Landscape Development

Transcription

1 CHAPTER 22 Landscape Development Chapter Summary Landscapes are described in terms of their topography: elevation, the altitude of the surface of the Earth above sea level; relief, the difference between the highest and the lowest spots in a region; and the varied landforms produced by erosion and sedimentation by rivers, glaciers, mass wasting, and wind. Elevation is a balance between tectonic activity and erosion rate. Tectonics (uplift and subsidence), erosion, climate, and the type of bedrock control the evolution of landscapes. Water, wind, and ice act to erode and transport rock material from the high spots and deposit it in the low spots. Over time, relief is subdued by both erosion and sedimentation. Landscapes go through different phases depending on tectonic activity and climate. For example, a landscape with high relief will form if tectonic activity is high, which in turn stimulates erosion. Erosion will at first enhance relief, but over time water, wind and ice will wear down the high spots and fill in the low spots with sediment. Current views of landscape evolution emphasize the competition between erosion and tectonic uplift. If uplift is faster, the mountain will rise; if erosion is faster, the mountains will be lowered. When tectonics dominates, mountains are high and steep, and they remain so as long as the balance is in favor of tectonics. When erosion exceeds uplift, slopes become lower and more rounded. Mountain building processes dominate convergent plate boundaries. Various feedback mechanisms may influence evolution of a mountain system at a convergent boundary. As the mountains become higher, glaciers can form. Ice is a very effective agent of erosion. Therefore, negative feedback develops whereas mountains get higher, glaciers become bigger and more numerous, and the faster the ice can erode. Over the long term (tens to hundreds of millions of years) this feedback mechanism probably speeds up the wearing down of high mountains. However, over the short term (thousands to millions of years) erosion may promote uplift and actually result in the highest peaks rising even higher, due to isostatic adjustments associated with erosional unloading. Learning Objectives In this section we provide a sampling of possible objectives for this chapter. No class could or should try to accomplish all of these objectives. Choose objectives based on your analysis of your class. Refer to Chapter 1: Learning Objectives How to Define Your Goals for Your Course in the Instructional Design section of this manual for thoughts and ideas about how to go about such an analysis. 216

2 Landscape Development 217 Knowledge Know how landscapes are described in terms of their topography: elevation, the altitude of the surface of the Earth above sea level, and relief (the difference between the highest and the lowest spots in a region). Understand how the great variety of landscapes result from sculpturing geologic processes such as erosion and sedimentation by rivers, glaciers, mass wasting, and wind. Understand how landscapes go through different phases depending on tectonic activity and climate. Know the major landform provinces for North America. Know characteristic landforms associated with active tectonic plate boundaries. Understand how Earth systems and plate tectonics control landscapes. Understand the relationship between tectonics and erosion. Skills/Applications/Attitudes Chapter 22 provides an opportunity for application of the material in previous chapters. Another way of saying this is that students, by taking this geology course, have acquired a new set of eyes through which to view the world. It is a good time to test those new eyes with exercises requiring application and synthesis. Given facts about a region s elevation, relief, and climate make predictions about the landforms one would expect to find there. Given a particular topography (mesa, cuesta, hogback, valley and ridge topography) sketch and describe its features. Hint: The following figures could be downloaded from the instructor s Web site: aretes (see Figure 22.6), mesas (see Figure 22.8), valley and ridge topography (see Figures and 22.13), cuestas (see Figure 22.14), hogbacks (see Figure 22.15). General Education Skills Write a review of an article out of Scientific American or a professional journal. (writing/critical thinking) Freshman Survival Skills Exam Preparation As the end of the semester approaches students will appreciate helpful ideas about preparing for finals and taking exams. Focused Review This chapter depends heavily on concepts students have been learning throughout the semester. A focused review of previous material will be more beneficial than usual. Hint: The section Vital Information at the beginning of Chapter 22 of the Student Study Guide for Understanding Earth outlines much of the key material you might choose to review. Consider combining review during lecture with a structured assignment requiring students to do their own review work.

3 218 PART II CHAPTER 22 Sample Lecture Outline Sample lecture outlines highlight the important topics and concepts covered in the text. We suggest that you customize it to your own lecture before handing it out to students. At the end of each chapter outline consider adding a selection of review questions that represent a range of thinking levels. Chapter 22: Landscapes Tectonic and Climate Interaction Topography, Elevation, and Relief Contour lines Topographic maps Landforms Types Plateaus Mountains and hills Badlands Mesas Hogbacks Cuestas River and tectonic valleys Streams and bedrock erosion Stream power dynamic balance between slope, discharge, and sediment load Abrasion Tectonics vs. Erosion Feedbacks Uplift vs. erosion Climate vs. topography Climate Latitude Models for Landscape Evolution Davis cycle of erosion Hack dynamic equilibrium Penck uplift competes with erosion

4 Landscape Development 219 Teaching Tips Cooperative/Collaborative Exercises and In-Class Activities Refer to Chapter 4: Cooperative Learning Teaching Strategies in the Instructional Design section of this manual for general ideas about conducting cooperative learning exercises in your classroom. Coop Exercise: Landscapes Tectonic and Climate Interaction Flowchart The following exercise from the Student Study Guide makes a good in-class exercise. Display the flowchart below as a slide or overhead, then have students pair-up with a neighbor to fill in the blanks. Instructions: Place the following words in the correct positions on the flowchart: tectonic activity high relief low relief erosion physical weathering chemical weathering uplift stimulates e.g., convergent boundary High relief, cold and dry, polar or desert activation of a plate boundary weathering dominates Low relief, hot and dry, tropical weathering dominates General Education Skills The Geology in Practice exercises offer an opportunity for students to think about feedback relationships between uplift, erosion and isostatic adjustments. The article entitled A Review of How Erosion Builds Mountains by Nicholas Pinter and Mark T. Brandon, Scientific American, April 1997, pp , provides a basis for this investigation. Below is a brief summary of this article. Major Themes Discussed in How Erosion Builds Mountains:

5 220 PART II CHAPTER 22 Mountains are a product of plate tectonics, erosion and climate. Plate tectonics determines the location of mountain on Earth and plate tectonic processes produce the thick crustal root that helps to support many mountain ranges. Erosion and climate are closely linked and act together to determine how fast rock is removed off the mountain. Erosion coupled with isostatic compensation can result in a positive feedback, whereas rock is removed from a mountain range by erosion, the buoyant response of the crustal root results in additional uplift. Additional Themes: Orographic effects can help to determine the ultimate shape of mountains. The history of a mountain range can be characterized in three basic stages: 1. Tectonics act to thicken crust and induce uplift at rates greater than erosion. 2. Rate of uplift and erosion are about equal, so the highest areas within the mountain range can get even higher. 3. Erosion surpasses uplift and the mountain range wears down. There is continued debate about the relationship between mountain building and global climate. Freshman Survival Skills Focused Review This chapter depends heavily on concepts students have been learning throughout the semester. A focused review of previous material will be even more beneficial than usual. Hint: The section Vital Information at the beginning of Chapter 22 in the Student Guide for Understanding Earth outlines much of the key material you might choose to review. Consider combining review during lecture with a structured assignment requiring students to do their own review work. The Study Guide is available in the Understanding Earth e-book. Exam Preparation As the end of the semester approaches students will appreciate helpful ideas about preparing for finals and taking exams. Hint: You will find lots of test taking and exam preparation tips in the Student Study Guide and in the teaching tips section of many chapters in this manual. Appendix A is a study plan for preparing for exams, and Appendix B offers helpful ideas about preparing for final exam week. Show slides with exam preparation tips as background during your lecture. Provide students a thorough exam review session close to the time of the final. Show slides with test taking tips during your exam review section. Finally, if you have a class Web site consider posting some materials or links that will help students prepare for exams. Topics for Class Discussion Introduce the concept of isostatic adjustment due to loading, e.g., accumulation of ice, and unloading, e.g., the retreat of the ice sheets, erosion of high mountains.

6 Teaching Resources Student Study Guide Highlights In Part I, chapters provide strategies for learning geology. Ideally, students would read these chapters early in the course. Chapter 1: Brief Preview of the Student Study Guide for Understanding Earth Chapter 2: Meet the Authors Chapter 3: How to Be Successful in Geology In Part II, Chapter 22: Landscapes Tectonic and Climate Interaction Before Lecture: Preview Questions and Brief Answers Vital Information from Other Chapters During Lecture After Lecture: Check Your Notes: Have You Study Tip: Learn by Drawing Intensive Study Session Study Tip for Figure and Earth Issues 22.1 Exam Prep: Chapter Summary Practice Exercises: Landscapes: Tectonic and Climate Interaction Flowchart Comparison of Some Landforms Review questions Test Taking Tip: Think Logically (part of the Understanding Earth e-book) Landscape Development 221