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.

next

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