BBC News Science and Environment
5 July 2012 Last updated at 02:09
How volcanoes shaped Britain's landscape
Glen Coe in the Highlands of Scotland is the remains of an ancient supervolcano that erupted about 420
million years ago
Britain's volcanic fires may be no more, but remnants of an enduring eruptive past can
be found throughout the country, writes Professor Iain Stewart.
"So there I lie on the plateau, under me the central core of fire from which was thrust this
grumbling grinding mass of plutonic rock, over me blue air, and between me the fire of the rock
and the fire of the sun, scree, soil and water, moss, grass, flower and tree, insect, bird and
beast, wind, rain and snow - the total mountain."
Those words - from Nan Shepherd's recently resurrected gem The Living Mountain (Canongate)
- perfectly evoke the intimate relationship between the flora and fauna of upland Britain and its
ancient volcanic past.
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Professor Iain Stewart and Kate Humble present Volcano Live - starting on BBC Two
on Monday 9 July at 20:00 BST
In this case, the reverence is for the rounded granite bulk of the Cairngorm mountains in northeast Scotland, but across Britain and Ireland rocks born molten many millions of years ago still
fashion the familiar natural world around us.
The Cairngorms themselves are the roots of mountains that formed about 420 million years ago
when a great seaway separating the rocks of Scotland and Northern Ireland from those of
England and Wales crumpled shut.
During the final death throes of that ancient Iapetus Ocean, a chain of explosive volcanic islands
had lined the leading edge of the approaching southern landmass of Avalonia - today the jagged
highlands of Snowdonia and the Lake District are the ice-sculpted remains of that once fiery
frontier.
When Avalonia finally collided with the Celtic fringes of the northern landmass (Laurentia), a
mountain range of Himalayan stature was thrown up.
“Even amid the lowlands of middle England, volcanic fires once burned”
Molten rock (magma) that had readily risen to fuel surface volcanoes now congealed in the
depths of the over thickened crust, investing the lofty peaks with granite hearts.
Erosion has now exhumed these granite cores, exposing them in the alpine plateaus of the
Cairngorms, and further west, in the boggy bleakness of Rannoch Moor.
So in Britain you do not walk on volcanoes, you walk within them. Take our highest mountain Ben Nevis. Few of those that take the sturdy hike to its summit probably appreciate that they are
journeying through the innards of a disembowelled volcano.
Moreover, it is one that met with a truly cataclysmic end. The clue is found near the summit,
where light coloured granite that had cooled in subterranean chambers several kilometres down
now lies right up against dark basaltic lavas that once spewed out at the surface. Ordinarily
never the twain shall meet.
The fact that today they are found side by side implies that the huge ancient volcano collapsed
in on itself. The event, which occurred some 350 million years ago, was of such epic violence
that it is almost impossible to imagine today.
Ben Nevis was a large and active volcano which eventually exploded and collapsed inwards
To approach anything close you have to leave the bens and glens behind and transport your
imagination thousands of miles eastward to the infamous blast in 1883 that ripped the heart out
of Krakatoa volcano, west of Java.
Or back several millennia to the even larger Bronze Age eruption of Thera volcano (modern
Santorini in Greece) which wiped the Minoan culture off the face of their Aegean heartland.
Over hundreds of millions of years, such extraordinary volcanic actions have laid the foundation
for our natural landscape. The signs are all around, if you know what to look for.
In Edinburgh, clamber up to the top of Arthur's Seat - its cliffs a sheet of solidified magma - and
you can see isolated rocky pinnacles scattered along the Forth estuary, each the eroded neck of
a former volcano.
Or venture west to the Campsie Fells, where the same magma-fuelled maelstrom 300 or so
million years ago built a magnificent staircase of lava flows that today rise above Glasgow.
Even amid the lowlands of middle England, volcanic fires once burned - the gentle summits
above Church Stretton in the Welsh borderland, for instance, are the outpourings of 600 million
year old lavas.
Etna is the highest active volcano in Europe
Of course today, those long enduring volcanic fires are extinguished. The last hurrah of the UK
volcano was about 55 million years ago, when an extraordinary fiery outburst accompanied the
wrenching open of the North Atlantic ocean. All along what is now the western shores of
Scotland, huge volcanic centres erupted colossal quantities of magma. The islands of Arran,
Mull and Skye are among the remains of a chain of volcanoes that draped much of northern
Britain and Ireland in enormous amounts of lava and volcanic ash.
Deeper fracture lines radiating out from these centres injected Hebridean magma as far south
as the North Sea coast of Yorkshire, travelling the 400km in something like five days! But such
volcanic violence was not to last. Over millions of years, the spreading of the Atlantic seaway
shunted eastward Hebridean volcanoes away from the well of superheated rock that originally
fed them, so that, today, that upwelling now feeds the craters and geysers of Iceland.
With the demise of our home-grown volcanoes, it is to the likes of Iceland and Italy that we must
now travel to see our closest live volcanic action. Many UK scientists study active volcanoes in
those areas, as well as further afield in the Caribbean islands or around the Pacific Ring of Fire.
But UK volcanologists do so armed with an intimate knowledge of our own volcanic heritage
which, exposed by millions of years of erosion, reveals the deep "plumbing" of once active
volcanoes. That is important because volcanoes are far more than just spectacular firework
displays. They are also geological windows into our planet - portals that allows geologists to
delve deep into how the Earth works.
Professor Iain Stewart and Kate Humble present Volcano Live, from Kilauea on Hawaii, the
world's most active volcano. Starting on BBC Two on Monday 9 July at 20:00 BST.
Reference
BBC (2012) How Volcanoes shaped Britain’s landscape ‘http://www.bbc.co.uk accessed 11/07/2012