Blueschist at Marquess of Anglesey’s Column
Blueschist at Marquess of Anglesey’s Column is a very rare rock at a stunning location. For more than 200 years the Marquess of Anglesey’s Column has been a striking landmark on the skyline along the Menai Strait, allowing visitors to climb the 115 steps to the top and enjoy panoramic views of Anglesey, the Menai Strait and Snowdonia. The Column is constructed of local Carboniferous limestone and sits on Craig y Dinas, a prominent outcrop of the world-renowned Precambrian Anglesey blueschist.
The site closed in 2014 due to safety concerns but ambitious plans were drawn up and a campaign was started to seek funding to restore the Column and develop a World-class visitor attraction.
The site also includes the Marquess of Anglesey’s Column GCR site, which is one of three individual areas of blueschist making up the Sgistau Glas Ynys Môn SSSI. The GCR site includes natural outcrops around the base of the Column
What is blueschist?
Blueschist is a distinctive type of metamorphic rock that has a unique mineral assemblage, which reflects specific pressure and heat conditions during the metamorphism of basalts and mafic rocks. Typically, blueschist is formed by the subduction and rapid burial of oceanic crust (including, in this case, pillow lava) where cold rocks are buried quickly and thus subjected to high pressure and relatively low temperature. The conditions for blueschist formation are normally found at a depth of some 30-50km in the Earth’s crust.
GeoMôn have been monitoring the site for many years because of the importance of the blueschist and havedesignated parts of the exposure as RIGS sites,
Further opportunities will also come from increased collaboration with GeoMôn. Geological-specific support for interpretation will be developed over the coming years and will cement the Column as one of GeoMôn’s flagship geosites. GeoMôn has already been documenting some of the new exposures revealed at the Column as part of a wider project investigating other Anglesey blueschist outcrops and the relationships between structures and mineralogy in these severely deformed rocks.
Read the whole earth Heritage issues Earth Heritage magazine number 62