The Earth′s Land Surface

Landforms and Processes in Geomorphology

Kenneth J Gregory

• Publisher: SAGE Publications Ltd
• Year: 2010
• Print ISBN: 9781848606203, 9781848606197
• eBook ISBN: 9781446245576
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

"Given the sheer scale of the topic under consideration here, Professor Gregory does well to condense it into bite-size pieces for the reader. I recommend this text to all undergraduate students of physical geography and earth sciences, particularly to those in their first and second years... This book is a comprehensive and (crucially) inexpensive text that will provide students with a useful source on geomorphology."
- Lynda York, The Geographical Journal

"I would highly recommend this to anyone doing geology or geography at university as a ?go to? book for geomorphology and landform."
- Sara Falcone, Teaching Earth Science

"An excellent source of information for anyone who needs a well-informed, easy to use reference volume to introduce them to the fascinating complexities of the earth's land surface, past, present and future."
- Angela Gurnell, Queen Mary, University of London

This introductory text details the land surface of the earth in a readable style covering the major issues, key themes and sensitivities of the environments/landscape.

Emphasising the major ideas and their development, each chapter includes case studies and details of influential scientists (not necessarily geomorphologists) who have contributed to the progress of understanding. Providing a very clear explanation of the understanding achieved and of the debates that have arisen, the book is comprised of 12 chapters in four sections:

• Visualising the land surface explains and explores the composition of the land surface and outlines how it has been studied.
• Dynamics of the land surface considers the dynamics affecting the earth?s land surface including its influences, processes and the changes that have occurred.
• Environments of the land surface looks to understand the land surface in major world regions highlighting differences between the areas.
• Management of the land surface is an examination of the current and future prospects of the management of the earth?s land surface.

With pedagogical features including further reading, questions for discussion and a glossary, this original, lively text is authored by one of the leading experts in the field and will be core reading for first and second year undergraduates on all physical geography courses.

PART I

VISUALIZING THE LAND SURFACE

1

RECOGNIZING THE LAND SURFACE

Terra firma, a Latin phrase for solid earth, is used to differentiate land from sea – thus connoting the land surface of the Earth. It is used specifically in the Amazon floral region where vegetation above flood level is called terra firma and that below, igapo or varzea. Terra firma in a search engine produces more than 11 million results, referring to tiles, travel firms, landscapes, rug company and many others but only one book (Orban, 2006). It is surprising that the land surface of the Earth has not received more explicit attention – perhaps because with hindsight it seems to have been hijacked by disciplines whose prime purpose lies elsewhere: a reason for what Tooth (2009) has described as invisible geomorphology where geomorphological awareness still needs to be raised by stressing the discipline’s relevance and contribution to a host of environmental issues. For over a century, museums have been one way to inform about the surface of the Earth, but they emphasized geology, natural history and archaeology. In recent decades public awareness of the surface of the Earth has increased through press and media news reports and documentaries, cinema and the internet. It is ironic that the land surface of the Earth has not received more explicit attention but thought of geologically in terms of rock and tectonic control; biologically in terms of the vegetation types and ecosystems spread across the surface; economically and archaeologically in terms of the environments provided. This chapter introduces terra firma, what it is, how we think of it, and how we have divided it up.

1.1 WHAT IS THE LAND SURFACE?

Over the last five decades data collected by remote sensing from orbital satellites has revolutionized our valuation of the land surface of the blue planet, by enabling definitive measures of its characteristics. Complementary recent progress has been provided by computer analysis and Geographical Information Systems (GIS), by satellite navigation, and by advances in dating techniques. It is salutary to recall that the shapes of the continents were not known until the eighteenth and nineteenth centuries when national topographic surveys were undertaken. Although we should now expect little variance in dimensions of the land surface (see Table 1.1), it is surprising how much variation occurs in published estimates – some because of conversions to the International System of Units (SI), or because they have not been verified or definitions have varied, but some because changes of the land surface have occurred.

Table 1.1 DIMENSIONS FOR THE LAND SURFACE

Figure 1.1 Comparative hypsometries (elevation is plotted against percentage of the Earth’s surface area; based on http://comp.uark.edu/-sboss).

A way of demonstrating the overall distribution of the land surface is according to elevation above sea level. Such a hypsometric or hypsographic curve is a graph showing the proportion of the land mass occurring above a given level; it can be constructed for Earth as a whole or a part such as a drainage basin or glacier. Unlike the hypsometric curve for the moon or Venus that for the Earth (see Figure 1.1) is bimodal with one peak for the continents and one for the ocean basins, revealing more of the Earth’s surface beneath the sea than above it.

Ice covers more than 10% of the land surface and frequent references to rates of melting of glaciers and ice sheets reflect the changes taking place so that regular auditing and monitoring of glacier and ice cap extent is necessary (see Table 1.2). Whereas ice-covered areas dominantly occur in high latitudes and high mountains, fresh water bodies are distributed over approximately 1% of the land surface in all continents. The largest closed basin lake is the Caspian Sea with a coastline approximately 7000 km long and a drainage basin covering 3.1 million km². Lake Baikal is the deepest single body of water with a volume of 22,000 km³ – nearly equivalent to the total volume in all five Great Lakes of North America. Some countries are particularly proud of their lakes. Finland, known as the Land of the Thousand Lakes, actually has more than 180,000. Manitoba claimed 100,000 lakes to beat Minnesota, which proclaimed ‘Land of 10,000 Lakes’ on its license plates. Lake Huron, the second largest lake in the world according to its surface area of 117,702 km², is one of the five Great Lakes of North America which are part of a system collectively containing some 22% of the world’s freshwater – enough to cover the 48 contiguous states of the USA to a depth of 2.9 m, with a surface area nearly the same as that of the United Kingdom.

When seen from space, the surface of the blue planet, in addition to land, water and ice, shows the green of forest, and broad categories of land use (see Table 1.1). As much of the land surface has been substantially affected by human action, dramatically increased since the nineteenth century, a new geological period, the Anthropocene, was suggested in 2000 by Paul Crutzen, a Nobel prize winner, because he regarded human impact on the Earth as so significant that it justified a new geological era to succeed the Pleistocene and Holocene of the Quaternary in the geological time scale (see Figure 5.1). A 2008 article (Zalasiewicz et al., 2008) was aptly entitled ‘Are we now living in the Anthropocene?’.

Table 1.2 GLACIER INVENTORY: EXAMPLES OF PROGRESS

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1. Plans for an inventory of global glacier features were included in the International Hydrological Decade (1965–1974), with the intention of repeating the survey every 50 years to detect changes in glaciers. By 2008 about 37% of the estimated total glacier surface had been inventoried, available through the World Glacier Monitoring Service (WGMS) in Zürich and National Snow and Ice Data Center (NSIDC) in Boulder.
2. A simplified inventory method was developed in the early 1980s mainly based on satellite images, as outlined in Global Land Ice Measurements from Space (GLIMS) which covers 34% of the estimated glacier surface outside Greenland and Antarctica. See http://www.glims.org/ (accessed 17 March 2009).

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The Earth’s land surface is not static because change is, and always has been, a characteristic feature. Each year sees changes in detail – in ice extent for example. In addition to seasonal changes there are also changes from year to year, as drought years follow wetter years, and there are also evolutionary changes, for example as some coastlines progressively advance, complemented by others which are submerged. Some of the most dramatic changes arise from human impact, and most recently from global change on a scale which is substantial and potentially very serious. The level of the Caspian Sea fell over the last century so that, between 1927 and 1977, many economic activities, including oil exploration, oil field development, and pipeline construction, developed on the exposed lake floor. The lake level reached a record low of 29.0 m below mean sea level (Rodionov, 1990) in 1977, prompting an engineering solution response to bring water to the Sea from wetter parts of the Soviet Union (Glantz, 1995). After 1977 therefore the level of the Caspian began to rise rapidly (Rodionov, 1990) with consequential environmental problems including coastal inundation because of sea level rise; water pollution by raw sewage and oil production; fishing pressure and its impacts on fish populations (Glantz, 1995). The fall in level of the Aral Sea has also been dramatically affected by human activity: by 1989 the sea level had fallen by 14.3 m and the surface area had shrunk from 68,000 km² to 37,000 km². In the twenty-first century, as a result of conservation measures, the Sea level is rising again.

Interpreting the land surface requires a range of time scales analogous to the different resolutions of a microscope. A perceptive way of envisaging time scales (Schumm and Lichty, 1965) distinguished steady, graded and cyclic time (see Table 1.3). Any point on the land surface of the Earth can be thought of as a location in space and time so that to understand its characteristics we have to refer to changes occurring over time: some of the actual surface characteristics are the result of relatively recent changes, some parts of the Earth retain characteristics developed over millions of years (see Quaternary chronology, Glossary p. 306). Where human impact is substantial then the surface characteristics may be just years or decades old. Time scales are inextricably combined with spatial scales so that one of the greatest challenges in studying the land surface of the Earth is to apply results gained from study at one time and spatial scale to one of the other time scales. Relating process measurements made over years or decades to development over centuries or millennia requires reconciling timeless and timebound scales.

Table 1.3 SOME CLASSIFICATIONS OF TIME

1.2 ENVISAGING THE LAND SURFACE

How do we describe the land surface of the Earth? Language descriptions of characteristics of the surface are the obvious way, applying words to particular earth surface features. In English the nouns mountains, plains, valleys, plateaus have equivalents in other languages. Inevitably some languages include words for Earth surface characteristics according to the environment in their particular country, so that a language of place (Mead, 1953) reflects the fact that some vocabularies have words for particular features which do not have direct counterparts in other languages. In Russian there are words for types of valley, like balki, which cannot easily be translated into English because no comparable features occur as extensively in England or in America. Many descriptive words have now evolved to describe landforms – landform refers to the morphology and character of the land surface resulting from the interaction of physical processes with the surface materials in the land surface environment. Words for particular types or shapes of feature have become adopted as scientific terms so that words such as corrie or the Welsh word cwm for armchair-shaped hollows, became accepted as features of glacially eroded landscapes. Words gradually became adopted in this way so that it is not easy to discern when landform first became basic for the science of geomorphology (see p. 19, Chapter 2).

Scientists in the nineteenth century included Baron Ferdinand von Richthofen (1833–1905), who had trained in geology and geography at Breslau (now Wroclaw) and published a book, arising from his travels, on regional geology and geography in 1886 which may be the first systematic textbook of modern geomorphology (Fairbridge, 1999). Ways in which landforms gradually became assimilated into the scientific literature of studies of the land surface of the Earth are illustrated in Table 1.4, showing the importance of exploration of the American West and the contributions of William Morris Davis which may have formalized the recognition of the importance of landform (Davis, 1900: 158). Characteristics of the land surface of the Earth and its processes are not only reflected in language but also perceived through cultures, in art and music.

Table 1.4 ILLUSTRATIONS OF THE EMERGENCE OF LANDFORMS AS THE SCIENTIFIC BASIS FOR STUDY (SEE ALSO CHORLEY ET AL., 1964)

A second way of considering the surface of the Earth involves its contribution to environment or to nature. Einstein is reputed to have described environment as ‘everything that isn’t me’ but usually it is thought of as the set of characteristics or conditions surrounding an individual human being, an organism, a group of organisms or a community. Of the several types of defined environment, the natural environment is a theoretical concept, which includes all living and non-living things occurring naturally on Earth, whereas the physical environment or biophysical environment refers to phenomena excluding humans. Nature comprises the essential qualities of environment: it can be seen as a group of interrelated objects that objectively exist in the world independent from humans, together with the biophysical processes that create and maintain the objects; or as a concept that is socially c...

Table of contents

• Cover Page
• Title
• Copyright
• Contents
• Preface
• Acknowledgements
• PART I VISUALIZING THE LAND SURFACE
• PART II DYNAMICS OF THE LAND SURFACE
• PART III LANDFORM EVOLUTION
• PART IV ENVIRONMENTS OF THE LAND SURFACE
• PART V MANAGEMENT OF THE LAND SURFACE – FUTURE PROSPECTS
• Glossary of key advances
• Colour Plates
• References
• Index