Chapt. 11 GEOL 110
Long Beach State
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This 3 page Class Notes was uploaded by Elizabeth Rubio on Wednesday April 20, 2016. The Class Notes belongs to GEOL 110 at California State University Long Beach taught by Ewa Burchard in Spring 2016. Since its upload, it has received 6 views. For similar materials see Natural Disasters in Geology at California State University Long Beach.
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Date Created: 04/20/16
420 Waves cont. (slide 15) Variations along a coastline Irregularities in topography ocean floor and coast cause variations in wave height as it approaches shore A single wave is called a wave front Irregular Coastlines have headlands The shape of the coast is similar underwater to that of the coastline Water gets progressively shallower close to shore As the wave approaches the shore, it slows at the headland first This causes the wave front to bend around the headland (refraction) •Effects of wave refraction –Wave normals, perpendicular to wavefronts pointing toward shoreline –Wave refraction causes normal to converge and diverge –Convergence •Wave heights and energy increases •Waves are bigger here –Divergence •Wave heights and energy decreases •Breaking waves –Plunging breakers •Waves that pick up quickly •Typical on steep beaches •More erosive –Spilling breakers •Waves that spill gently •Typical on wide, flat beaches •More likely to deposit sand Beach Form and Processes •Beach consists of loose material which has accumulated by wave action on shoreline •Type of beach material depends on source of sand –White beaches from shell and coral (Pacific Islands) –Black beaches from volcanic rock (Hawaii) –Brown beaches from quartz and feldspar (Carolina) •The beach onshore –Landward extent of a beach on seashore or lakeshore •Line of sand dunes •Line of permanent vegetation or Sea cliff or bluff forms from erosion of rock or sediment –Beaches are divided into •Berm –Beach portion that slopes landward and formed by deposition of sediment by waves •Beach face –Beach portion that slopes toward water –In the swash zone where waves swash and backwash •The beach offshore –Swash zone •Zone where waves swash and backwash on the beach –Surf zone •Where turbulent waves move after waves break –Breaker zone •Where the waves become unstable, peak, and break •Longshore bar forms beneath breakers •Longshore trough forms landward from bar •Sand transport –Littoral transport •Sand movement parallel to shore •Beach drift –Sand moving in zigzag pattern in swash zone •Longshore drift –Transport of sand by longshore currents –Longshore currents •Current that flows parallel to shoreline as a result of up & back movement of water in swash zone –Updrift and downdrift •Indicate the direction in which sediment is moving or accumulating along the shore 11.3 Sea Level Change •The level of the sea is constantly changing •Relative sea level –Position of the sea at the shore –Influenced by movement of both the land and water •Eustatic sea level –Global sea level –Controlled by processes that affect overall volume of water in the ocean and shape of the basins •Eustatic sea level (global sea level) –Rises or falls when the amount of water in the world’s oceans increases or decreases –Climate/average air temperature •Temperature increases cause volume of water to expand •Temperature decreases cause contraction of water •Changes in temperature cause ice on land to melt or snowfall to increase –Volume of water in ice sheets, glaciers increases, ocean water linked –Tectonic processes •Changes ocean basin shape over long period of time •Relative sea level –Glacier melt or earthquakes can cause uplifting of land •Decrease in sea level –Rates of deposition, erosion, or subsidence makes the level rise or fall –Tides caused by gravitational pull of the moon cause daily and seasonal changes –Weather conditions •Changes in wind speed –High winds pile up water and increase water height in open water –Swell increases both water level and wave heights when it reaches the shore •Changes in atmospheric pressure –Can add a meter or more to height of storm surge
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