Discover Wales and Explore the Geodiversity and Fossils of Ynys Llandwyn on Anglesey
- Wayne Munday
- 31 minutes ago
- 4 min read
Sip back and discover North Wales and explore Ynys Llanddwyn or Llanddwyn Island on the south west coast of Anglesey or Ynys Môn in Welsh. As well as a place of rugged beauty, rich Celtic history, and captivating coastal charm Ynys Llanddwyn is also a significant global geological site within the GeoMôn UNESCO Global Geopark and the resting place according to Welsh mythology or Y Chwedlau of Saint Dwynwen - Llanddwyn means Dwynwen’s Church. Renowned for its unique and chaotic rock formations known as mélanges that extends through the Llŷn Peninsula onto Bardsey Island. This tidal island was where the term mélange (meaning mixture) was first coined in 1919 by British geologist Edward Greenly to describe a disorderly and different mix of rock types formed under intense deformation commonly found in tectonic subduction zones. Ynys Llanddwyn exposes a mix of limestone, cherts, and pillow lavas that reflect the turbulent tectonic processes from the formation, movement and subduction of the oceanic crust dating from the Late Neoproterozoic to Cambrian Period. The limestone of Ynys Llanddwyn preserves stromatolites or microbial reefs created by cyanobacteria the oldest fossils in England and Wales dating back over 860 million years. Ynys Llanddwyn ranks among other mélanges including the Franciscan Complex in California's Coast Ranges, the Bay of Islands ophiolite complex in Newfoundland and the Northern Palawan Mélange in the Philippines as indicators of past tectonic events, plate interactions and ocean floor geology.
Anglesey is a must-visit destination for travellers seeking both tranquillity and adventure in North Wales. Connected to the mainland by the iconic Menai Suspension Bridge and the Britannia Bridge. Anglesey's appeal lies in its contrasts and over 220 miles of coastline navigated by the Anglesey Coastal Path. It’s a wild yet peaceful, remote yet accessible, ancient landscape.
Whether you're kayaking through sea caves, discovering the Bronze Age and Neolithic period standing stones of Castell Bryngwyn, Penrhos Feilw, Llanddyfnan or the Neolithic burial chambers like Bryn Celli Ddu or visiting Beaumaris Castle the last royal strongholds created by Edward I in Wales or simply enjoying the silence of a sandy beach at dawn like Newborough Beach and National Nature Reserve. Anglesey offers a journey through one of Wales’ most magical landscapes.
One of the most enchanting places on the island of Anglesey is Ynys Llanddwyn a tidal island accessible by foot during low tide from Newborough Beach with sweeping views of Eryri National Park or Snowdonia and the Llŷn Peninsula an Area of Outstanding Natural Beauty. This is a stunning stretch of land with its historic lighthouse known as a Tŵr Bach or Small Tower was originally built to guide ships into the Menai Strait.
Ynys Llanddwyn is thought to have been the home and resting place of Saint Dwynwen the Welsh patron saint of lovers and has long been a romantic and spiritual site. St Dwynwen's Day is celebrated on the 25th January and is the Welsh St Valentine’s Day though the myth tells of a tragic love story.
Saint Dwynwen was a 5th-century princess and daughter of King Brychan Brycheiniog of South Wales who was known for her beauty and kindness, Dwynwen's fell in love with Maelon Dafodrill a Welsh nobleman. The King forbade their union and she prayed for help receiving a potion from an angel that made her forget Maelon though it unfortunately turned Maelon to ice. Granted three wishes by God she asked for Maelon to be thawed and for God to help all true lovers and she swore herself never to marry. She spent the rest of her life as a nun.
For somewhere that is recognised for its global importance as a geological site Ynys Llanddwyn is comparatively modest in size measuring approximately 300 by 700 meters. The island is primarily composed of rocks from the Gwna Group also known as the Bodorgan Formation and lays between the high-angle fault zones that separate it from the surrounding Blueschist Unit to the east and the Carboniferous Limestone in the west.
Ynys Llanddwyn exposes an exceptional sequence of Oceanic Plate Stratigraphy (OPS) offering insight into subduction processes and mélange formation. Oceanic Plate Stratigraphy describes the layered sequence of rocks formed on oceanic floors as it ages, moves across ocean basins and approaches subduction zones. This sequence captures the geological history from its creation at the mid-ocean ridge to its destruction at trenches and is organised into several staged imbricated units called “horses" separated by faults.
Oceanic Plate Stratigraphy typically follows a vertical progression starting with Mid-Ocean Ridge Basalts (MORB). The basaltic rocks are often pillow lavas formed at spreading centers and at the base of the OPS. Ynys Llanddwyn is especially recognised for its well-preserved mid-ocean ridge basalt pillow lavas formed in the deep ocean and are indicative of deposition on or near a spreading ridge and subsequent subduction zone.
The pillow lavas exposed at Ynys Llanddwyn are typically between 30 - 60 cm in diameter and visibly exhibit chilled margins or have a fine-grained glassy igneous outer edge formed when hot magma rapidly cools upon contact with a cooler medium such as air, water or a surrounding rock.
Another prominent feature of Ynys Llanddwyn is the presence of a large-scale duplex formed by the compression of tectonic forces where multiple thrust faults have stacked slices imbricates or horses.
