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.

Shoreline Features and ProcessesChapter 16, Section 3

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

Impact and Abrasion

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

Wave Refraction

Concept CheckWhat is wave refraction?The bending of waves

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

Longshore Currents

Concept CheckWhat causes longshore currents?The angling of waves in the surf zone

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

Wave-Cut Cliffs

Sea Arches

Concept CheckHow does a sea arch form?Sea arches form when two caves (eroded by surf) on opposite sides of a headland unite.

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

Spit, Bars, and Tombolos

Barrier Islands

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.

Evolution of Shoreline Features

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

Protective Structures

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!!!

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.