BEACHES

I Intro A. Beaches= elongate ribbons of sand B. Source of sand = mostly rivers C. Protect coastline D. Form mostly in low tide areas, with sand source E. Mostly well sorted, rounded, qtz rich deposits

II. ANATOMY A. Shore= seaward lowest tide to waves influence on land B. Beach = sand/sediment along shore C. Nearshore subdivision = backshore, foreshore & offshore 1. backshore--submerged during highest tide,strong storms 2. foreshore--extends past low tide 3.offshore--low tide to limit of wave reworking

Thurman Essentials of Oceanography 6/e

II. ANATOMY D. Berms where 1. foreshore/backshore meet 2. form by shoreward deposition 3. have higher elevation or slope 4. high berms = winter; lower berms = summer 5. have flat top, maybe ridge or berm crest E. Wave-cut terraces 1. flat beveled surface 2. formed by waves & moving sediments F. Troughs & bars parallel shore 1. bars grow during winter, worn away in summer

III. BEACHES & VARIATIONS A. Beaches classified by: 1.Shape & structure - wide,narrow, long, discontinuous 2.Composition - shell, lava, pebbles, shingles (flat pebbles-slide back & forth) 3.Size of materials - sand or cobbles (nearby source)--sand from rivers i.armored beach covered by stones 4.Color

IV. BEACH PROCESSES A. Equilibrium B. Processes 1.material brought in = material removed B. Processes Beaches change with time 1. grow in summer 2. diminish in winter 3. storms induce major changes

SUMMER / WINTER BEACHES Thurman Essentials of Oceanography 6/e Differences between summertime and wintertime beach conditions can be seen at Boomer Beach in La Jolla, California.

IV. BEACH PROCESSES Processes (con’t) C. onshore currents= onshore transport 1. longshore transport--current moves down beach, caused by waves hitting beach at angle 2. longshore currents transport sediment 3. sediment on beach moves in zig-zag fashion--swash/backwash

LONGSHORE CURRENT next Earth: An Introduction to Physical Geology, 7e - Tarbuck & Lutgens A longshore current, caused by refracting waves, moves water in a zigzag fashion along the shoreline. This causes a net movement of sand grains, also in a zigzag fashion, from upstream to downstream ends. After Tarbuck, E. J., and Lutgens, F. K., The Earth: An Introduction to Physical Geology, 4th Ed. (Fig. 14.8), Macmillan Publishing Company, 1993 next

JETTIES AND GROINS Jetties and groins trap sand that would otherwise be moved along the shore by wave action. Reprinted by permission from Tarbuck, E. J., and Lutgens, F. K., Earth science, 5th Ed., Merrill Publishing Company, 1988. Jetties and groins trap sand that would otherwise be moved along the shore by wave action. next

LONGSHORE CURRENT back Thurman Essentials of Oceanography 6/e Santa Barbara Thurman Essentials of Oceanography 6/e Southern California has several beach compartments, which include rivers that bring sediment to the beach, the beach that experiences longshore transport, and the submarine canyons that remove sand from the beaches. Average longshore transport is toward the south. back

SANTA BARBARA HARBOR Thurman Essentials of Oceanography 6/e Construction of a breakwater at Santa Barbara Harbor interfered with the longshore drift, creating a broad beach. As the beach extended around the breakwater into the harbor, dredging operations were initiated to keep the harbor from being closed off by sand. The placement of dredged sand downstream of the harbor helped reduce coastal erosion there. From U.S. Coast and Geodetic Survey Chart 5161.

IV. BEACH PROCESSES Processes (con’t) D. Rip Currents & Littoral Cells 1. rip currents--fast and seaward moving current i. sediment deposited in offshore 2. cycle of sediment transport along shore i. sediment to beach ii. along beach iii. back to sea iv. cycle part of littoral cell

RIP CURRENTS & LONGSHORE DRIFT Thurman Essentials of Oceanography 6/e

Sedimentary Structures http://www.sciencedirect.com/science/article/pii/S0025322705003981

Sedimentary Structures http://mygeologypage.ucdavis.edu/sumner/gel109/SedStructures/Lg/BeachXStrat3.jpg

http://mygeologypage. ucdavis http://mygeologypage.ucdavis.edu/sumner/gel109/SedStructures/Lg/BeachXStrat3.jpg

http://mygeologypage. ucdavis http://mygeologypage.ucdavis.edu/sumner/gel109/SedStructures/Lg/BeachXStrat3.jpg