The Ice Age

Jürgen Ehlers, Philip Hughes, Philip L. Gibbard

• Publisher: Wiley-Blackwell
• Year: 2015
• ISBN:
  9781118507773
• Edition: 1
• Topic: Ciencias físicas
• Subtopic: Geología y ciencias de la Tierra

This book provides a new look at the climatic history of the last 2.6 million years during the ice age, a time of extreme climatic fluctuations that have not yet ended. This period also coincides with important phases of human development from Neanderthals to modern humans, both of whom existed side by side during the last cold stage of the ice age. The ice age has seen dramatic expansions of glaciers and ice sheets, although this has been interspersed with relatively short warmer intervals like the one we live in today. The book focuses on the changing state of these glaciers and the effects of associated climate changes on a wide variety of environments (including mountains, rivers, deserts, oceans and seas) and also plants and animals. For example, at times the Sahara was green and colonized by humans, and Lake Chad covered 350, 000 km2 – larger than the United Kingdom. What happened during the ice age can only be reconstructed from the traces that are left in the ground. The work of the geoscientist is similar to that of a detective who has to reconstruct the sequence of events from circumstantial evidence. The book draws on the specialisms and experience of the authors who are experts on the glacial history of the Earth.

Readership: Undergraduate and postgraduate students studying the Quaternary, researchers, and anyone interested in climate change, environmental change and geology. The book provides a rich collection of illustrations and photographs to help the readers at all levels visualise the dramatic consequences of glacier expansions during the Ice Age.

Central part of Gorner Glacier, Switzerland. Source: Agassiz (1841).

Chapter 1
Introduction

The Ice Ages! It is difficult, now, to understand the perplexity and bafflement and sheer disbelief that greeted this idea, over a century and a half ago: the idea of vast walls of ice invading from the north to engulf entire landscapes. This seemed like science fiction, a Gothic fantasy on a par with a belief in dragons and fairies and industrious aliens that built canals on Mars.

Zalasiewicz (2009, p. 68)

The meeting of the Swiss Society of Natural Science on 24 July 1837 in Neuchâtel began with a scandal. The young president of the Association, Louis Agassiz, spoke not about the latest results of his studies on fossil fishes as expected, which had made him famous. Instead, he decided to talk about the erratic blocks in the Jura Mountains (and in the vicinity of Neuchâtel) which he said were the legacy of a major glaciation. This ‘Discourse of Neuchâtel’ is considered the birth of the Ice Age Theory.

Agassiz was not the first person to have said this, but he was the first high-ranking scientist. His speech met with icy disapproval. On the subsequent field trip on 26 July, during which the participants could actually examine the evidence with their own eyes, Agassiz did not succeed in convincing the other experts. The glacial theory appeared to be a non-starter (Imbrie & Imbrie 1979).

1.1 In the Beginning was the Great Flood

People always tend to explain incomprehensible natural phenomena by processes they know. The notion of an ‘Ice Age’ was alien to the scientists of earlier centuries. They did know however that, in the course of the Earth’s history, back and again extensive areas of land had been inundated by the sea. It therefore seemed to make sense to interpret the legacy of the Quaternary, especially the erratic blocks, as the results of a great flood. Did not the Bible report a devastating deluge? In many parts of the Earth there were traces of that flood to be found. Johann Friedrich Wilhelm Jerusalem listed some of them. He wrote:

The greatest attention deserve the southward pointed shape of Africa and India, and all the great embayments all around Asia, from the Red Sea up to Kamchatka, all open to the south, which are the surest proof that the Earth once suffered a violent flood from the south, which is also confirmed by the large amount of skeletons of large land animals found in Siberia which are derived from a more southern country.

Jerusalem (1774)

When Jerusalem published these lines, belief in the literal meaning of biblical texts had ceased. Jerusalem, adviser to Duke Karl I of Brunswick-Wolfenbüttel, was one of the most important theologians of the German Enlightenment. He was an educated man who had spent years in Holland and England. In his interpretation of the flood, he includes the dead mammoths from Siberia. He was well aware that ‘petrified sea animals spread over the whole earth, such as the horns of Ammon’ could not be related to the biblical flood, but a flood – a very, very big flood – still seemed possible.

That the latter might have been the biblical deluge was only believed by a few at the beginning of the 19th century. One of them, the Reverend William Buckland of Oxford, introduced the term ‘Diluvium’ to the stratigraphic nomenclature in 1823.

While his contemporary Cuvier was convinced that the traces of the deluge were limited to the lowlands and valleys of the Earth, Buckland wrote:

The blocks of granite, which have been transported from the heights of Mont Blanc to the Jura mountains, could not have been moved from their parent mountain, which is the highest in Europe, had not that mountain been below the level of the water by which they were so transported.

Buckland (1823, p. 221)

Cuvier also wrote:

In certain countries, we find a number of large blocks of primitive substances scattered over the surface of secondary formations, and separated by deep valleys or even by arms of the sea, from the peaks or ridges from which they must have been derived. We must necessarily conclude, therefore, either that these blocks have been ejected by eruptions, or that the valleys (which must have stopped their course) did not exist at the time of their being transported; or, lastly, that the motions of the waters by which they were transported, exceeded in violence anything we can imagine at the present day.

Cuvier (1827, p. 23)

This early attempt at a natural explanation for the occurrence of boulders far from their source rocks corresponds to the rolling stone or mud flood theory, mainly advocated by Leopold von Buch (1815), but also by Alexander von Humboldt (1845) and the Swedish physician and scientist Nils Gabriel Sefström (1836). They assumed that the erratics had been transported by huge masses of water, the so-called ‘petridelaunic flood’. The reason why such masses of water would have been released and flooded out of the Alps and the mountains of Scandinavia remained open.

In England, Charles Lyell had argued in his Principles of Geology (1830–33) against the geological significance of disasters. Von Hoff was the first German scientist to turn against Cuvier’s catastrophism (1834). Neptunists quarrelled with Plutonists, and eventually the concept of a smooth transformation of the Earth seemed to prevail.

A new interpretation of the erratic blocks was found at the beginning of the 19th century. In a shallow, cold sea icebergs might have transported the boulders. The supporters of the drift theory (Box 1.1), including Darwin and the physicist Helmholtz, were not completely opposed to a larger extension of the former glaciers, but rejected large-scale glaciation. Even when Lyell (1840) discussed the origin of erratic boulders in northern Europe, he was strongly opposed to the neo-catastrophism envisaged by Agassiz.

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BOX 1.1 DRIFT-ICE TRANSPORT

The sandstone block in Figure 1.1 is 185 × 175 × 135 cm in size and its weight is estimated at 8 tons. It was found on a salt marsh covered with Spartina alterniflora. When the stone was pushed landward by drift ice, it left behind a distinct furrow in the ground (foreground right).

Figure 1.1 A block of sandstone on the lower saltmarsh at Isle-Verte, St Lawrence Estuary, Canada. Photograph by Jean-Claude Dionne.

Goethe had also heard that drift ice should have transported rock material from Sweden across the Øresund to Denmark. Was this the method by which the boulders in northern Germany had arrived in their present position?

There is no doubt that drift ice can move large stones. The coastal waters of northern Canada are covered with ice in winter. In the spring the ice cover breaks up, resulting in an ice drift along the coast. In its course, frozen rock and soil material are moved and redeposited. The Canadian geographer Jean-Claude Dionne has studied this phenomenon in numerou...

Table of contents

• Cover
• Title page
• Copyright
• About the Authors
• Preface
• Acknowledgements
• About the Companion Website
• Chapter 1 Introduction
• Chapter 2 The Course of the Ice Age
• Chapter 3 Ice and Water
• Chapter 4 Till and Moraines: The Traces of Glaciers
• Chapter 5 Meltwater: From Moulins to the Urstromtal
• Chapter 6 Maps: Where Are We?
• Chapter 7 Extent of the Glaciers
• Chapter 8 Ice in the Ground: The Periglacial Areas
• Chapter 9 Hippos in the Thames: The Warm Stages
• Chapter 10 The Course of Deglaciation
• Chapter 11 Wind, Sand and Stones: Aeolian Processes
• Chapter 12 What Happened to the Rivers?
• Chapter 13 North and Baltic Seas during the Ice Age
• Chapter 14 Climate Models and Reconstructions
• Chapter 15 Human Interference
• References
• Index
• EULA