Volcanoes and the Making of Scotland

Upton Brian

Description

Scotlands mountains and glens retain the secrets of the long and frequently violent geological history that has gone into their making. Volcanoes have played a major role in the creation of Scotland and while the youngest, a mere sixty million years old, were responsible for much of the scenic splendour of the Inner Hebrides, the rocks composing many of the famous Scottish landforms as, for example, those of Glencoe and the Edinburgh district are also the direct result of volcanism.Volcanoes and the Making of Scotland explores back in time from the most recent examples to volcanoes of the obscure Precambrian times which left their signature in the ancient rocks of the far north-west. Geographically the book ranges across all of Scotland from Shetland to the Borders. Reflecting current research into Scotlands geology, the author also speculates as to the climate, geography and ecology of the long-gone landscapes in which the volcanoes of differing ages were created and destroyed.The book is extensively illustrated with maps, sketches, cross-sections and photographs and relates what can currently be seen in the worn-down remains of Scotlands old volcanoes to active analogues around the world. This book vividly brings life and meaning to what the layman would otherwise regard as cold and incomprehensible rocks.

Sujets

• Sciences et techniques
• Escocia
• Reference
• Historical geology
• Scotland

Informations

• Publié par: Dunedin Academic Press
• Date de parution: 01 octobre 2015
• Nombre de lectures: 0
• EAN13: 9781780465418
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Volcanoes and the Making of Scotland
Second Edition
Brian Upton
Emeritus Professor of Petrology and Senior Honorary Professorial Fellow, University of Edinburgh
DUNEDIN
EDINBURGH ♦ LONDON
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Contents
       Foreword
1     Introduction
2     Time on Earth and a Brief History of Scotland
3     Magmas and Igneous Rocks
4     Lava Flows and Pyroclastic Deposits
5     Paleocene Fissure and Shield Volcanism in the Hebrides
6     Hebridean Paleocene Volcanoes: the Big Ones
7     Scotland within a Super-continent: Upper Carboniferous and Permian Volcanoes
8     Post-Caledonian Relaxation: the Lower Carboniferous Volcanoes
9     Volcanoes of the Old Red Sandstone Continent
10   Volcanoes and the Iapetus Ocean
11   Descent to the Dark Ages: Volcanic scenes from the Precambrian
12   Epilogue
       Select Bibliography
       Index
Poetry in stone! A natural staircase of basalt lava, Staffa.
Foreword
There have been so many times during my geological travels in Scotland when I have met farmers, fishermen, tourists and others who have been curious about what I was doing and who have asked me to explain, in simple terms, the origin of the rocks and landscape features around them. Having spent a professional lifetime publishing papers for scientific readership as well as teaching, almost exclusively, to geology students in one of Scotland’s oldest universities, I felt it time to attempt to write a reasonably non-technical explanation for the general public. My own work, which has been devoted to volcanology and igneous petrology over the past 55 years, has afforded me the privilege of working in areas of active or recent volcanism as far apart as Iceland, East Africa, the western Indian Ocean and the United States.
Whilst Scotland may lack active volcanoes, its landscape is crowded with the rocky outcrops providing evidence of volcanoes that erupted in bygone ages. Scotland is probably more richly endowed with the relics of volcanic eruptions than any other tract of comparable area on the face of the Earth. These cover a time span from nearly 3000 million years to the relatively recent past at around 60 million years (or as recently shown, to around 46 million years). The volcanic products that contribute to its geology can be shown to represent just about every type of volcano known. Many of its well-known topographic features represent the root zones of volcanoes, the upper parts of which have been shaved off by erosion. This is true for some of the well-known topographic features in central Scotland such as Dumbarton Rock near Glasgow and Castle Rock, Edinburgh, as well as for many of the most scenic parts of the Hebrides and western Highlands. In general, the rocks from which the Scottish landscape has been sculpted record a long and complex history of events in which volcanism has played a major role.
Had this account been intended as a scientific treatise it would be littered with references to relevant works and there would be a long listing of all those publications that I have consulted. But it is not, and at the end I refer only to a selection of sources that provide a lead to those readers looking for more detailed information. In writing this book I have helped myself very freely to material from the published literature. I am conscious of the huge debt of gratitude I owe to all who have taught me about the igneous rocks of Scotland over the past sixty plus years. Without the encouragement of Gordon Craig and Douglas Grant the book would never have started. Among those others who have given specific help my sincere thanks go to Brian Bell, Anne Burgess, Euan Clarkson, Henry Emeleus, Rhona Fraser, Bill Gilmour, Peter Kokelaar, Graham Leslie, Ray Macdonald, Alastair Robertson, Jack Soper, David Stephenson and D. Troll for their time and wisdom. To any who may feel that I have misrepresented their ideas or conclusions, I ask forgiveness. My heartfelt thanks also go to Yvonne Cooper and Melanie Upton for technical help. It is difficult to find appropriate words of thanks for my wife, who has shown patience beyond the call of duty while the book was being written.
Ekkehart Màttig, Senckenberg Museum of National History Görlitz
Chapter 1
Introduction
Scotland today presents a peaceful landscape. Earthquakes are rare and mercifully small, and the nearest active volcanoes lie far to the north-west in Iceland, or away to the south-east in Italy. Admittedly we do not have to travel quite so far to see landscapes that are easily recognizable as volcanic; in central France the Chaîne des Puys consists of volcanic hills that have been little modified by erosion since they last erupted several thousand to tens of thousands of years ago. The Romans, who recognized them as old volcanoes, were, of course, thoroughly familiar with such features at home. The Eifel district in western Germany, like the Chaîne des Puys, remains a potentially active volcanic region. Scotland, however, is volcanologically inert, offering no possibility of an eruption at least within the next few millennia. And yet a record of volcanism over a huge period of geological time is preserved in the Scottish rocks, and this book attempts to present a guide for students and amateur geologists to Scotland’s dramatic and fiery past. Evidence of the former existence of volcanoes, in more or less ruinous and fragmentary state, is to be seen scattered in a thousand sea-cliffs, road-cuts, quarries, hillsides and mountains from Shetland to the English border.
Although there is general public awareness that Scottish landscape features such as Arthur’s Seat, Staffa, Glencoe and the Cuillins are of volcanic origin, there is a conceptual difficulty in relating what one actually sees to the perception of an active volcano. Nowhere does one actually see a volcano, just their relics. If a city had been destroyed by earthquake or war almost every building might have been flattened and the rubble removed and yet, from the basements, foundations and plumbing, an archaeologist might well be able to reconstruct a tolerable picture of what it had been like. In Scotland, whilst the lavas might be clearly seen, the old volcano constructs are invariably destroyed, and it is from their foundations, together with knowledge of recent and active volcanoes, that the volcanologist and igneous petrologist can piece together a model of the former volcano.
Terminology is one of the main stumbling blocks. Lack of understanding of the relationship between intrusive igneous rock bodies formed within and beneath volcanoes and the extrusive phenomena with which they may have been associated is another. This book is written as a non-technical account of the volcanic history of Scotland. In general, the older the volcanic rocks the more the accidents and crises throughout geological time (e.g., faulting, folding and erosion) have made the obvious links between their outcrop and a modern volcano ever more tenuous. Consequently, whereas it is traditional in geology texts to start with the oldest rocks and work ‘upwards’ towards younger formations, I am deliberately reversing this convention. I shall start with the youngest rocks and go back in time to features in the oldest rock formations that date from roughly 3000 million years ago. It is easier to understand how features such as the Cuillins, a mere 58 million years old, might represent the sawn-down ruins of a once great volcano than it is to try to do the same with, for example, a much older and highly contorted suite of volcanic rocks such as are seen on the south-west coast near Ballantrae. It is consequently my intention to tell history backwards, inviting the reader to join me in my metaphorical time-machine to consider the origins of the remarkable variety of volcanic rocks that contribute to the Scottish landscape. This account of the ancient volcanoes is intended neither as an academic treatise nor as a field guide. My choice of volcanoes is to a large extent idiosyncratic while, at the same time, including the better known topographic features such as Ben Nevis, Glencoe and Castle Rock (Edinburgh) that are of volcanic origin.
The tectonic plate (or plates if we go back far enough) within which the Scottish rocks formed have, as a generality, migrated on a northerly journey from polar latitudes far south of the Equator to their current position in the northern hemisphere. Thus, if we are considering the more recent evidence (from the Hebrides), we must think of these being some hundreds of kilometres further south, in a distinctly milder climatic zone. I write here of plates ‘migrating’. It is of critical importance to bear in mind that things are not now as they were then. With the passing of time, the geography of the world changes. Just in the past decade, for instance, as a consequence of the earthquake responsible for the December 2004 tsunami, the map of parts of the Indian Ocean, like the coastlines of the Nicobar and Andaman Islands off the Burmese coast, changed irrevocably. On average, the plates move (and change shape) only by millimetres per year, so that over a thousand years the Atlas maps change a little. Over ten million years, however, they change quite a lot. In this b