Rine Point, un cordon de galets et de sable de la baie de Galway (Comté de Clare, Irlande) et formes associées

Abstract

ABSTRACT Rine Point is a 2,2 km gravel spit on the south coast of Galway Bay in Co. Clare, western Ireland. The spit is composed of Carboniferous Limestone either derived directly from marine erosion of the Burren Limestone cliffs around Black Head and] or from the shore platforms, or, indirectly, from local glacial deposits (mainly periglacial head). Clasts from these sources have moved east into Galway Bay under a unidirectional regime of decaying Atlantic swell. Initially, the material forms a 2 km fringing ridge made up of gravels, cobbles to boulders, but this passes alongshore into the Rine Point spit. The spit is divided into a series of small (up to 250 m) discrete cells or embayments. These are formed either as the spit tries to attain a local quasi-equilibrium with the incident swell (see Carter et al., 1987) or are associated with irregularities in the frontal rock platform. In several places the spit has been breached and the distal extremity has been beheaded, leaving two residual islands. A distinct cross-shore zonation is apparent. The rock platform and pebbles show excellent examples of bioerosion features. The beachface is formed of rounded gravels, with shell sand patches in the updrift parts of the cells. The ridge crest and back barrier slope are capped with a thin, stratified shelly sand, containing occasional molluscs. In places, small, high level storm breaches have occurred creating fan-shaped gravel washovers. The spit encloses a small tidal marsh, which drains east into a tidal flat. The present day sediment input to Rine Point is probably negligible. To the west, sediment suppy to the coast has been impeded by the building of the coast road and the longshore drift reduced after the building of a small harbour near Black Head in the late-nineteenth century. Much of the remaining cliffline is now naturally armoured with boulder deposits. The morphology of Rine Point suggests strongly that it is a mature feature, which may be entering a phase of decay and break-up.