GEOL 108Lg 1st Edition Lecture 13Outline of Last Lecture- What is mass wasting?a. Mass wasting phenomena, causes-Weathering- Efect of Water- Controls on Mass WastingOutline of Current Lecture- Hurricanesa. Mass wasting phenomena, causes- WavesCurrent LectureThe Cape Hatteras LighthouseWaves are caused by wind moving fast over relatvely slow moving water bodyMagnitude depends on speed, duraton of wind, and fetch of wind (the area or distance blownby winds)Waves and wells (wave groups formed at sea)When you characterize waves it’s important to recall the parameters we use to defne any ways amplitudedifference between crest & troughthe wave length (difference between two crests/two troughs)-In shallower water at depth less than 0.25 L the orbits become elliptcal (partcularly when water depth is less than 0.05 L)-At the bottom, moton may be horizontal, forward and back.-The wave goes slower when the water depth goes down.-Tsunami’s are caused by earthquakes or other seafloor movementsWave and Water movement-Swell: The wave groups generated by storms far out at sea-As the swell enters shallower water, transformations take place that eventually lead to the waves breaking on the shore-Wave energy is approximately proportonal to the square of the wave height. Thus if wave height increases to 5 m (16 ft), increases 52, or 25 tmes over that of waves with a height of 1 m (3.3 ft)-Waves are unstable when the wave height is greater than about 10 percent (0.1) of thewave length.Sand-beach-water interactionsThe more salt you have, the denser the water.Waves refracton is the reason that often when you go on the beach where the waves break on protruding rock.Wave EnergyWaves expend their energy along the coastlineWave translaton: decrease the wave length and veolcity but increase in wave heigh; deep water wave energy translatng into wave breakers, pounding the shore wave refracton: the bending of waves (convergence) towards the protruding areas (headlands)Rip Current SlideA rip current is a narrow, powerful current of water running perpendicular to the beach, out into the ocean. They drag you out to sea at top speeds. We want to protect the beach - a breakwater is a solutonDetached breakwater - A barrier built out into the sea to protect a coast or harbor from the force of waves.Erodes beach in other areasBeach GroinsYou end up with very uneven distributonSof Stabilizaton: beach nourishmentNourishment: trucking sand into places that would naturally be erodedCreatng an artfical beachAlternatve to coastal engineering structureConstructng a positve beach sand budgetSand BudgetHuman actvites have resulted in greater rates of erosion and more sediment carried by
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