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30 Aug 2019

Stories from Staffa: island of staves

Written by Peter Upton, Visitor Services Assistant on Staffa
Eroding basalt columns by Fingal’s Cave, Staffa. The columns fall into the sea, which crashes against them.
Eroding basalt columns by Fingal’s Cave, Staffa
Staffa’s famous basalt columns and great caves have fascinated humans since ancient times. In this article I talk about the formation of this striking isle.

Until the late 1700s, Staffa’s extraordinary geology remained a largely local phenomenon. Undoubtedly impressive to all who saw it, its remoteness ensured that few outsiders knew of it. Then in 1772, the young botanist and scientist Joseph Banks went to investigate after hearing about it on his way to visit Iceland. Very quickly, Banks’s written descriptions of Staffa attracted others. It was challenging to reach Staffa and the western islands in those times. Arriving by rowing and sail boats took hours, and that was only after reaching Mull in days when roads were few and people travelled only by horse or on foot.

Staffa (staff-ay; island of pillars) was named by the Vikings, who were astonished to see an island apparently held up by a close mass of huge, regular sticks or staves. They believed the regular (mostly) hexagonal columns could not have been formed by natural forces, and must be the work of gods or giants. The striking similarity with the well known Giant’s Causeway in Ireland, just 82 miles south of Staffa, gave rise to stories of giants having built a roadway between the two lands. In fact, although the two features resulted from volcanism of approximately the same age (some 60–54 million years ago), the lavas that formed these basalts came from different volcanoes.

Staffa is formed of the lava that flowed from an eruption of the Mull volcano some 59 million years ago, long before humans evolved and around 7 million years after the great dinosaurs became extinct.

The volcanism of the whole region was due to an upwelling of hot mantle rock, known as a mantle plume. This plume is still active, but is now under – and still forming – Iceland. Around 60 million years ago, Scotland, Greenland and Labrador were close together and sat above this hot spot. Newly forming oceanic crust (the top layer of an oceanic tectonic plate) slowly pushed these zones away from the plume, both to the east and west. Now a long way from the heat, there’s no longer any volcanic activity in Scotland today.

In the intervening aeons, the Mull volcano and its surrounding lava flows have mostly been weathered away by sun, wind, rain, plant growth and, in the last 2 million years, ice. What’s often referred to as the Ice Age was actually just the most recent of several periods of global cooling, with repeated glaciation occurring. Millions of tonnes of ice and glaciers have worn down and erased large amounts of Mull’s volcano, and today we’re left only with eroded traces. Ridges of hardened basalt now remain where lava once filled the valleys of a warm and forested Palaeocene landscape on Staffa and the near-neighbouring Gometra – the softer ash and sedimentary rocks of the valley sides have long been eroded away. West of Staffa, the Treshnish Isles are another example of such a lava flow.

Staffa is the result of a particularly deep lava flow, probably the result of a blockage resulting in a deep lava lake. Thicker lava takes longer to cool, and slow cooling allowed the hardening basalt to shrink into the famous columnar forms exposed today. Erosion by ice and heavy ocean swells has reduced Staffa to the small island it is today, for of course the lava flow would have been much more extensive. Continuous battering by ocean waves has left us with the clean, sea-washed columns of Staffa’s Great Face. Erosion is relentless and every year, Staffa is a little smaller.

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