Reading Guide #9 -- Coasts

Unfortunately, we won't have time to cover everything in this chapter; we will only cover the coasts part of it. Therefore, you can skip pp. 369-376, and start reading about Ocean Tides on p 377. For pp 378-384, try to figure out the list of ingredients for making a beach. Remember from lecture about tides, waves, and a sediment supply. These are all covered in this chapter.

Tides: Why are there two high and two low tides per day? See fig 13.7. On some coastal systems, especially those with barrier islands, the tides are a very important energy source.

Waves: Why do they break? See fig 13.11. Note that the geologic significance of waves is that they provide energy to move sand about on the beach. What is wave refraction and why does it happen? On fig 13.13, why is there a beach in the bay, but not on the headlands, and what does that have to do with wave refraction? What is the relationship bewteen figs 13.12 and 13.14?

Sediment supply: Everywhere the book talks about erosion is a source of sediment, in addition to the rivers and seacliffs we talked about in class. The key is that for most places on the beach, as the waves erode, the sand is immediately replaced by long-shore currents.

Where does the sand go? Down submarine canyons, of course; see fig 13.16. Around Santa Cruz, much of the coastal sediment is destined for the Monterey Canyon.

Variety of Coasts

We talk abou this a lot in class. In fact, even the same images are used in Skinner and Porter. See fig 13.19, for example. The concept of a wave-cut platform (or bench) is an important one because it leads to terraces.

Make sure you see fig 13.22, as it explains the development of barrier islands, which are important on the east and gulf coasts. Make sure you read pp 388-389 on this subject. Fig 13.24 is a beautiful example of a barrier island. We son't go into figs 13.25 and 13.26 in class, but they nicely illustrate where volcanoes go to die.

Coastal Evolution

Make sure you understand the concepts of submergence and emergence on pp 392-394. Fig 13.29 is a world-class example of terraces.

Coastal Hazards

Understanding these, and the protections against them, should be fairly intuitive after study of the preceeding pages. Fig 13.33 is what a barrier island looks like after development; compare with fig 13.24. What might Miami Beach look like during a hurricane (the team name of the University of Miami)? What are those groins designed to do in fig 13.33?