Los Angeles Against the Mountains Assignment


GEOS 348- Environmental Geology

Assignment #2

Los Angeles Against the Mountains Assignment- Write a well written review of John

McPhee’s essay and be sure to answer the following questions within the body of the essay.

1a. What are debris flows and how are they generated?

1b. What happens to the debris after the basins have filled up?

2a. What are the primary natural factors that contribute to debris flow generation? [Consider the tectonic, climatic, and biological factors].

2b.What is chaparral , and what role does it play in the generation of debris flows in southern


2c. The Santa Ana winds are famous in LA. How do these winds contribute to debris flows?

2d . Dry ravel can be heard in the hills above L.A. What role does this play in the generation of debris flows?


Hydrophobic layers are common in soils in the San Gabriels. How are these formed and what role do they play in the destabilization of hill slopes?

2f. Plate tectonics is responsible for much of the relief of the San Gabriels. How has the geometry of the San Andreas affected uplift rates in the area?

3. What are the human factors?

4a. What engineering methods have been used to reduce hazards? What is their effectiveness and environmental cost?

4b. How are debris basins and crib structures utilized to reduce debris flow damage?

4c.How are deflection walls used in the San Gabriel Mountains?

5a. What do you think is the general state of people's knowledge of the debris-flow hazard in the

LA area?

5b. What do you think about the realtors' responses to questions about the debris flow hazards

5c. What do you think of the Angelenos' responses to questions about the debris flow hazard

6. What is the responsibility of LA County, the state of California, and USA citizens (taxpayers) as a whole in responding to debris-flow disasters?

7. How has the policy adopted by LA in their battle against the San Gabriels affected the health of nearby beaches?

8. Would you buy a house in the San Gabriel Mountains? Explain.

Remember when considering the natural and human factors be sure to discuss the sequence of events that precede debris flow events.