GEOLOGICAL HISTORY OF THE GIANT’S CAUSEWAY

The story of the Causeway landscape begins between 62 million years ago with an episode of extensive volcanism linked to the opening up of what is now the Atlantic Ocean. Although there is some evidence of early explosive activity associated with volcanic vents, for at Carrickarade, some 10km east of the Causeway, the period was dominated by multiple of basalt lavas. The total area of these flows is now much reduced compared to their original extent, but they still constitute, at 3,800km2, Europe’s most extensive lava field. Traditionally the lavas of the Antrim Lava Group have been divided into three main phases of activity, separated by two extended periods of quiescence or limited, local activity.

During these intervening periods the upper surfaces of the preceding flows were exposed to climatic conditions that were both warm enough and wet enough to weather the rock to a depth of several metres. This produced soils and weathered regoliths that are redolent of those found in the present-day Humid Tropics and which appear today as two, largely red coloured, ‘Inter-basaltic Beds’ separating the Lower, Middle and Upper Basalts. The landscape of the World Heritage Site is cut into the Lower and Middle Basalts and the lower of the two Inter-basaltic Beds.

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Cliffs near Port na Spaniagh. Both Lower and Middle Basalts and the interlayered palaeosol are distinguishable.

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