Before delving into the mathematical intricacies with which much of this book is concerned, one might well ask why we are pursuing this topic - glacier mechanics? For many who would like to understand how glaciers move, how they sculpt the landscape, how they respond to climatic change, mathematics does not come easily. I assure you that all of us have to think carefully about the meaning of the expressions that seem so simple to write out but so difficult to understand. Only then do they become part of our vocabulary, and only then can we make use of the added precision which mathematical analysis, properly formulated, is able to bring. Is it worth the effort? That depends upon your objectives; on why you chose to study glaciers.
There are many reasons, of course. Some are personal, some academic, and some socially significant. To me, the personal reasons are among the most important: glaciers occur in spectacular areas, often remote, that have not been scarred by human activities. Through glaciology, I have had the opportunity to live in these areas; to drift silently in a kayak on an ice-dammed lake in front of our camp as sunset gradually merges with sunrise on an August evening; to marvel at the northern lights while out on a short ski tour before bedtime on a December night; and to reflect on the meaning of life and of our place in nature. Maybe some of you will share these needs, and will choose to study glaciers for this reason. I have found that many glaciologists do share them, and this leads to a comradeship which is rewarding in itself.
Academic reasons for studying glaciers are perhaps difficult to separate from socially significant ones. However, in three academic disciplines, the application of glaciology to immediate social problems is at least one step removed from the initial research. The first of these is glacial geology. Glaciers once covered 30% of the land area of the Earth, and left deposits of diverse shape and composition. How were these deposits formed, and what can they tell us about the glaciers that made them? The second discipline is structural geology; glacier ice is a metamorphic rock that can be observed in the process of deformation at temperatures close to the melting point. From the study of this deformation, both in the laboratory and in the field, much can be learned about the origin of metamorphic structures in other crystalline rocks that were deformed deep within the Earth. The final discipline is paleoclimatology. Glaciers record climatic fluctuations in two ways: the deposits left during successive advances and retreats provide a coarse record of climatic change which, with careful study, a little luck, and a good deal of skill, can be placed in correct chronological order and dated. A more detailed record is contained in ice cores from polar glaciers such as the Antarctic and Greenland ice sheets. Isotopic and chemical variations in these cores reflect present atmospheric circulation patterns and past changes in the temperature and composition of the atmosphere. Changes during the past several centuries to several millennia can be rather precisely dated by using core stratigraphy. Changes further back in time are dated with less certainty using flow models.
Relatively recent changes in climate and in concentrations of certain anthropogenic substances in the atmosphere are attracting increasing attention as humans struggle with problems of maintaining a healthy living environment in the face of overpopulation and the resulting demands on natural resources. Studies of ice cores and other dated ice samples provide a baseline from which to measure these anthropogenic changes. For example, levels of lead in the Greenland ice sheet increased about four-fold when Greeks and Romans began extracting silver from lead sulphides (Hong et al., 1994). Then, after dropping slightly in the first millennium AD, they increased to ~80 times natural levels during the industrial revolution and to ~200 times natural levels when lead additives became common in gasoline (Murozumi etal., 1969). These studies are largely responsible for the fact that lead is no longer used in gasoline. Similarly, measurements of CO2 and CH4 in ice cores have documented levels of these greenhouse gases in pre-industrial times.
Other applications of glaciology are not hard to find. An increasing number of people in northern and mountainous lands live so close to glaciers that their lives would be severely altered by ice advances comparable in magnitude to the retreats that have taken place during the past century in many parts of the world. Tales of glacier advances gobbling up farms and farm buildings and of ice falls smashing barns and houses are common from the seventeenth and eighteenth centuries, a period of ice advance as the world entered the Little Ice Age. Records tell of buildings being crushed into small pieces and mixed with "soil, grit, and great rocks" (Grove, 1988, p. 72). The Mer de Glace in France presented a particular problem during this time period, and several times during the seventeenth century exorcists were sent out to deal with the "spirits" responsible for its advance. They appeared to have been successful, as the glaciers there were then near their Little Ice Age maxima and beginning to retreat.
Other people live in proximity to streams draining lakes dammed by glaciers. Some of the biggest floods known from the geologic record resulted from failure of such ice dams, and smaller floods of the same origin have devastated communities in the Alps and Himalayas.
Somewhat further from human living environments, one finds glaciers astride economically valuable deposits, or discharging icebergs into the shipping lanes through which such deposits are moved. What complications would be encountered, for example, if mining engineers were to make an open pit mine through the edge of the Greenland Ice Sheet to tap an iron deposit? What is the possibility that the present rapid retreat of Columbia Glacier in Alaska will increase perhaps ten-fold, perhaps one hundred-fold, the flux of icebergs into shipping lanes leading to the port of Valdez, at the southern end of the trans-Alaska pipeline? Were shipping to be halted there for an extended period so that the oil flow through the pipeline had to be stopped, oil would congeal in the pipe, making what one glaciologist referred to as the world's longest candle.
Glacier ice itself is an economically valuable deposit; glaciers contain 60% of the world's fresh water, and peoples in arid lands have seriously studied the possibility of towing icebergs from Antarctica to serve as a source of water. People in mountainous countries use the water not only for drinking, but also as a source of hydroelectric power. By tunneling through the rock under a glacier and thence up to the ice-rock interface, they trap water at a higher elevation than would be possible otherwise, and thus increase the energy yield. Glaciologists provided advice on where to find streams beneath the glaciers.
With the threat of global warming hanging over the world, the large volume of water locked up in glaciers and ice sheets represents a potential hazard for human activities in coastal areas. Collapse of the West Antarctic Ice Sheet could lead to a worldwide rise in sea level of 7 m in, perhaps, less than a century. Were this to be followed by melting of the East Antarctic Ice Sheet, sea level could rise an additional 50 m or so. Concern over these prospects has stimulated a great deal of research in the past two decades.
Lastly, we should mention a proposal to dispose of radioactive waste by letting it melt its way to the base of the Antarctic Ice Sheet. How long would such waste remain isolated from the biologic environment? How would the heat released affect the flow of the ice sheet? Might it cause a surge, with thousands of cubic kilometers of ice dumped into the oceans over a period of a few decades? This would raise sea level several tens of meters, with, again, interesting consequences! To accommodate these concerns, later versions of the proposal called for suspending the waste canisters on wires anchored at the glacier surface. The whole project was later abandoned, however, but not on glaciological grounds. Rather, there seemed to be no risk-free way to transport the waste to the Antarctic.
A good quantitative understanding of the physics of glaciers is essential for rigorous treatment of a number of these problems of academic interest, as well as for accurate analysis of various engineering and environmental problems of concern to humans. The fundamental principles upon which this understanding is based are those of physics and, to a lesser extent, chemistry. Application of these principles to glacier dynamics is initially straightforward but, as with many problems, the better we seek to understand the behavior of glaciers the more involved, and in many respects the more interesting, the applications become.
So we have answered our first question; we study glaciers for the same reasons that we study many other features of the natural landscape, but also for a special reason which I will try to impart to you, wordlessly, if you will stand with me looking over a glacier covered with a thick blanket of fresh powder snow to distant peaks, bathed in alpine glow, breathless from a quick climb up a steep slope after a day of work, but with skis ready for the telemark run back to camp. "Maktig," my companion said - powerful.
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