Menai Strait
The Menai Strait is a strait which separates the island of Anglesey from Gwynedd, on the mainland of Wales. It is situated between Caernarfon Bay in the south-west and Conwy Bay in the north-east, which are both inlets of the Irish Sea. The strait is about long and varies in width from between Fort Belan and Abermenai Point to between Puffin Island and Penmaenmawr. It contains several islands, including Church Island, on which is located St Tysilio's Church.
The strait is bridged by the Menai Suspension Bridge, which was completed in 1826 to a design by Thomas Telford and carries the A5 road, and the Britannia Bridge a truss arch bridge which carries the North Wales Main Line and the A55 road; it is an adaptation of a tubular railway bridge completed in 1850 to a design by Robert Stephenson, which was severely damaged by a fire in 1970.
The differential tides at the two ends of the strait cause very strong currents which create dangerous conditions. One of the most hazardous areas is the Swellies, between the two bridges, where rocks near the surface cause over-falls and local whirlpools. This was the site of the loss of the training ship HMS Conway in 1953. Entering the strait at the Caernarfon end is also hazardous because of the frequently shifting sand banks that make up Caernarfon bar.
Origins
The present day channel is a result of glacial erosion of the bedrock along a line of weakness associated with the Menai Strait fault system. During a series of Pleistocene glaciations a succession of ice-sheets moved from northeast to southwest across Anglesey and neighbouring Gwynedd scouring the underlying rock; the grain of which also runs in the same direction. The result was a series of linear bedrock hollows across the region, the deepest of which was flooded by the sea as world ocean levels rose at the end of the last ice age.History
The name Menai comes from Welsh main-aw or main-wy, meaning "narrow water."According to Heimskringla, the 11th century Norse-Gael ruler Echmarcach mac Ragnaill plundered in Wales with his friend, the Viking Guttorm Gunnhildsson. However they started quarreling over the plunder and fought a battle at the Menai Strait. Guttorm won the battle by praying to Saint Olaf and Echmarcach was killed.
In the 12th century, a later Viking raid and battle in the Menai Strait are recounted in the Orkneyinga Saga as playing an important role in the life of Magnus Erlendsson, Earl of Orkney – the future Saint Magnus. He had a reputation for piety and gentleness. Refusing to fight in the raid on Anglesey, he stayed on board his ship, singing psalms. This incident is recounted at length in the 1973 novel Magnus by Orcadian author George Mackay Brown, and in the 1977 opera, The Martyrdom of St Magnus by Peter Maxwell Davies. The first of the opera's nine parts is called "The Battle of Menai Strait".
From the 1890s until 1963, the pleasure steamers of the Liverpool and North Wales Steamship Company would ply their main route from Liverpool and Llandudno along the Menai Strait, and around Anglesey. After the company's voluntary liquidation in 1962, P and A Campbell took over the services for a while. Now, every year for two weeks in the summer, the MV Balmoral undertakes a similar service. The most recent service appears to have been Feb-2021, since when the vessel has been taken to dry dock for essential repair work
Tidal effects
The tidal effects observed along the banks of the strait can be confusing. A rising tide approaches from the south-west, causing the water in the strait to flow north-eastwards as the level rises. The tide also flows around Anglesey until, after a few hours, it starts to flow into the strait in a south-westerly direction from Beaumaris. By this time, the tidal flow from the Caernarfon end is weakening and the tide continues to rise in height but the direction of tidal flow is reversed. A similar sequence is seen in reverse on a falling tide. This means that slack water between the bridges tends to occur approximately one hour before high tide or low tide.Theoretically it is possible to ford the strait in the Swellies at low water, spring tides when the depth may fall to less than. However, at these times a strong current of around is running, making the passage extremely difficult. Elsewhere in the strait the minimum depth is never less than until the great sand flats at Lavan Sands are reached beyond Bangor.
The tides carry large quantities of fish, and the construction of fish weirs on both banks and on several of the islands, helped make the Strait an important source of fish for many centuries. Eight of the numerous Menai Strait fish weirs are now scheduled monuments.
Ecology
Marine
Because the strait has such unusual tidal conditions, coupled with very low wave heights because of its sheltered position, it presents a unique and diverse benthic ecology.The depth of the channel reaches in places, and the current can exceed. It is very rich in sponges.
The existence of this unique ecology was a major factor in the establishment of Bangor University's School of Ocean Sciences at Menai Bridge, as well as its status as a special area of conservation with marine components. The waters are also a proposed Marine Nature Reserve.
Land
The same unique ecology and geomorphology has let to a number of designations of SSSIs along the strait including Glannau Porthaethwy, the ivy–oak–ash woodland on the southern shore and Lavan Sands. The banks of the Menai Strait are home to the critically endangered Menai Whitebeam. The plant is an extremely rare species of Sorbus only found in this part of North Wales. The population contains about 30 plants, and most of these are thought to be mature.Much of the land on Anglesey at the eastern end of the strait is designated as an area of outstanding natural beauty.