Giant’s Causeway (Part 2): Other volcanic highlights

Dr Trevor Watts (UK)

This is the second and final part of an article on the volcanic highlights of Northern Ireland’s Giant’s Causeway and surrounds. We were in the area for several days and the weather was fairly mixed, but there were glorious skies between the showers, and the high winds brought the waves up beautifully. Of the six highlights discussed below, we visited the first three in one day, as all were a few kilometres to the west of The Giant’s Causeway. Those to the east, we visited on another day.

They are all supremely interesting and give an idea of the range of volcanic features to be seen. You cannot see an actual, traditional volcano in Antrim, with its classic shape. However, you can visit many scattered and varied elements of the area’s vulcanicity, and so gain an appreciation of the overall picture.

1. Cross section highlights final
Fanciful cross section of highlights. 1. Deep lava flows forming the Causeway Basalts and their columnar basalt features. Found at The Giant’s Causeway and Ballintoy Harbour. 2. Beds of red ‘laterite’ rocks and soils buried by the later lava flows. Seen along the whole coast, especially east of the Giant’s Causeway. 3. Multiple relatively thin lava flows forming the Lower Basaltic Series. Seen at The Giant’s Causeway area and Dunluce Castle. 4. Dykes bringing magma towards the surface through fissures of cracks in the country rock. Such as The Camel’s Back and others near the Giant’s Causeway. 5. Sills spreading magma fairly horizontally between layers of country rock, some thick and columnar. Ramore Head, Knocksoghy Head and Sheep Island are good examples. 6. Country rock that has been altered (metamorphosed) by the nearby volcanic heat and/or pressure. Well seen at Ramore Head. 7. Minor, as well as major, volcanic necks bringing magma upwards to volcanic cones and other surface features. Excellent examples along the low cliffs at White Rocks Beach, Kinbane Castle and Carrickarede. 8. Volcanic necks where the surrounding rocks have been shattered by the force of the eruptions, often causing material to fall back into the volcano’s throat. These can be seen at Kinbane Castle and in some of the volcanic ‘throats’ along White Rocks Beach. 9. Pyroclastic fragments and ash, sometimes as a covering over earlier landscapes and sometimes re-filling open volcanic necks. At Kinbane Castle and White Rocks Beach. 10. Thin lavas and agglomerates where other rubble has been caught up and moved by flowing lava or mud. Good examples at Kinbane Castle and White Rocks Beach.

The volcanic sill at Ramore Head, Portrush (about 13km west of the Causeway)

This is different to a lava flow because the magma was forced between layers of rock and not just spread over the top of them. There is easy parking and a well-made footpath around the peninsula, with good views of the irregular columnar jointing. There is one long, narrow inlet, perhaps 30m long by a couple of metres wide, which appears to have been formed where a dyke of softer material has been eroded away. Beneath the walls of dolerite, there is the country rock into which the magma was intruded: Lias shales. These are heavily metamorphosed and jointed in places, but they contain an abundance of ammonites in others. We didn’t find any, but we didn’t look very hard. However, there are many birds – herring gulls, terns and oyster-catchers aplenty – along with a smart playground for children and a very welcome cafe on a rainy day.

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