GEOL 102 1st Edition Lecture 16 Outline of Last Lecture I. IntroII. CurrentsIII. TidesOutline of Current Lecture I. WavesII. Coastal ProcessesCurrent LectureI. WavesWind drag across ocean surfaces causes waves to formMinimum wind speed needed is 2 mphAnatomy of a waveAmplitude (vertical distance): average 2-10 mWavelength (horizontal distance): 10-500 mVelocity: 20-60 mphThe depth of the wave base, where oscillatory movements underwater are no longer active, is about half the wavelengthWave character depends on:Wind velocityFetch: the distance the wind blowsHow to make a breaker1. below wave base, water is undisturbedThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. wave base touches sea floor as wave approaches coast3. wave velocity decreases4. wavelength decreases and amplitude increases5. wave base slows and wave crest overruns base – it breaksWave refractionDeeper waves travel faster than shallow onesWaves “pivot” around obstructionsExtreme WavesTravels thousands of miles beyond their originSize depends on wind speed, distance air has travelled across surface (fetch), and the depth of waterWaves can combine to form extreme wavesTsunamisBegin at sea as short amplitude, long wavelengthLongshore CurrentsWaves approach coast at angle and return straight outwardCoast-parallel flow resultsLongshore drift: transport of particles along this trajectoryRipcurrentsWater builds up in surf zone, pressure is released locally via “channels”II. Coastal ProcessesWave energy14,000 waves hit a given section of coast every dayCoastal erosion depends on:1. rock properties2. slope of seafloorgradual- waves break offshore3. Wind orientationCoastal landscape factorsSea level changeTectonic settingSediment inputBeachesSediment-rich coasts with gentle slopesMost are sandy – coarser particles are easily broken downBeach featuresLongshore drift can generate: sand spits, baymouth bars, offshore bars, barrier islandsBeach sediment budgetSediment is added by: rivers, wind, waves, longshore driftSeasonal variations in wave properties affect beach characterIn winter, shorter wavelength waves cause a shallow wave