The shore platform and stack at The Gegan
Paper on boulder size and storm wave velocities
Sketch of the shore platform
Q wave quarry zone
Imbricate cluster of large boulders on the shore platform. The white flecks are calcite crystals. These blocks do not appear to be present in air photos from 1952 but are present in 1985. Were the blocks transported in the 1953 storm in the North Sea?
Video shot on 30/03/2010 when the Spring Tide coincided with a north-easterly gale, allowing a rare opportunity to observe wave activity on a shore platform
Significance: an exposed shore platform with large wave-transported blocks
The Gegan is a small stack created from the erosion of a headland. At its foot stands a shore platform raised a few metres above sea level. There are many signs that modern wave erosion is quarrying large blocks from the seaward edge of the platform and transporting them across the platform.
The stack and platform are developed in red-brown, bedded, coarse-grained agglomeratic tuffs with bombs of basalt and mugearite. Blocks of marl and limestone are also present. The tuffs are cut by joints, with calcite veining and sedimentary dykes (Davies et al., 1985). On higher parts of the platform the bombs and veins have weathered out to stand up to 30 cm proud of the surrounding surface.
A striking feature of the platform is the presence of imbricate clusters of large blocks of agglomerate. These blocks can be traced to quarry zones in the thick landward-dipping beds that form the seaward edge of the platform. The blocks are large - up to 3.7 m in a axis length. Some have been eroded and transported quite recently, as fracture surfaces retain fresh calcite crystals.