DISTRIBUTION OF COASTAL BOULDER DEPOSITS ON THE ARAN ISLANDS, IRELAND

Coastal boulder deposits (CBD) are found on coasts and cliff tops all over the world, but those on the Aran Islands (off the west coast of Ireland) are among the best documented. Their combination of lithologic consistency and consistent wave climate (with strong prevailing wave approach direction), coupled with geomorphic variability, makes them an ideal candidate for detailed analysis of the relationship between local inshore wave height and CBD development.

These islands consist of three main land masses: Inishmore, Inishmaan, and Inisheer. Over centuries and millennia, waves from strong winter storms have created prominent CBD along cliffs and shore platforms on the Atlantic Coast of all three islands. However, locations with similar elevations and wave climates may or may not show CBD. This study uses both existing CBD field measurements and new measurements extracted from satellite imagery and high-altitude orthophotographs, in conjunction with modeled hindcasts for near-shore sea states, to quantify relationships between CBD location, topographic setting, and wave climate. Initial results reveal a probabilistic relationship between inshore wave conditions and CBD occurrence, based on dimensionless analysis of wave heights and coastal elevations.

Further analysis will provide probabilities of occurrence as well as offer explanations for why locations with similar elevations and wave climates may show either the presence or absence of deposits. Dimensionless parameters introduced here, including a cliff elevation to wave height ratio, will allow this new approach to be translated to other sites. Determining these relationships will contribute to the ongoing need to better understand the interactions between extreme storm waves and rocky coasts.