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Warm Up 2/27/08Which of the following is a tidal current?a.
spring tidec. neap tideb. flood tided. both a and cThe smallest
daily tidal range occurs during which type of tide?a. spring tidec.
neap tideb. flood tided. ebb tideWhich tidal pattern has two high
tides and two low tides each day?a. semidiurnalc. mixedb.
bidiurnald. diurnalAnswers: 1) d. 2) c. 3) a.
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Shoreline Features and ProcessesChapter 16, Section 3
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Forces Acting on the ShorelineWaves along the shoreline are
constantly eroding, transporting, and depositing sediment. Many
types of shoreline features can result from this activityThe impact
of large, high-energy waves against the shore can be very
violentCracks and crevices quickly open in the cliffs, and water is
forced throughAbrasion is the sawing and grinding action of rock
fragments in the waterWaves are also very effective at breaking
down rock material and supplying sand to beaches
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Impact and Abrasion
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Wave RefractionWave Refraction the bending of wavesMost waves
move towards the shore at an angleWhen the waves get closer, they
are refracted, bent, so that they come into the shore
parallelBecause of refraction, wave energy is concentrated against
the sides and ends of headlands that project into the water,
whereas wave action is weakened in bays
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Wave Refraction
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Concept CheckWhat is wave refraction?The bending of waves
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Longshore TransportLongshore Current flow parallel to shore and
move large quantities of sediment along the shoreTurbulence allows
long shore currents to easily move fine suspended sand and to roll
larger sand and gravel particles along the bottomLongshore currents
can change directions because the direction that waves approach the
beach changes with the seasonsLongshore currents generally flow
southwards along the Western coast of North America
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Longshore Currents
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Concept CheckWhat causes longshore currents?The angling of waves
in the surf zone
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Erosional FeaturesShoreline features that originate primarily
from the work of erosion are called erosional featuresWave erosion
is steadily wearing away the California coastThe cliffs along our
coast are created when tectonic processes push the land up at the
same time the ocean waves crash against them, eroding them
awayWave-cut cliffs result from the cutting action of the surf
against the base of coastal landAs erosion continues, it will
reduce the cliffs into a bench-like feature, called a platformThe
surf can erode headlands, creating sea caves, when two sea caves
meet, a sea arch will formArches all eventually collapse into sea
stacks
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Wave-Cut Cliffs
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Sea Arches
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Concept CheckHow does a sea arch form?Sea arches form when two
caves (eroded by surf) on opposite sides of a headland unite.
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Depositional FeaturesSediment that is transported along the
shore and deposited in areas where energy is low produce
depositional featuresWhere longshore currents and other surf zone
currents are active, several features related to the movement of
sediment along the shore may developA spit is an elongated ridge of
sand that projects from the land into the mouth of an adjacent
bayThe term baymouth bar is used when a sandbar completely crosses
a bay, cutting it off from the ocean A tombolo is a ridge of sand
that connects an island to the mainland or another islandBarrier
Islands narrow sandbars parallel to, but separated from the
coast
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Spit, Bars, and Tombolos
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Barrier Islands
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Concept CheckWhat is a barrier island?A barrier island is a
narrow sandbar parallel to, but separate from, the coast at
distances from 3 to 30 km offshore.
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Evolution of Shoreline Features
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Stabilizing the ShoreShorelines are among Earths most dynamic
places and are changing constantlyErosion along the coast causes
significant property damage every yearGroins, breakwaters, and
seawalls are some structures built to protect a coast from erosion
or to prevent the movement of sand along a beachA groin is a
barrier on the beach to trap sand that is moving parallel to the
shoreA breakwater protects ships from the force of large breaking
waves as they pull out of harborA seawall is built parallel to
shore and protects the shore from wavesBeach nourishment is the
addition of large quantities of sand to the beach system
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Protective Structures
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Assignment (Due 2/28/08)Read Chapter 16 (pg. 448-467)Do Chapter
16 Assessment #1-30 (pg. 471-472)Study for the UNIT TEST!!!
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Cool DownWhat structures can be built to protect a
shoreline?Groins, breakwaters, and seawallsHow can beach
nourishment be helpful? How can it be harmful?Beach quality and
storm protection are improved. The process is expensive and can
harm local marine life.What is one thing new you learned today?
Explain.