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test 2 notes - Lecture#8 Chpt 10 Coastal Processes Geology...

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Lecture #8 Chpt 10 Coastal Processes Geology 106 Spring 2008 Introduction Oceans cover 70% of the Earth The coastline meeting place of land and water is one of the most dynamic areas on the planet’s surface. The defining attribute of coastal zones is CHANGE! We seek the comforting constancy of waves breaking on shorelines and so we build close to the edge -- but we also want stasis after we build. .. Yet beaches, bays and coastal dunes are in constant motion - Shorelines and headlands retreat and advance - Waves keep pounding -coastal currents keep flowing - and then the big winds and tidal surges come When hurricanes cut barrier islands into pieces and move beaches wholesale, we want our shorelines “restored”. The US has 150,000 km (90,000 miles) of coastline (including the Great Lakes) In 1990, 50% of the US population could reach a coastline in less than a one hour drive from their home. It’s the same old story - As more people live and visit coastal areas, the risk of exposure to “coastal hazards” that are a part of the natural processes of coasts will increase Coastal Processes Waves - wind blowing over water transfers some energy to the water and creates waves Wave size is determined by: - wind velocity - length of time the wind blows over the water - the distance over open water (fetch) that the wind blows Swells - groups of long, even-spaced waves generated by sea storms - they eventually become big breakers on distant shorelines Deep Water vs Shallow Water Waves
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Water particles move in circular pattern. Circles become smaller until a depth of L/2. (L = wavelength) In water depths less than L/4 water particles move in elliptical pattern. Waves & Coastlines As waves move into shallow water, the sea floor interferes with the water particles - wave velocity decreases due to friction ------> wave height increases and finally forms breakers (surf) Erosion by waves- Wave refraction – The part of the wave that “feels bottom” first, slows down The part still in deeper water moves forth and the entire wave line curves, forcing wave energy towards headlands Irregular coastlines give rise to energy concentration which increases erosion on headlands and energy dissipation (deposition) in embayments Wave refraction – waves approaching a shoreline at an angle are bent or refracted - this creates a current parallel to the shore - a longshore current = a zone of faster moving water that creates a longshore drift of sediment Rip currents kill 200 people each year in the US Speeds up to 4 mi/hr seaward Don’t panic! Swim parallel to shore until free of the current Beaches - depositional shoreline features made up of sand and/or gravel accumulated by wave and current action Sand beaches - white, black, brown. .. sources -
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test 2 notes - Lecture#8 Chpt 10 Coastal Processes Geology...

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