beaches i intro a. beaches= elongate ribbons of sand b. source of sand = mostly rivers c. protect...
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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 shoreC. Nearshore subdivision = backshore,
foreshore & offshore1. backshore--submerged during highest
tide,strong storms2. foreshore--extends past low tide3.offshore--low tide to limit of wave reworking
II. ANATOMY
D. Berms where 1. foreshore/backshore meet
2. form by shoreward deposition3. have higher elevation or slope4. high berms = winter; lower
berms = summer5. have flat top, maybe ridge or
berm crest
E. Wave-cut terraces1. flat beveled surface2. formed by waves & moving
sediments
F. Troughs & bars parallel shore1. 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 riversi.armored beach covered by stones
4.Color
IV. BEACH PROCESSES
A. Equilibrium1.material brought in = material removed
B. ProcessesBeaches change with time
1. grow in summer
2. diminish in winter
3. storms induce major changes
SUMMER / WINTER BEACHES
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
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JETTIES AND GROINS
Jetties and groins trap sand that would otherwise be moved along the shore by wave action.
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LONGSHORE CURRENT
Santa Barbara
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SANTA BARBARA HARBOR
IV. BEACH PROCESSES
Processes (con’t)D. Rip Currents & Littoral Cells
1. rip currents--fast and seaward moving currenti. sediment deposited in offshore
2. cycle of sediment transport along shorei. sediment to beach
ii. along beach
iii. back to sea
iv. cycle part of littoral cell
RIP CURRENTS & LONGSHORE DRIFT
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.edu/sumner/gel109/SedStructures/Lg/BeachXStrat3.jpg
http://mygeologypage.ucdavis.edu/sumner/gel109/SedStructures/Lg/BeachXStrat3.jpg