THE SURF ZONEA photo tour of selected beaches to illustrate: • Plunging and spilling breakers • Longshore currents • Rip currents • Undertow Shoreline Community College Oceanography 101 Linda Khandro
HOW TO PROCEED• First of all, study ALL the pictures and videos of the surf and beach slope formations in this Power Point. Take your time and enjoy!• STOP when you get to (about) slide 76 with the instructions. This slide and the ones following it, are also attached to the EX6 Assignment page in our Blackboard Week 6 folder. Download and save the file from Blackboard to your hard drive, labeling as usual: lastname_ex6.doc.• Print that file for easy reference as you go through these pictures and videos again.• Answer all the questions on your new file.• When you come to question D, about “rip tides”, rip currents, and longshore currents, BE SURE to go back to slide 74. There you must open the links to see and hear about the formation of rip currents from longshore currents.• Finish answering the questions on your file and attach to the Blackboard Assignment page.• You’re done! Now watch out for rip currents and undertow!
Some beaches of Baja, Mexico:The west side is on the PacificOcean, the south point of Baja isbetween the Pacific and the Seaof Cortez, and the east side is onthe Sea of Cortez.Some of these slides are videos. Mouseover the slide until the white box showsup at the bottom. Click on the arrow atthe bottom left side.
Beach at El PozoHondo, nearTodos Santos(west side)…
Los Cerritosbeach, nearTodos Santos(west side)…
Beach at PlayaGrande, nearCabo San Lucas,south point ofBaja
Beach at CaboPulmo, east sideof Baja (Sea ofCortez)…
Some beaches of Yucatan,Mexico: Puerto Morelos andCancun are both on the Caribbeanside of the Yucatan Peninsula.Some of these slides are videos. Mouseover the slide until the white box shows upat the bottom. Click on the arrow at thebottom left side.
Puerto Morelosbeach, with theMesoamericanReef offshore(white surf)…
THE SURF ZONE Some important points:1. There are 3 main types of surf, with surging, plungingand spilling breakers, all of which form in response tovarious factors of the beach slope, including thesteepness of the slope. We are discussing only plungingand spilling waves, or breakers, here.2. A steeply sloping beach face can create a strongundertow.3. Converging longshore currents can create rip currents.4. The dangers created by rip currents and undertow arereal, but are not the same.
http://oregonstate.edu/dept/ncs/newsarch/2007/Jul07/ripcurrents.html“If you’re looking out toward the waterand you see the long-shore current comingfrom both the left and right, there’sprobably a rip current in front of you.”http://www.nytimes.com/interactive/2009/01/06/science/20090106-sandslide/index.html
INSRUCTIONS FOR THE EXERCISE:Now download and print the Blackboard EX6Assignment page! If you already have it, you’re ready togo back to the beaches slides above, then answer thequestions on the Assignment page.Use your Textbook pages 210-211 and the Glossarypages 420 & 423 for further reference to plunging andspilling breakers.The following 7 slides just re-state the questions. Typeyour answers onto the page you have labeledlastname_ex6.doc.
A. Plunging Breakers1. Which of the beaches illustrate, for themost part, “plunging” breakers? Name thebeaches as they are labeled on the slides.2. Which of the beaches with plungingbreakers clearly show(s) a steep beach face?3. What is the significance (or relationship)of this kind of beach slope with respect tothe plunging breakers?
B. Spilling Breakers1. Which of the beaches illustrate, for themost part, “spilling” breakers? Name thebeaches as they are labeled on the slides.2. What is the general slope of thesebeaches?3. What is the significance (or relationship)of this kind of beach slope with respect tothe spilling breakers?
Reef Breakers: In the Puerto Morelos Reefpictures, you can see surf breaking on anoffshore reef.1. What kind of breakers are these,plunging or spilling? If you can’t tell fromthe photos, consider that the reef has afairly steep slope on the seaward side.
D. Rip (tides or currents?) At PlayaGrande beach, you will see a red warningsign (previous slide) advising guests not toswim due to the Rip Tide there.1. Define Rip Tide (if you can!).2. Define Rip Current. What kind of beachprocess must be present for a rip currentto form? If in doubt, see Slide 78 again.
3. According to the beach photosthemselves (not the sign), do you seeevidence of a Rip Current at Playa Grande?4. If there is no Rip Current at PlayaGrande, how else would you warnpotential swimmers here? Look again atthe seaward flow of water after the surfbreaks; look at the slope of the beach faceand think about the fundamental force ofnature which creates that flow of water.
5. What name (or names) do we give to that seaward flow of water? 6. What is the fundamental force ofnature that creates the danger at this beach?