Chapter 11 Glaciers

Chapter 11 Glaciers - 2009 Allan Ludman and Stephen Marshak...

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1 CHAPTER 11 GLACIAL LANDSCAPES PURPOSE • To learn how glaciers erode and deposit material • To become familiar with landforms carved and deposited by glaciers • To learn to distinguish glaciated landscapes from those formed by other agents of erosion. MATERIALS NEEDED • Colored Pencils • Ruler and paper for constructing topographic profiles 11.1 INTRODUCTION Glaciers hold more than 21,000 times the amount of water in all streams – about 75% of Earth’s fresh water. Today, huge continental ice sheets cover most of one continent (Antarctica) and nearly all of Greenland. Smaller glaciers carve valleys on the slopes of high mountains causing a characteristically sharp, jagged topography (Figure 11.1). Distinctive landforms show that continental glaciers were even more widespread during the Pleistocene Epoch – the so-called “Ice Ages”, covering much of northern Europe and North America. Figure 11.1 Jagged topography typical of areas affected by alpine glaciers Grand Teton Mountains, Wyoming Today, glaciers are receding at rates unprecedented in human history. As they shrink, the balance of the water cycle changes among glaciers, oceans, streams, and groundwater, altering our water supply © 2009 Allan Ludman and Stephen Marshak W.W. Norton & Company
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2 and modifying ecologic systems worldwide. Glaciated landscapes contain clues to past climate changes and help us understand what is happening now and plan for the future. We know, for example, that continental glaciers advanced and retreated several times during the Pleistocene and how fast those changes were. This enables us to measure human impact on the rates of these processes. 11.1.1 Types of glaciers Some small glaciers form on mountains and flow downhill, carrying out their erosion and depositional work in the valleys they carve. These are called, appropriately, mountain, valley, or Alpine glaciers ( Figure 11.2a). Although they flow in valleys like streams, mountain glaciers work differently and form distinctly different landscapes. The Antarctic and Greenland continental ice sheets described earlier are not confined to valleys. They flow as masses of ice thousands of feet thick and flow as masses of ice across the countryside, dwarfing hills and burying all but the tallest peaks beneath their ice (Figure 11.2b). The North American and European ice sheets did the same during the Pleistocene. Exercise 11.1 compares the ways in which glaciers and water do their geologic work. Figure 11.2 Mountain and continental glaciers a. Crowfoot glacier, Banff National Park, Canada b. Continental ice sheet, Antarctica Exercise 11.1 Comparison of glaciers and streams Glaciers behave differently from stream water, even those that occupy valleys. Based on what you know about streams and have learned about glaciers, complete the following table.
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3 Streams Continental Glaciers Valley Glaciers State of matter Liquid Composition H 2 O Areal distribution In channels with tributaries flowing into larger streams
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Chapter 11 Glaciers - 2009 Allan Ludman and Stephen Marshak...

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