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White Rocks - Coastal GeomorphologyAntrim
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Summary Full report
Site Type: Cliff, Coastal section
Site Status: PASSI
District: Coleraine Borough Council
Grid Reference: C891409, C906416
Rocks
Rock Age: Quaternary, Cretaceous (Holocene, Santonian)
Rock Name: Ulster White Limestone Formation
Rock Type: Limestone
Interest
Other interest: No data, Coastal processes, arch, cave, cliff, shore platform, stack

Summary of site:

This account describes the geomorphology of the White Rocks. Their geology is treated separately (sites 1188 and 1207).

This is the most exposed coastline of Ulster White Limestone around the shores of Northern Ireland and, though protected somewhat by the Skerries from the massive north Atlantic storm waves that can develop over a reach of 3,000 km, it is still heavily pounded in foul weather. The Ulster White Limestone is of similar age to the Chalk coastal cliffs and Downs of the south and east coasts of England and although it was formed in an almost identical environment (as a creamy ooze on a warm, relatively shallow sea bed) its subsequent history has cemented it into a hard, resistant rock quite unlike its English equivalents. In consequence its interaction with the sea produces very different landforms and a coastline of uncommon character. Another major contributing factor is the pattern of jointing pervading these rocks. Joints are natural fractures (resulting from stored stress) usually in two sets at right angles, passing through the rock but, unlike faults, there has been little perceptible movement along them. The cliffs are generally convex in profile and show the classic landforms of rocky coasts including sea caves, some with blow holes, natural arches (where the sea has penetrated a headland, normally along a joint), stacks (isolated pillars left when an arch collapses), shore platforms (truncated rock forming a terrace along the foreshore under a cliff) and benches (horizontal cliff hollows). The best examples are at the extremes of the outcrop, in the west where the Curran Strand ends and in the east, about half a kilometre west of Dunluce Castle, where the cliffs are capped by the Lower Basalt Formation. Sliddery Cove at the west end has a number of linear caves exploiting the joint planes, abruptly changing direction to follow cross joints: there is also a fine arch and several sea stacks projecting directly from the beach sand. At the other end is the superb Gulls Point arch with more caves, stacks and openings through cliff ramps not quite fully developed into arches. The Riggin is a well-known depression separated from the sea by a small ridge. It appears to be due to a sea cave system that became so extensive that it could no longer support its roof, resulting in a cave-in still washed by the sea. Just when the major cliff features were formed is open to speculation. There is no storm beach of accumulated rock here, no isolated fallen blocks, an absence of slope failure, virtually no change between the cliffs on 19th century photographs and their present appearance. The only discernible changes are in the lower cliffs within reach of modern storm waves where there is minor sapping in the form of wave notches. This has led some authorities to suggest that the main cliff architecture formed when sea level was higher, probably between 5 and 6 thousand years ago, when it was at its maximum. Others point out that the cliffs are almost fully exposed to modern storms and deep water just off the shore permits large waves to reach them. This regime could create all the features seen at White Rocks. While this is so, the unweathered upper cliff, clearly differentiated by its darker organic cover, suggests centuries, if no millennia of stability. These commanding cliffs with their wealth of features form the best Ulster White limestone coastal morphology in Northern Ireland and should be designated in recognition of this interest.


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