Lesson 15: California's Coast
Perhaps more than by any other feature, California is defined by its coastline. Although some parts of the state's coast remain much as they were when European settlers arrived during the early 19th century (Point Reyes headland, right) many others have been altered dramatically by the wetland modification and construction necessary to accomodate the growth of coastal populations. This chapter explores how several natural processes— from wave erosion and longshore transport to tectonic uplift and sea-level rise—continue to shape the state's coast. These processes also create potential hazards for coastal residents that are likely to impact almost everone in the state—whether you live in a coastal county or pay higher insurance and public safety costs to assist those who do—in the years to come. Finally, proposals to drill for oil and natural gas off the state's shore are currently being debated in an effort to balance economic and environmental concerns. Although we will not consider the pros and cons of these proposals directly, we will look at the geologic origins of such deposits next week when we explore the Transverse Ranges.
In chapter 15 Harden reviews coastal processes such as wave erosion and longshore transport and explores how California's active tectonics interact with these processes to produce both submergent and emergent coastlines as well as marine terraces. In this week's exercise you'll have a chance to assess the potential effects of a tsunami on a coastal town which, as recent events in Japan remind us, is a potential threat to any coastal area.
As you read about California's coast be sure to take careful notes on the topics covered by the learning objectives below. As during previous weeks, you'll find that writing out key facts in your own words or making neatly labeled drawings will help you better understand the significance of what you've read and spot any gaps in your knowledge. Don't hesitate to post any questions you have to the Discussion Board so that your classmates or I can help you figure them out. Having good notes will also make it easier for you to review for this week's quiz and and access what you've learned when you want to refer back to it for future assignments. 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:
- Explain why beaches in northern California are typically narrower and rockier than those in the southern part of the state, and why beaches in both areas are commonly narrower during the winter.
- Predict where waves approaching a rugged coastline will tend to concentrate their energy and where they will tend to disperse it based on how they are refracted as shown by the wave rays in Figure 15.5. (Hint: A wave ray traces the path of the energy in a moving parcel of water, and closely-spaced rays indicate the concentration of a wave's energy whereas widely spaced rays indicate the dispersal of its energy.)
- Predict the likely direction of longshore transport along a beach where the waves are approaching from a given direction. (Hint: See Figure 15-11 on p. 410.)
- Briefly explain why sand carried to the coast by the Ventura River is unlikely to be found on beaches south of about Point Hueneme, and tell where this sand ends up being deposited. (Hint: See Figure 15-12 on page 411.)
- Distinguish a submergent coastline from an emergent coastline based on the typical features each displays (e.g., estuaries, stacks, arches, wave-cut terraces) and describe what each indicates about the rate of local uplift or subsidence relative to the change in sea level.
- Predict the likely effect on coastal erosion "down coast" (in the direction of longshore transport) from (a) building a breakwater; and (b) removing a dam on a river that empties into the ocean.
Reading and Browsing Assignment
- Read Chapter 15, focusing on the topics outlined in the learning objectives above.
- Wave motion, wave refraction, and longshore transport are are just a few of the coastal processes that are hard to get a good feeling for from still pictures. Fortunately there are some great animations of these processes on the web. To see wave motion and refraction check out this flash animation from Washington. To see how longshore transport works check out thin animation from South Carolina. To see how waves produce summer and winter differences in beaches or how wave-cut terraces develop check out these animation from Santa Barbara. (On the last animation I found that the Flash version worked better than the Quicktime version.)
- To see how the construction of structures such as breakwaters, groins, and jetties that interfere with longshore transport of sand will tend to widen beaches on their up-drift sides and erode them on their down-drift sides, check out this discussion of the effect of groins along the South Carolina coast.
- The rise in sea level predicted to accompany global warming has the potential to dramatically affect California's coast and the lives of those who live near it or depend on water from the Sacramento-San Joaquin delta. To learn more, check out this recent report from the Pacific Institute.
- Finally, for a look at the diversity of California's coastline browse some of the aerial photographs available online at the California Coastal Records Project.
Exercise 15: Tsunami and Storm Surge (Due by 9:00 AM on 2-May-2011)
Earthquakes throughout the Pacific Ocean and landslides on oceanic islands like Hawaii have the potential to generate tsunamis that could reach the California coast. In order to learn a little more about this threat as well as that potentially posed by surges from tropical storms moving north from Baja, please load you Hazard City CD and work through version 3 of the Tsunami/Storm Surge project. This is one of the more straightforward Hazard City assignments, and it will probably take you about an hour to complete. Be sure to jot down any notes on the procedure you followed and have the report form printed and filled-in before you go to the Tasks and Tests area of the Etudes site to complete Exercise 15. Also, note the following: (1) to calculate the speed of the tsunamis I simply printed the page containing the map and made my measurements right on the paper—doing so, I obtained a value between 380 and 390 mph for the Valdez tsunami rather than the value given by the authors; and (2) people's homes are evenly distributed throughout Ocean Village. Finally, there are only six questions on this week's exercise so, to make the total come out to 10 points each will be worth 1.67 points.
Quiz 15: California's Coast (Due by 9:00 AM on 2-May-2011.)
After you feel you have met the learning outcomes outlined above please complete Quiz 15 in the Etudes "Assignments, Tests, and Surveys" tool. There are ten questions about the California's coast and the processes that are shaping it, and each is worth one point. If you can answer all of them correctly it means that you know your way around the coastal geology pretty well and are ready to start learning about California's Transverse Ranges next week. Like all of our weekly quizzes, this one is timed (you'll have 30 minutes) and must be completed in one "sitting". (That is, you will only be granted access once.) So, be sure you're ready to complete your quiz when you start it—and be sure you're using Firefox. Good luck.