Characteristics of WavesCharacteristics of Waves► Parts of a wave

Crest – top of the wave Trough – low area between waves

► Measurements of a wave Wave height – the distance between a trough and a crest Wavelength – the horizontal distance between crests Wave period – the time interval between the passage of

two successive crests

► Height, length, and period of a wave depend on Wind speed Length of time wind has blown

► FetchFetch – the distance that the wind has traveled across open – the distance that the wind has traveled across open waterwater

Types of WavesTypes of Waves► Wave of oscillationWave of oscillation

Wave energy moves forward, not the Wave energy moves forward, not the water itselfwater itself

Occur in the open sea in deep waterOccur in the open sea in deep water

Types of WavesTypes of Waves► Wave of translationWave of translation

Begins to form in shallower water when the water-Begins to form in shallower water when the water-depth is about one-half the wavelength and the wave depth is about one-half the wavelength and the wave begins to “feel bottom”begins to “feel bottom”

► As the speed and length of the wave diminish, the wave As the speed and length of the wave diminish, the wave grows highergrows higher

► The steep wave front collapses and the wave breaks along The steep wave front collapses and the wave breaks along the shorethe shore

Turbulent water advances up the shore and forms surfTurbulent water advances up the shore and forms surf

Wave refraction (Bending of a Wave refraction (Bending of a wave)wave)

► Causes waves to arrive Causes waves to arrive nearlynearly parallel to parallel to the shorethe shore

► Consequences of wave refractionConsequences of wave refraction Wave energy is concentrated against the sides Wave energy is concentrated against the sides

and ends of headlandsand ends of headlands Wave energy is spread out in bays and wave Wave energy is spread out in bays and wave

attack is weakenedattack is weakened► Produce longshore currentsProduce longshore currents

Currents in the surf zone that flow parallel to the Currents in the surf zone that flow parallel to the coastcoast

► Easily moves fine suspended sand and rolls larger sand Easily moves fine suspended sand and rolls larger sand and gravel along the bottomand gravel along the bottom

Wave ErosionWave Erosion

►Breaking waves exert a great forceBreaking waves exert a great force Grad students at SUNY SB actually using Grad students at SUNY SB actually using

seismograph to record impactsseismograph to record impacts

►Wave erosion is caused byWave erosion is caused by Wave impact and pressureWave impact and pressure Abrasion by other rock fragmentsAbrasion by other rock fragments

Wave ErosionWave Erosion

►Over time, wave erosion straightens Over time, wave erosion straightens an irregular shorelinean irregular shoreline

►Caused by moving sand along the Caused by moving sand along the beachbeach Waves that reach the shoreline at an Waves that reach the shoreline at an

angle cause the sediment to move along a angle cause the sediment to move along a beach in a zigzag pattern called beach beach in a zigzag pattern called beach driftdrift

Features of a shorlineFeatures of a shorline

►Vary depending on several factors Vary depending on several factors including:including: The rocks along the shoreThe rocks along the shore CurrentsCurrents Wave intensityWave intensity Whether the coast is stable, sinking, or Whether the coast is stable, sinking, or

risingrising

Features caused by wave Features caused by wave erosionerosion

► Wave-cut cliffsWave-cut cliffs► Wave-cut platformWave-cut platform

► Features associated Features associated with headlandswith headlands

► Sea archSea arch► Sea stackSea stack

Features related to beach Features related to beach drift and longshore currentsdrift and longshore currents

► SpitsSpits- Elongated ridges of sand extending from the land - Elongated ridges of sand extending from the land into the mouth of an adjacent bayinto the mouth of an adjacent bay Often the end of a spit hooks landward in response to wave-Often the end of a spit hooks landward in response to wave-

generated currentsgenerated currents

► Baymouth barBaymouth bar – a sand bar that completely crosses a – a sand bar that completely crosses a baybay

► TomboloTombolo – a ridge of sand that connects an island to the – a ridge of sand that connects an island to the mainland or another islandmainland or another island

► Barrier islandsBarrier islands Mainly along the Atlantic and Gulf coastsMainly along the Atlantic and Gulf coasts Low ridges of sand that parallel the coast 3 to 30 kilometers Low ridges of sand that parallel the coast 3 to 30 kilometers

offshoreoffshore

Three Basic Responses to Erosion Three Basic Responses to Erosion Problems:Problems:

► Building structuresBuilding structures JettiesJetties

► Usually built in pairs Usually built in pairs to develop and to develop and maintain harborsmaintain harbors

► Extend into the ocean Extend into the ocean at the entrances to at the entrances to rivers and harborsrivers and harbors

Three Basic Responses to Erosion Three Basic Responses to Erosion Problems:Problems:

► GroinsGroins Built to maintain or widen beachesBuilt to maintain or widen beaches Constructed at a right angle to the beach Constructed at a right angle to the beach

to trap sandto trap sand

► BreakwaterBreakwater Barrier built offshore and parallel to the Barrier built offshore and parallel to the

coastcoast Protects boats from the force of large Protects boats from the force of large

breaking wavesbreaking waves

► SeawallSeawall Barrier parallel to shore and close to the Barrier parallel to shore and close to the

beach to protect propertybeach to protect property Stops waves form reaching the beach Stops waves form reaching the beach

areas behind the wallareas behind the wall

► Often the building of structures is not Often the building of structures is not an effective means of protectionan effective means of protection

Three Basic Responses to Erosion Three Basic Responses to Erosion Problems:Problems:

►Beach nourishmentBeach nourishment The addition of large quantities of sand to The addition of large quantities of sand to

the beach systemthe beach system Only an economically viable long-range Only an economically viable long-range

solution in a few areassolution in a few areas

►Abandonment and relocationAbandonment and relocation of of buildings away from the beach buildings away from the beach