Mountains have always been a source of wonder and are among the most spectacular features of the natural world. My Oxford English Dictionary defines a mountain as ‘a large abrupt natural elevation of the ground’ but that hardly does justice to the magnificence of the great mountain chains that are such a dominant feature of our planet and have been a magnet for mountaineers, geologists and tourists alike for centuries.
It is not obvious to the non-geologist why mountains exist, or why they are so high relative to the general ground level of the continents. As recently as 1935, the famous physicist Sir Harold Jeffreys believed, along with many geologists of that period, that the Earth was shrinking due to internal cooling, and that the horizontal forces produced by accommodating to the decreasing area of the Earth’s outermost shell were responsible for producing the great mountain ranges. Despite Alfred Wegener having promoted the theory of continental drift back in 1914, the contracting Earth theory was still widely held until the mid-twentieth century. Moreover, it may not be apparent why the great mountain ranges occur where they do, as distinct linear features, rather than being randomly distributed across the continents. It was only in the 1960s that plate-tectonic theory at last gave us a plausible mechanism for the formation of mountain belts.
The most obvious mountain chains today, such as the Himalayas, the Alps and the Andes, are situated at currently active plate boundaries. Others are the product of a plate collision that happened far back in the geological past, and have no present relationship to a plate boundary. These are much lower, with a generally more gentle relief, worn down through millennia of erosion by rain or ice. Many mountains are formed entirely by volcanic activity and, although also found along plate boundaries, frequently occur singly or in small groups. The most impressive of the volcanic mountains are almost completely hidden, forming the great ocean ridges that rival the Himalayas in scale.
The purpose of this book is to take the reader on a geological tour through the world’s great mountain systems, examining in each case the plate-tectonic processes thought to be responsible for their evolution. The book is not intended as a comprehensive description of the geology of the Earth’s mountains, which would be impossible in a single volume, but, in providing a general overview of the main mountain systems and their plate-tectonic contexts, it is hoped to reveal their grandeur and complexity, and the ingenuity of the mechanisms that have been advanced to explain them.
Graham Park, 2017
Acknowledgements
I am indebted to Professor John Winchester for many helpful comments and suggestions that have resulted in significant improvements to this book, and to my wife, Sylvia, for her unfailing support and for checking the manuscript for general readability.