Cliff-top megaclast deposits of Ireland, a record of extreme waves in the North Atlantic—storms or tsunamis?

Patterns and rates of erosion produced by high energy wave processes on hard rock headlands: The Grind of the Navir, Shetland, Scotland

“…Sunamura (1992) has collated global data on cliff recession and estimated average rates of retreat on granite cliffs at 0.001 mm/yr, several orders of magnitude less than in the ignimbrites at The Grind, confirming that rates of hard rock cliff erosion here are very high. However, similar rates of 0.4 mm/yr have been estimated for cliffs with CTSDs on Aran (Williams and Hall, 2004). It is likely that long-term rates of cliff retreat are higher than estimated as no major failure of the cliff face has occurred over the past century.…”

“…marina quickly colonises relatively sheltered surfaces on cliffs (Williams and Hall, 2004). Thalli diameters reached an average of 30 mm in 10 years on block surfaces exposed by the 1992-1993 storms on the highest points and rear of the cliff but this lichen is absent from rock surfaces of this age at The Gateway, presumably due to the greater exposure at this site.…”

“…The rear of the platform holds a striking series of boulder ridges up to 3.5 m high where blocks continue to accumulate. Whilst this assemblage of features is replicated at other CTSD sites (Williams and Hall, 2004;Hall et al, 2006), The Grind is a local beauty spot and has been photographed repeatedly for over a century so that a photographic record exists to constrain the pattern and timing of block extraction and movement. This record also allows the surface discoloration of rock surfaces by weathering and lichen growth to be used as a relative indicator of their age and reveal the patterns and rates of erosion not only on the cliff top but also on the cliff face.…”

“…At sites where cliffs between 10 and 40 m high plunge into deep water, the platform or ramp of the upper cliff may carry boulder accumulations as part of a suite of cliff-top storm deposits (CTSDs) (Hall et al, 2006). CTSDs are mobilised only during storms and represent an important record of change on the cliff top and, where dated, provide an archive of information about past storms (Williams and Hall, 2004;Hall et al, 2006). This paper examines the processes and rates of marine erosion at The Grind of the Navir, an extremely exposed headland at Eshaness, in the west Mainland of Shetland (Fig.…”

Terrestrial Laser Scanner techniques in the assessment of tsunami impact on the Maddalena peninsula (south-eastern Sicily, Italy)

“…One of the most impressive evidence of extreme wave impact on the rocky coasts is represented by the presence of mega-boulders, sparse or accumulated in field or berms (Mastronuzzi andSansò, 2000, 2004;Williams and Hall, 2004;Hall et al, 2006Hall et al, , 2008Scheffers and Scheffers, 2006;Mastronuzzi et al, 2007;Scicchitano et al, 2007;Goto et al, 2009aGoto et al, , b, 2010a. The post-event surveys performed after the impact of the Indian Ocean Tsunami (IOT), occurred on December 26, 2004, have permitted to recognise morphological/sedimentological effects of its impact and, in the same time, to extend all obtained results on coastal sectors where similar evidences were recognised (e.g.…”