Description Origins Distribution Zonation The Carran Turlough Environmental gradients Turlough Flora Multivariate Analysis Bibliography Links Turloughs & Burren Multivariate Analysis

Turloughs are seasonally dry lakes. They occur over the glacially modified carboniferous age limestones of central and western Ireland. They fill and drain with water, through a series of sink holes and fissures in the turlough floor, often with filling extreme rapidity. Whilst turlough margin vegetation shows a distinct zonation from wet to dry, turlough margins are characterised by their rapidly fluctuating water levels.

Turloughs are formed in bedrock hollows, although they may be floored with glacial deposits. Glacial deposition is a major controlling factor on the extent and shape of turloughs. Turloughs are a glacio-karstic feature of a hydrologically complex, largely depositional, landscape.

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Three theories for the origins of turloughs have been proposed, (from Coxon, 1986) ;

• The zone of higher permeability was developed post-glacially.  At times of high water input to the system water is forced upwards into topographic lows along the route which resulted in the formation of turloughs.

• Extensive solution in the tertiary resulted in the creation of a karstic landscape with a well developed subterranean drainage network.  Repeated glaciations removed many of the surface karstic features and partly clogged the underground drainage system with glacial deposits.  Glacial erosion and deposition created a new surface topography. Following the retreat of the ice the partly blocked flow route was unable to cope with any high water input to the system, and forced water to the surface, resulting in temporary ponding in depressions above the flow route.

• Glacial processes did not completely destroy the karstic landscape that developed in the tertiary but modified them by erosion and deposition. The underground drainage network associated with the karstic features became clogged with drift. Following the retreat of the ice, water entering the aquifer through the drift tended to follow pre-existing drainage lines. At times of high water input, excess water would be forced from the inefficient flow routes to the points corresponding to the original closed depression through the pre-existing karstically formed conduits.

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Darrel Watts

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