Erupting Volcanos

The next major geological event was to be literally explosive. The opening up of the north Atlantic, a process continuing today, was accompanied by widespread volcanic activity. Scenes similar to those in present day in Iceland, produced a great basalt plateau, the eroded remains of which dominate Antrim and parts of Londonderry.

During the early Tertiary period successive lava flows covered the land, sometimes producing dramatic landscapes as at the Giant's Causeway, while some molten bodies failed to reach the surface but have been exposed by subsequent erosion. These have often resulted in striking features and include Fair Head and Ramore Head on the north coast. Elsewhere combinations of surface volcanic action and intruded molten magma resulted in the formation of the Slieve Gullion complex with its remarkable 'Ring', while Tardree hill in Antrim is the result of surface volcanic activity alone. Mention must also be made of the Mountains of Mourne which were formed at this time as molten granite was emplaced just below the land surface and now exposed by erosion.

This widespread volcanic activity was accompanied and followed by frequent shifts in the relative levels of the land. This faulting, often reactivating much older crustal weaknesses, has produced a range of features. Large scale faulting over the central area of Northern Ireland resulted in a basin, now occupied by Lough Neagh. Elsewhere, faulting has often brought rocks of different ages to similar levels so that cliff scenery on the north coast shows dramatic lateral transitions from basalt to chalk.

Lough Neagh and other basins acted as a natural sink for accumulating sediments during the latter part of the Tertiary. There has been much interest in these rocks as, along with the mud and sand, much organic material, especially wood, was also deposited, forming lignite. This brown coal may be exploited in the future, around southern Lough Neagh and also at Ballymoney.