usually covers about 10% of the earth's surface but during ice ages, that increases to maybe 30%. There is known to have been more than twenty such ice ages.

(Note to readers- In this posting I have attempted, as far as is possible, to select landmarks that have English, rather than Welsh, names. Cities tend to have English names but many towns and villages in Wales have Welsh names. This is not intended as an affront to Wales, which is a fabulous and scenic place, but only for the ease of my readers. Welsh names are not pronounced as they appear in English and three Welsh letters are not used in the English language and are written in Welsh as doubles- FF, LL and, DD.)

Carmarthen Bay on the south coast of Wales was dug by ice moving through the Carmarthen Raceway at the end of each ice age. Using the satellite imagery on http://www.maps.google.com/ you can easily see how cliffs alternate with beach around the coast of Carmarthen Bay, the shadows of the cliffs can be seen. This is because, ice from the Raceway will carve away the cliffs to form a low area and then moving ice from successive ice ages will follow the same low path. This leaves cliffs intact in some places but erases the cliffs to form beach in others.

Notice how there is much more sand, including the vast Pendine Sands, on the eastern side of Carmarthen Bay. This is simply because of the northeastward direction of the waves from the ocean.

There is much more cliff that has survived the ice ages around Saundersfoot on the western shore of the bay because that was more in line with the direction from which ice came from the Carmarthen Raceway. At the holiday town of Tenby, at the southwestern corner of Carmarthen Bay, there is an extensive stretch of beach facing east but a short distance away, there is no beach facing south. This plainly illustrates how the moving ice removes cliffs to form beaches and the direction of the Carmarthen Raceway from which it came.

Notice the two small islands just off Tenby that are islands at high tide but not at low tide. It is obvious that these satellite images were taken at low tide because many small boats can be seen on the sand at Saundersfoot and Tenby.

From high up, you can see that there are two long stretches of wide beach that are parallel to each other, along the same axis. One is at Tenby and the other is from Saundersfoot to Amroth. These point along the main direction of the moving ice and point directly at the Carmarthen Raceway.

Caldey Island, the large island south of Tenby, was cut away from the mainland by the ice over successive ice ages. From above, it is easy to see how the island is gradually being cut up by the ice. The buildings on the island are a Cistercian monastery. (I believe it is also spelled "Caldy" but on the map it is mispelled "Caldney")

I notice many of what I will call "gorges" on the southwestern coast of Wales. I call them this because they remind me of miniature versions of the one at Niagara Falls. There are three of them in a row on the coast south of Buckspool, west of Tenby. I am certain that these gorges are the first step in the destruction of a stretch of cliff to form a beach. Gorges are narrow while beaches are wide. They are most likely formed by flowing meltwater from glaciers that forms a waterfall over the cliff and erodes it's way backward.

Moving westward, the city of Milford Haven lies in a low area near the coast with a river. This is actually the deepest waterway in Europe and was obviously carved out by moving ice. Remember that bodies of water dug by glaciers tend to be either broad and shallow or narrow and deep.

The form of the coast around the inlet to Milford Haven is similar to that of southwest Ireland and was formed in the same way. It is easy to see the path of the ice here at Sandy Haven, west of Milford Haven, and by the extensive beach at Castlemartin nearby.

In my estimation, there are three main tracks that the ice from the Carmarthen Raceway follows on it's way to the sea at the end of each ice age. The first is that which formed Carmarthen Bay. The second is that which dug the waterway at Milford Haven. The third is the one which created St. Bride's Bay to the north of Milford Haven.

At the southwestern corner of St. Bride's Bay there is very rugged rock that has resisted the ice while being "polished" by it. You can see how Skomer and Skokholm Islands were cut away from the mainland by the ice, just as Caldey Island was. Notice how the southward shore of Skomer Island is much more rugged than it's northern shore because this is the direction in which the ice was moving.

The thing that is so interesting about St. Bride's Bay is that wide beaches are to be found only on it's eastern shore because this is the direction from which the ice came. The eastern shore, in sharp contrast to the other shores, is more beach than cliff. There are relatively few cliffs there, such as the one at Broadhaven.

Another point of interest concerning St. Bride's Bay is that there are many narrow gorges on it's northern shore but none on it's southern shore. The ones on the northern shore all point to the southwest, the direction in which the ice was moving from the Carmarthen Raceway.

Waves from the ocean are certainly also a factor in the erosion and shaping of coastlines such as this, but by far the main factor was this ice. There are many videos on http://www.youtube.com/ of this area of the Pembrokeshire coast so you can see up close what it looks like.

In my survey of the Welsh coast, I notice that the west coast of Wales gets smoother as we go north. This is because it was away from the ice flow of the Carmarthen Raceway. The coast gets noticably smoother north of New Quay and smoother still north of Aberystwyth (This is the Welsh name of Wales' most important west coast city but English people say it the way it looks in English, although this pronounciation is not technically correct.) However, north of Caernarvon Bay to Holyhead the coast becomes rugged again. Anglesey clearly displays the southwest to northeast lines of primary glacial movement from beyond the shield provided by the mountains of Wales.

Going back to south Wales, you will notice another bay to the west of Carmarthen Bay by the name of Swansea Bay near the city of that name. This bay was formed in exactly the same way as Carmarthen and St. Brides Bays. There is a valley northward from this bay up to Brecon Beacons through which flows the Neath River. This valley operated as a raceway for the ice in the same way as the Carmarthen Raceway.

Far to the north on the west coast of England is the large Morecambe Bay. This was also formed by bergs of ice at the end of ice ages flowing through a nearby valley after coming down from mountains. In surveying Morecambe Bay by the satellite imagery, it does not seem to have the cliffs around it that the Welsh bays do and this made the erosion faster and more extensive to form a larger bay.

On the far western tip of France we find the same type of phenomenon. I did a survey of this area and there is the same alternation of cliffs and beaches. Notice that Baie de Douamenez and the nearby waterway at the city of Brest is very similar to St. Brides Bay and the nearby waterway at Milford Haven. The main difference is that in Wales, the bay is to the north of the glacial waterway while in France it is to the south.