Bertra Strand is located on the southern shore of Clew Bay and connects the mainland to Bertra Island. This beach is a large crescent shaped shore with a sandy substrate. The strand at Bertra can be described as a ‘tombolo’, (a word derived from the Latin ‘tumulus’ meaning mound) which is defined as a landform where sand is deposited in a narrow connection between the mainland and an island.
Clew Bay is an area of international scientific importance due to its geomorphical significance as one of the few DROWNED DRUMLIN landscapes in the world. Drumlins are low, elongated hills composed of glacially deposited materials and usually occur in fields or “swarms”. Their shape indicates the direction of ice flow with the steeper, blunt end facing the direction from which the ice came. The Clew Bay field was submerged when the ice caps melted, causing the sea level to rise. The western-most drumlins have been almost completely eroded by the force of the Atlantic waves. The outer drumlin islands have steep seaward facing cliffs of boulder clay but much of the eroded material has been redeposited in the form of shingle spits, tombolos and forelands. Some of these spits link the western islands to create a distinctive coastal pattern and protect the inner drumlin islands from the Atlantic waves.
Sand carried inland by onshore winds is deposited in streamline form around some obstacle. Plants then colonise these small mounds of sand. As sand deposition proceeds, their foliage creates even more deposition and the root network binds the sand into low embryo dunes. As these dunes grow in height they merge parallel to the shoreline. In turn they are colonised and stabilised by other establishing plants and the dunes continue to grow.
Almost all dunes are subject to erosion, most commonly caused by “blow outs”. This happens when the wind gains access to sand beneath the vegetation at the crest and rapidly erodes the surface causing a depression. As the wind is channelled into it, the depression grows until its width reduces the channelling effect of the wind, leaving low-lying rolling dune pasture called Machair.
Frontal erosion occurs when the entire seaward face of the dune system is cut down by storm waves. This can be recognised by a steep slope of loose sand and slipping clumps of crestal vegetation. Human activity also has a large part to play in dune erosion. The removal of sand and shingle can eave large areas of dune open to wind erosion. Cutting dune vegetation or over-grazing the area by cattle or horses is another damaging activity. Recreation at beaches can also damage dunes. Vehicle movements can damage the turf carpet and the creation of paths through the dunes exposes bare sand where blow-outs can occur.
Waders such as the Snipe, Lapwing and Oystercatcher are frequently spotted in this area.
The Gull family is well represented with the Common Gull, Kittiwake, Blackheaded Gull, Great Black-backed Gull, Lesser Black-backed Gull and Herring Gull all visitors to the beach.
Lesser Black Backed Gull
Terns are also sighted with the Arctic Tern, Common Tern and Sandwich Tern being the most commonly noted.
Cormorants and Shags have also some of the more common birds to visit this beach.
|Arctic Tern||Sandwich Tern|
Bertra Beach Legend Map
Mayo County Council
Phone: (094) 9024444
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