| Site Description |
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| Highlights: |
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| The White Rocks, extending to the east from the Curran (East) Strand to Dunluce on the Portrush-Portballintrae coast, Co. Antrim, are a stretch of Cretaceous Chalk cliffs which demonstrate classic coastal landforms in chalk - cliff, shore platform, cave, arch, and sea stack. |
| Introduction: |
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| The chalk which constitutes the cliffed coast between the White Rocks and Dunluce forms some of the hardest rocks in Northern Ireland and produces a set of distinctive coastal landforms. |
| No detailed geomorphological work has been done on these features. The site is described briefly by Carter and Bartlett (1988), and Carter (1991). There have been sparse references to landform development in the geological literature, e.g. Wilson and Manning (1978) view the cliffs, caves and chalk platform as post-glacial age in part, although substantially modified by recent marine erosion. |
| Description: |
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| For 2km east of the Curran (East) Strand at Portrush, Co. Antrim the shore is formed of near vertical chalk cliffs fronted by an impersistent platform. There are occasional inlets and small embayments, mostly structurally controlled. The cliffs trend WSW- ENE and extend to Dunluce Castle where a fault re-introduces the basalt shoreline with wider shore platforms, and cobble/boulder beaches. |
| The shoreline comprises a rampart of chalk cliffs and associated features, including caves at various stages of development, blowholes, shore platforms and cliff benches, stacks, and sea arches. The cliff-base platform is a discontinuous, narrow, low-elevation feature, riven by NE-SW trending joints matching the orientations of numerous rectilinear caves in the chalk promontories. Sub-horizontal Lower basalts cap the chalk along much of this coastal section. On the west the cliff is often cut entirely in chalk, but to the east the basalt forms the upper cliff face. |
| The chalk landforms are best developed in two locations at either end of the site. At the western (Curran Strand) end, flanking the Slidderycove Point promontory, there are a number of deep rectilinear caves and an impressive arch. Here also a number of sea stacks stick up from the sand. Some of these are composed of chalk which has been shattered and recemented. Large blocks of basalt are sometimes embedded in this material. At the eastern (Dunluce) end of the site there is the spectacular Gulls Point arch with basalt caprock on the cliffs to landward. Associated with this arch are a number of caves, smaller incipient arches, and sea stacks. |
| The great depression of The Riggin appears to be a collapse structure - a former chalk cavern or system of caves that has suffered roof collapse. Waves now enter The Riggin through several openings in the narrow chalk ridge which separates it from the sea. |
| The chalk cliffs are steep, with vertical or slightly convex profiles. A characteristic feature of the cliffs which sets them apart from the basalts are the large smooth-walled depressions which in several places occupy a large part of the cliff face above the basal bench. The site demonstrates textbook examples of slope-over-wall cliffs, where the upper vegetated slopes give way to near vertical faces at the shoreline. The cliff-base shore platform is best developed between Sliddery Cove and Jackstone Cove. |
| There is virtually no storm beach development in the re-entrants. At most there is a low ridge of flints and basalt clasts, the latter originating as rockfall from the lavas capping the chalk. |
| Importance: |
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| Chalk is one of the two dominant lithologies over much of the north-eastern quadrant of Northern Ireland, the other being basalt. Yet virtually nothing is known of the details of its response to marine processes. The White Rocks, sandwiched between the sand beach of the Curran Strand and the basalt cliffs east of Dunluce, illustrate the landforms typical of chalk coasts. The juxtaposition within a short alongshore stretch of three quite different coastal environments allows comparison of their features. |
| The cliffs can be accessed for a short distance on their eastern side from the Curran Strand. A short distance further east the narrow platform at the cliff base peters out, and further progress from the landward side is virtually impossible. The features lying further east, e.g. the Gulls Point arch, can only really be viewed from the cliff top. The site is already popular as both an educational and recreational resource, and its aesthetic quality is very high. |
| Interpretation: |
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| The Irish Chalk (White Limestone) is highly resistant to erosion, and forms a stark contrast with the friable chalk of the coast of southern Britain. The chalk cliffs between the White Rocks and Dunluce demonstrate this characteristic as very little evidence of recent coast erosion is apparent - at least on a macro scale. Comparison of photographs taken over the period 1890 to 1987 shows almost no changes in the cliff faces, even on the most exposed sites. Just east of Jackstone Cove a fresh erosional bench formed by recent wave quarrying is the only substantial evidence of recent, relatively large-scale marine erosion. |
| However, while the gross morphology appears to change very little, more detailed examination of the lower sections of the cliffs and platforms reveals many fresh erosion scars. These are easily distinguished from the surrounding weathered or abraded surfaces by their fresh white appearance. The White Rocks landforms were created as a result of differential erosion by storm waves which have preferentially attacked the lines of relative weakness provided by NE-SW trending joints and fractures, and smaller scale discontinuities including cracks and small faults. All stages of the process can be seen, ranging from small wave gullies and incipient caves developing along well defined shore-oblique joints, to large caves, arches and sea stacks formed by progressive enlargement of the smaller caves by marine and subaerial processes. |
| Despite the erosional appearance of the chalk cliffs, it is not possible to detect any recent block falls or slope failures. It may be that subaerial weathering and slope processes on chalk operate in a slower, more subtle, chemical mode, but no work has been done on this aspect of the chalk. The smooth-walled depressions which give a characteristic convexicity to the cliff faces may result from high level storm wave attack on the chalk, and hence be best regarded just as well-developed wave notches; but investigation may reveal whether sub-aerial weathering processes play any part in creating this morphology. |
| Wilson and Manning (1978) assume that these chalk landforms are raised features dating from a Holocene higher RSL, although they concede that modification has taken place in contemporary times. Certainly it is possible, perhaps probable, that the cliffs and associated features were initially eroded at an earlier and slightly higher RSL, perhaps the maximum Post-glacial RSL estimated by Carter (1982) to have attained approximately 2-4m above present, c. 5500 to 6500 yr BP. |
| However, there is no compelling reason to invoke a higher RSL to account for the present morphology. Even in moderate storms the cliffs, caves, arches and stacks are well inside the zone of contemporary storm wave influence. The coastal stretch east of the White Rocks is no longer in the Skerries wave shadow, so is open to the full power of refracted Atlantic swell and locally generated storm waves. The relatively deep water close inshore also enables large waves to reach close to the cliffline. |
| Conclusions: |
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| The chalk cliffs at the White Rocks comprise arguably the best and most accessible stretch of classic chalk landforms in Northern Ireland. Their aesthetic value is also high. |
| Notes: |
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| Little research has been carried out on the coastal expression of the Irish chalk which, although chemically identical to the English sites, is harder and less friable as a result of contact metamorphism with the overlying basalts. Preliminary appraisals suggest the two lithologies to differ in terms of cliff profile and shore platform development. |