Lesson 5: Volcanoes and Earthquakes
This is the last of the three lessons drawn from Chapter 2 that introduce background information we'll use to understand a wide range of topics later in the semester. Our focus this week is on volcanic and sesimic activity—how these processes operate, how their effects can be recognized, and how they shape the features that define so many national park landscapes.
As you read through pages 34-45 of Chapter 2 it will be helpful to take notes so that you can keep track of major points and have the information readily available when these topics arise in discussions later in the semester. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.
Weekly Learning Objectives
Upon successful completion of this week's lesson, a student is expected to be able to:
- Infer likely mechanism (decompression melting or hydration melting) that forms magmas in a given tectonic setting.
- Recognize the four common types of volcanoes (shield volcanoes, composite volcanoes, cinder cones, and domes) from photographs or cross-sectional drawings, and explain how the shape and typical eruptive style (lava flows, explosive eruptions, or both) of each is related to the viscosity of the lavas it produces.
- Describe how you could distinguish among ash fall, pyroclastic flow, and debris flow activity at a volcano if you were to witness its eruption, and indicate which of these processess are likely to pose serious threats to people living in valleys near the volcano.
- Suggest why the longer the interval between earthquakes along a fault the greater their magnitudes are likely to be according to the elastic rebound model.
- Distinguish between an earthquake's magnitude and its intensity, and explain how differences in the distance to a site and the type of surface material there are likely to affect an earthquake's intensity.
- Estimate how the amplitudes of ground motion at a given distance from the epicenter and the total amounts of energy released differ for two earthquakes with different magnitudes.
- Predict which of the seismic waves generated by an earthquake—P, S, or surface waves—are likely to arrive first at a distant seismic station and which are likely to arrive last. (You'll use this information in Exercise 5.)
Reading and Browsing Assignment
- Read pages 34-45 in Chapter 2, focusing on the topics outlined in the learning objectives above.
- Browse through the How Volcanoes Work site authored by Vic Camp at San Diego State University. The site has sections on topics ranging from eruption dynamics to volcanic landforms that supplement our text, and each section includes a brief "self-test" that you can try.
- Learn about the eruptive history and likely future hazards posed by Mount Shasta, which was once proposed as the centerpiece of a National Park, by browsing through the geology section of the Mount Shasta Companion.
- Browse through the Southern California Earthquake Center's education site Investigating Earthquakes through Regional Seismicity. You'll find lots of in-depth information here, as well as some interestng activities that you can try.
- California is one of the most seismically active places in the world. You can see a near-real time map of the the past week's earthquake activity in the state by visiting the Recent Earthquakes Map. (Click on a quake and see what happens!) Also, check out the California Earthquake Forecast map based on recent aftershock activity.
Exercise 5 (Due by 9:00 AM on Monday, 15-Feb-2010)
After you have read the last part of the chapter and are comfortable with the concepts outlined in the learning objectives above, point your browser to Virtual Courseware's Earthquake exercise. Under "Main Activities" on the first screen, click "Travel Time" and work through the exercise by following the instructions and using each tool in sequence to construct a travel time diagram. Like the earlier radiometric dating exercise you worked on this one uses Java applets that may take a little while to load; be patient. At the end of the first part of the exercise return to the main screen (you do not need to save your results from the first part.)
Next, work through the "Epicenter and Magnitude" exercise (third button under "Main Activities".) At the end of this part of the exercise you will be asked if you want to take a quiz. Click yes, fill in your name, and enter 1513648 as your class code. (Write this number down now so that you have it when you go to the Earthquake site.) Complete the 10-question quiz. When you are done you will be able to review your score, and the program will automatically post a copy of it to a grade book that I will access next Monday (15-Feb-2010). When you've finished both parts of the exercise and taken the associated quiz, you'll be finished with Exercise 5. Have fun—this is a very cool way to learn about how seismologists determine the locations and magnitudes of earthquakes.
Quiz 5 (Due by 9:00 AM on Monday, 15-Feb-2010)
After you feel you have met the learning outcomes outlined above, please complete Quiz 5 in the Etudes "Assignments, Tasks, and Tests" tool. There are ten questions, each worth one point. If you can answer all of them correctly it means that you know your way around volcanoes and earthquakes pretty well and are ready to move on to learn about parklands shaped by continental rifting next week.
