Previous SiteNext Site

Larrybane Stalactite Cave, Larrybane BayAntrim
General view of Larrybane Stalactite Cave, Larrybane Bay, Co.Antrim, showing cave mouth, tufa columns and associated overhang in 1997.
Summary Full report
Site Type: Cave, Cliff, Coastal section
Site Status: NT
District:
Grid Reference: D055448
Rocks
Rock Age: Quaternary, Cretaceous (Santonian)
Rock Name: Ulster White Limestone Formation
Rock Type: Limestone, Tufa
Interest
Other interest: No data, Coastal processes, Ice-plucking, photokarst, raised beach, sea cave, tufa

Summary of site:

This site is both unusual and unique in its karst interest.

Larrybane Bay is backed by a curtain of 30 m high Ulster White Limestone cliffs with fine active sea caves at its western end. In the middle of the bay there is a prominent and very unusual cave, its entrance guarded by three massive and spectacular tufa pillars and three stumpy stalactites. It is 7 m above high tide mark and is approached over a jumble of grassed boulders banked against the base of the cliff, the products of earlier rock falls and now beyond the reach of the sea. Its floor aligns with a strongly developed terrace, the so-called ˘25 foot raised beach÷ of earlier descriptions, that notches the cliff producing impressive overhangs in places, some over 5 m deep. The cave entrance is sheltered below such an overhang. Beyond the tufa pillars and stalactites the cave is only a few metres deep and, unusually for a coastal cave, very angular in its internal geometry with sharply defined walls and roof. The tufa is restricted to the cave entrance. There are many stalactites on the roof of the overhang and they can be seen to relate to a seepage of water draining down the cliff, depositing tufa on all the surfaces it washes over. A wider inspection of the cliffs shows this to be one of many seepages, all laying down tufa, though not as spectacularly as at the Stalactite Cave. Minor features of the cave are small stalactites that appear to defy gravity and grow outwards towards the entrance, a gours pool with creamy white cave pearls (some slightly blue-tinged) and vertical tufa ridges on the east wall. The cave, like many others situated immediately above the ˘25 foot raised beach÷, is a sea cave formed when sea level was approximately 7 m higher than it is today. This suggests that it formed immediately after the Scottish ice had detached from the north coast but not too long afterwards because the land was still experiencing the depressive effects of the massive thickness of recently melted ice. The angular interior of the cave shows that it was not a typical sea cave (normally more smooth and rounded) and suggests that the plucking effect of seasonal sea ice locked onto the cliffs or rock failure due to frost action exploiting joints and bedding planes loosening blocks that were then more easily extracted, played some role. Exactly in what period tufa development in the cave commenced is difficult to say but it must have been sometime after a significant fall in sea level had left the caves beyond the reach of storm waves. Early growth stages of stalactites and stalagmites are fragile and would not have survived severe pounding. Tufa is formed when water saturated with dissolved calcium carbonate by its passage through the rock, here the Ulster White Limestone, emerges into open air. In a cliff seepage it forms a film over the rocks of the cliff face and gathers at the edges of overhangs where the dissolved carbon dioxide is lost, water evaporates and calcium carbonate is precipitated. This process is accelerated by higher temperatures again suggesting that it began after the departure of the ice sheets. There is also much evidence that the development of cave formations was and still is, influenced by plant growth, particularly of bryophytes and alg'. Bryophytes considerably increase the surface area for evaporation encouraging rapid growth of formations. The slanting stalactites appear to result from plant growth on surfaces facing the light which are then selectively enhanced by the same process. Depending on their situation, plants can also cause minor erosion, creating small scale ridges and pits also facing the light. These are a consequence of acid released as plants decay, etching the pure limestone into fragile karst features often described as photo karren which are also a feature of Larrybane Stalactite Cave. There are at least three other well developed raised sea caves in the bay sharing a range of features seen in the Stalactite Cave but none has the bold cave formations that create its distinctiveness. This raised sea cave is unique in Northern Ireland combining a range of phenomena including association with the ˘25 foot raised beach÷, the exceptional development of tufa deposits unparalleled elsewhere on the Ulster White Limestone outcrop, substantial columns, stalactites and stalagmites, and an unusual angular form probably dating back to the time when pack ice seasonally locked onto the cliffs. This rare combination of interest is worthy of Area of Special Scientific Interest status. The site is in the ownership of the National Trust and there appear to be no threats except from the elements.


Previous SiteNext Site

|Home|