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British Volcanoes: Arthur's Seat, Edinburgh

As the ash cloud drifts this way and that around the North Atlantic - an ocean which owes its existence to the same forces responsible for Eyjafjallajökull itself - it’s time to pause and contemplate our own volcanoes again.

Last time we looked at the remains of the caldera on the Ardnamurchan peninsula, a volcano that may have been the result of the same hotspot as Eyjafjallajökull but is, in any case, related by virtue of its eruption at the start of the rifting process which first opened up the Atlantic.

This time we are concentrating on a more urban setting, on a volcano that last erupted in the Carboniferous period (between 360 and 290 million years ago) in the middle of what is now Edinburgh. It would have looked very different then, when much of Britain was a tropical swamp and a kind of prototype dragonfly flitted around the marsh with a two-and-a-half foot wing span; when arthropods which bear a resemblance to modern millipedes reached lengths of over eight-and-a-half feet; when all of this gigantism was made possible by an atmospheric oxygen concentration not far from double modern levels.

The view from the slopes of Arthur’s Seat

Around other parts of what is now the Midland Valley of Scotland, coal was being produced in the swamps of a coastal plain that was not unlike the northern shores of the Gulf of Mexico today (without the devastating oil-spill, of course). For 50 million years, this tranquil scene was occasionally interrupted by volcanic eruptions. First at what is now the Castle, then later in Holyrood Park, eventually forming the feature now known as Arthur’s Seat.

In the related volcanic activity that formed Salisbury Crags (below), however, the molten rock never actually made it to the surface as a volcanic eruption, cooling deep within the earth instead. By the way, if you live in London and don’t have a snowball’s chance in hell of getting to see Salisbury Crags or are simply too metropolitan to countenance travelling beyond the M25, the mountain has come to you instead. A lot of London is paved with it.
Salisbury Crags
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