Discover Wales and Explore the Geodiversity and Fossils of Ynys Llanddwyn on Anglesey
- Wayne Munday
- May 5, 2025
- 4 min read
Updated: Jan 10
Ynys Llanddwyn, or Llanddwyn Island, lies off the southwest coast of Anglesey in North Wales and is celebrated for its striking geology, Celtic heritage, and romantic mythology. Part of the GeoMôn UNESCO Global Geopark, the island showcases mélange formations, pillow lavas, and stromatolites, some of the oldest fossils in England and Wales. It is also revered as the resting place of Saint Dwynwen, the Welsh patron saint of lovers, whose story is central to Welsh culture. Accessible on foot at low tide from Newborough Beach, Ynys Llanddwyn offers breathtaking views of Snowdonia and the Llŷn Peninsula. With its lighthouse, historic significance, and natural beauty, it remains one of Wales’ most enchanting and globally important geological destinations.
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.
