Pendine Coast
Geology & geomorphology
dx
LD
cl - Carboniferous Limestone
dx - Old Red Sandstone
LD major fault zone
Fig. 1 Geology
Fig. 2 Geomorphology
Figures 1 and 2 illustrate the geology and geomorphology of the ‘Three Rivers’ (Taf, Tywi & Gwendraeth)
area of Carmarthen Bay. It should be noted that the geological map shows the subsurface extent of the
rocks and they are generally not exposed at the surface.
Fig. 3 Ordnance Survey 1:50.000 map extract
Figure 3 shows the topography of the Pendine area in greater detail. The MOD range is situated on a
coastal plain backed by a dissected and bevelled remnant of a plateau surface. This higher ground falls
southwards and eastwards from 180m to 100m OD. There is an almost linear, steeply sloping boundary
between the dissected plateau and the coastal plain. From Pendine to Plashett (just NW of Coygen
Quarry) the A4066 follows the base of this slope, then continues along a glacial meltwater channel that
isolates St Johns Hill from the remainder of the plateau. Coygen Quarry lies on a fault bounded block of
Carboniferous Limestone but the remainder of the higher groud is on rocks of the Old Red Sandstone.
The southwestern extension of the Llandefaelog Disturbance (part of a regionally significant fault zone the Church Stretton Disturbance ) is shown on the geological map as a line passing along the base of the
slope of St Johns Hill and continuing WSW beneath the coastal plain to pass just offshore from Pendine
and Ragwen Point. The fault zone is probably more complex than this (as seen in the cliffs where it
reaches the coastline west of Amroth). A relatively minor earthquake (in terms of damage) occurred on
this fault in 1983. It had a magnitude of 5.0ML, and caused some minor structural damage to buildings
and visible disturbance of sea surface in nearby estuaries.
copyright Sid Howells
Figure 4 View east over Pendine Burrows
The MOD range is situated within an extensive dune system (Pendine - Laugharne Burrows) that
backs the 11km long sandy beach that extends from Dolwen Point to Ginst Point. This dune system
has partially encroached over an area of marshland/saltmarsh that has been reclaimed for agricultural
use. The dune system has also been modified to accomodate the MOD ranges and associated
infrastructure.
The area forms part of the Carmarthen Bay GCR (Geological Conservation Review) site, the
boundary of which is as shown in Figure 5.
Figure 5 GCR boundary (orange line) and MOD boundary (red triangles)
The Geological Conservation Review* was a very thorough, peer-reviewed evaluation of the total
geological resource of the United Kingdom, carried out by NCC
*see http://www.jncc.gov.uk/page-2947 for details.
* more detail is now available in published volumes, and the outline description of the Carmarthen Bay GCR site may be downloaded as a
.pdf file from
http://www.jncc.gov.uk/pdf/gcrdb/GCRsiteaccount2102.pdf
Details of all sites selected were passed on to district teams during the 1980's. It was specified that
all the geological interest described in the GCR citations* should have been notified as SSSI
features. Due to it’s size and complexity, this process has not yet been completed for the
Carmarthen Bay GCR site.
The GCR resource is considered to be the absolute minimum requirement for the needs of
geological science (research, education, etc) and public enjoyment in the UK. Thus all GCR sites
are of UK significance and many are of international significance to geological science.
Some unenlightened people might comment that geology is 'only about things that happened
millions of years ago' and therefore of lesser importance than biological conservation.
However, it should be remembered that geology students go on become specialists who find the
sources of many materials needed for our basic requirements (eg. building stone, oil & gas, coal,
metalliferous minerals etc) or whose advice is critical to the success of civil engineering and
environmental management. Gaining a better understanding of coastal processes will be critical to
decision making in relation to sea level rise and increased storminess associated with climate
change.
The GCR sites within Carmarthen Bay are also fundamental to biodiversity whilst the scenery is
greatly appreciated by a wide range of people and is crucial to tourism.
The Carmarthen Bay GCR site is very large and complex. It covers both the natural landforms and
the active processes (eg. wave action, sand movement, etc)
The following paragraph (from May & Hansom, 2003) provide a very basic description of the
geomorphology of the coastline between Pendine and Laugharne.
Pendine Sands and Laugharne Burrows are dominated by dunes up to 700 m wide that extend
some 9.5 km to Ginst Point (SN 331 078). The dunes attain heights in excess of 15 m, except
in the vicinity of Wickett Pill where a stream draining marshland and a shallow lake existed up
to the 1950s. Since then, there has been considerable accretion of Laugharne Burrows, but the
shoreline of Pendine has remained virtually static. The intertidal zone is up to 1 km in width,
notably opposite Wickett Pill. As the dunes grew eastwards they protected the rocky cliffs *
(Savigear, 1952) and the intervening marshland was reclaimed. North of Ginst Point, saltmarsh
has developed in the lee of the dunes and in front of artificial embankments. The eastern part
of the reclaimed marshland drains via Railsgate Pill into the Taf estuary at SN 306 099.
* the writer does not concur with this hypothesis
It has to be said, from a purely geomorphological/landscape/amenity viewpoint, that the changes
to the dune system and marshland behind Pendine Sands, and the coastal engineering works at
Ginst Point, have been highly undesirable modification of a very special natural landscape. Such
modification would not be permitted today.
However, in view of likely rise in sea level and re-adjustments of the dune system that might occur
such issues are likely to become irrelevant.
Sid Howells, 03/2010
Figure 6 Ginst Point
copyright Sid Howells