The island of Staffa, with its amazing columns of basalt lava and the mythical Fingal’s Cave, is one of the most spectacular geological sights on the west coast of Scotland
The small Hebridean island of Staffa is the result of volcanic activity that occurred 60 million years ago during the early formation of the Atlantic Ocean. It is a classic symbol of Scotland’s geological heritage, and has inspired centuries of scientists, artists, poets and even classical composers.
Staffa would have been a distinctive landmark for the Vikings as they journeyed up and down the west coast of Scotland. The name ‘Staffa’ comes from old Norse, and means ‘stave’ or ‘pillar’ island, in homage to the incredible columns of cooled basalt lava that can be seen there.
The lava is underlain by a thin layer of volcanic ash. The lowest lava flow cooled slowly producing the most spectacular colonnade structures. These formed perpendicularly to the cooling surface at the base of the flow. Most of the columns are hexagonal, but five-sided and seven-sided columns can be found as well. The columnar structure is seen throughout the island but is at its most spectacular in the vicinity of Fingal’s Cave. In other places, the columns appear curved, or even horizontal. The lava flow erupted on an uneven palaeo-landscape, filling in valleys and hollows, so the cooling surface was not always horizontal. The neighbouring islet of Am Buachaille shows these curved columns well, as does the Clamshell Cave close to the jetty. The upper part of the flow forms an ‘entablature’ of highly variable jointing as the lava cooled more rapidly and irregularly from the top down, possibly through movement of water along cracks into the interior of the flow.
Underneath the lava flow, near sea level, there is a layer of volcanic ash that can be viewed at the inlet of Port an Fhasgaidh. This grey rock contains many large flattened fragments of lava, indicating that these projectiles were still molten when they landed in the ash.
Lines of weakness in the basalt have allowed the sea to gradually carve away caves in the island’s sides. The most famous is Fingal’s Cave; in Gaelic An Uamh Bhinn, ‘the Melodious Cave’. In the nineteenth century, James MacPherson’s Ossianic poetry made the island famous for its romantic connections with two warrior giants, one Scottish and one Irish – Fionn (or Fingal) MacCumhail. Legend has it that, to do battle with his foe, Fingal created a causeway to travel between Ireland and Scotland – the ends of which remain today as the Giant’s Causeway (a World Heritage Site) in Antrim, and, of course, Staffa.
Text contributed by James Westland
Find out more
Mull and Iona Geology: http://mullgeology.net/
Mull and Iona – a landscape fashioned by geology by John Merritt and Graham Leslie provides a great introduction to the geology of the wider area. Download from https://www.scottishgeology.com/find-out-more/publications/#northeast
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