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UI CEE 1030 - Land- Sea Boundary
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CEE 1030 1st Edition Lecture 19 Land- Sea Boundary - common boundary between air, land, and ocean - constantly changing (modified Dynamic Interfaces  shoreline- line that marks the contact between land and sea (constantly moving)  coastline- the coast’s seaward edge; landward limit of the effect of the highest storm waves on the shoreMoving Shorelines- the shoreline migrates up and down each day as the tide rises and falls Changing coastlines - storms can result in abnormally high shorelines - coastline marks most inland evidence of ocean waves (the highest shoreline) - coastlines change mainly as result of storm erosion and sea-level change Waves- wind-generated waves provide most of the energy that shapes and modifies coastal zones Anatomy of a wave  crest- high point of a wave  trough- low point between waves Measuring waves wave height- distance between crest and trough  wave length- horizontal distance between crest  wave period- time interval between the passage of two successive crests Predicting wave size These 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.- wave size depends on:  wind speed length of time wind has blown  fetch (distance wind has traveled across open water)  water depth Formation of Surface Waves - wind= force behind most ocean waves - as wind blows, energy is transferred from air to water by pressure and friction - water molecules are displaced in direction of wind, but snap back because of molecular cohesion- result: water particles travel in orbits as wave peaks and troughs “pass by” Oscillation waves= wave form advance as: water particles travel in circular orbits (like a toy boat at the surface) - Oscillation waves occur in open ocean (no blockages, deep water) Effect of water depth- water particle movement decreases with increasing water depth (i.e., radius of orbit gets smaller) - below half a wave length in depth, there is little to no wave action Effects of shallowing - deep water: water particles move in circular orbit from surface to depth - shallower water: water particles move in a circular orbit at surface but are increasingly elliptical toward ocean floor - shallows are slow wave speed, so wave length becomes shorter and crest heights increase - eventually crests become unstable and the steep wave front collapses - as wave crest breaks forward, turbulent water flow increases Translation waves translation wave: turbulent advance of water created by breaking waves in shallows Shore Zones  offshore: seaward of where waves break at low tide  nearshore: zone between where waves break at low tide to low-tide level foreshore: area between low-tide shoreline and coastline; most active area and typically wet backshore: area inland of foreshore, affected by storm waves and atypical high tides, but mainly wind Wave erosion - breaking waves exert great force - wave erosion is cause by:  wave impact and pressure  abrasion by rock fragments Beaches beaches: wave act to accumulate local sediment along the landward margin of an ocean or lake Beach formation - as breaking waves move water up the shore and then back down, sediment is moved and abraded - differential sorting and transport of sediment grains by wind and wave action - inland areas affected primarily by wind transport and occasional storm waves Foreshore feature- vary depending on:  rockiness of shore currents wave intensity tectonic regime Foreshore features  beach face: sloping section of beach below berm - exposed to swash of waves - composed of fine- grained sediment  berm: nearly flat area inland of beach face - stays dry except at extreme high tide - sof dunes: hill or ridge of wind- deposited sand; fine grained relative to shore- dunes can extend inland for miles, or be interrupted by cliffsCostal features - change in sea level relative to land has significant impact on costal features - relative sea level can change slowly (i.e., geologic time scales) or rapidly (e.g., earthquakes) - falling sea level or rising coast results in an emergent coast - rising sea level or a sinking coast results in a submergent coast Emergent coasts - if coast rises or sea level drops, land once covered by sea emerges to form part of the landscape - waves erode surfaces previously below water - wave erosion at sea level undercuts cliffs, leading to collapse of cliff face - over time, cliffs retreat while beach extends at base Features of emergent coasts - jagged cliff face- wave- cut notch - wave-cut platforms - when erosion rates vary, undercutting may initially produce sea caves- when sea caves from opposite sides of a rocky headland meet, a sea arch may form - eventual weakening of sea arch may result in its collapse to form a sea stack Submergent coasts - if sea level rises or land subsides, land once exposed will be submerged by the sea - river valleys are inundated by ocean water and become estuaries - hilly terrains become islands Rising sea level - since 1900, sea level has risen 1-2 mm per year - as global sea level rises, many inhabited areas (including major cities) become submergent coasts - artificial solutions: levees, flood gates, stiltsCoastal erosion and deposition - factors affecting coastal erosion and deposition  degree and type of tectonic activity topography and composition of the land  configuration of coastline and nearshore prevailing wind and weather patterns  proximity to sediment- laden rivers Differential coastline erosion - if coast is composed of rocks of different hardness, different areas will erode at different rates - result in an irregular coastline Bending waves= refraction waves - waves slow as they enter shallow water - where shoreline is curved, wave will “bend” and align with the underwater Wave refraction - consequences:  wave energy is concentrated against sides and ends of headlands  wave energy is spread out and weakened in bays Oblique waves- wind that do not blow perpendicular to the coast cause waves that reach the shoreline at an angle (= oblique waves) - oblique waves cause current to flow parallel to coast in the surf zone, called a longshore current Beach drif - oblique waves and longshore currents move sediment along beach in a zigzag patter (= beach drif) - longshore currents move fine sand in suspension and larger particles by saltation and


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UI CEE 1030 - Land- Sea Boundary

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