Oceans and Coasts & Shorelines low tide to high tide Active Margins - coincide with a plate boundary Passive Margins - do not coincide with a plate margin great quantities of sediment are often trapped along shorelines Significance of Shorelines approximately 67% of the Earth's population live in a narrow belt parallel to the coastlines. processes taking place along a shoreline play a major role in determining what happens to this population. Waves Waves can be created when wind moves across the surface of a body of water Fetch - the distance the wind blows - The greater the fetch the greater the size of the wave Waves can be created by any process that displaces the body of water - earthquakes, for example - Tsuanami Waves Until they are close to shore, the water molecules move up and down The speed of a wave (the clerity) is the wavelength/period the wavelength is the distance from crest to crest or trough to trough the period is the time between adjacent crests Wave Base the wave base is 1/2 of the wavelength - if the wavelength is 6 feet, the wave base if 3 feet. when the water depth is less than the wave base, the wave is slowed down as it begins to interact with the bottom of the basin. Wave Refraction is initiated. Wave Refraction Breakers form when the wave base is reached the waves begin to bend because part of a wave front may be affected by wave base whereas the other part is not .... a Longshore current develops which moves parallel to the shoreline Tides The positions of the Earth, Moon and Sun control the location of the tides the effect of the moon is the dominate factor If the Earth - Moon separation distance decreased, what would happen to the tides? Environments of Accumulation Beaches - low tide to high tide Spits - sand bar extends into a body of water - such as Cape Cod, MA Barrier Islands - parallel to the coast line - when sea level rises the barrier islands move inland. Off Shore Plate Tectonics Spreading Centers Deposition in Deep Water A continental component - delivered by turbidity currents - submarine canyons a Pelagic component - sediment suspended in the water column - CCCD