Trum y Ddysgl
Also within
Climate exposure
This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.
Coastal habitats are exposed to sea-level rise and storm erosion. Where hard sea defences sit behind them, there's nowhere landward to retreat to — a squeeze that keeps compressing the habitat no matter how well it's managed.
Geology & landscape
Geological Period: Cambrian, Ordovician · Rock Type: Quartzite
Landscape processes: Coastal, Glacial
Description
Description Trum y Ddysgl is of special scientific interest because it provides a rare example of overturning and thrusting of strata on the north-west limb of the Snowdon Syncline. The high intensity of deformation contrasts markedly with the lower strain seen farther to the north-east in central Snowdonia. The site is situated approximately 3 km west of Rhyd Ddu and lies to the north of the summit of Trum y Ddysgl (709 m) and incorporates a 1 km long cliff section which forms the south-western wall of a glacial cirque that opens northwards into the head of the Nantlle Valley. Trum y Ddysgl provides a superb section illustrating overturning and thrusting on the north-west limb of the Snowdon Syncline. The site consists of steeply dipping beds of the Upper Cambrian Marchlyn Formation which are thrust south-eastwards over Ordovician slates belonging to the Nant Ffrancon Group. Bedding/cleavage relationships and sedimentary structures in the Marchlyn Formation indicate that rocks at the base of the cliffs are slightly overturned. The structure is clearly illustrated by three prominent quartzite horizons. This section displays the more intense deformation which locally affects rocks in the south-western part of the Snowdon Syncline. In contrast to the open fold style around Capel Curig, folds are tight with slightly overturned limbs which, at Trum y Ddysgl, have been subsequently thrust towards the south-east. Remarks: The site lies within Snowdonia National Park.