Los Angeles against the Mountains

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Assignments	John McPhee, The Control of Nature, Part 3
Reminders

Reading Discussion Questions

Read the entire section. Then go back and review by focusing your attention on the following questions for discussion. (Page numbers in parentheses are approximate; most questions are discussed in many places throughout the reading.)

1. What happened to the Genofiles?

    

2. What is a "debris flow"? (185)

    

3. How frequent are they? (202)

    

4. What happened to Amos Lewis in the Middle Fork debris flow? (219-221)

    

5. How are debris flows controlled?
   1.  
   2. Do these measures work? (269)

       

   3. Where do they put the material they clean up after a debris flow? (271)

    

6. What is an "alluvial fan"? What are the hazards of living on one? (234)

    

7. "Why does anybody live there?" (229, 246, 252ff)

What causes a debris flow?

1. Rapid mountain building
   1. The San Gabriel mountains are rising faster than they are falling down. True or False? (204)
   2. From base to summit, the San Gabriels are taller than the Rockies. True or False? (205)
   3. What is the slope of some of the San Gabriel mountainsides?
   4. Angle of repose (207)
   5. Colliding tectonic plates (226)

    

2. Earthquakes
   1. Shattering of rock (225)
   2. What is "incompetent" rock?

    

3. Chaparral fires
   1. Why are fires a necessary prerequisite for debris flows in this area?
   2. The hotter the fire the greater the debris flow. True or False?
   3. Describe the formation of waterproof soil. (207 ff)
   4. What are rills? (211 ff)

    

4. Concentrated intense rainfall
   1. How does the ordinary average rainfall of Los Angeles compare to a desert? (214)
   2. How do thunderstorms and intense rain mobilize debris flows? (202)
   3. Might debris flows be more severe in an El Nino year? Explain.