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The Marine Environment CH. 16 Shoreline Features • Shorelines are shaped by waves, tides, & currents. Erosional Landforms • Water is a strong agent of erosion • It acts greatest on rocky headlands, which occurs through wave refraction. – Wave Refraction is the bending of wave crests and focusing them on the headlands. Landforms Created By Wave Refraction • Sea Stacks are created as weaker surrounding rocks are broken and eroded away. • Sea Arches are formed as strong rocks are undercut by waves. • Sea Caves form as breakers erode into cliffs. Beaches: • Beach: A sloping band of sediment at the edge of the sea. • Composed of loose sediment deposited and eroded by waves. • Composition and color depends on parent material. Estuaries: • Estuary: Brackish water where a freshwater stream meets the sea. – Makes for great fish nurseries. – Example: Chesapeake Bay Longshore Currents: • As you walk out to sea, the water gets deeper and then shallow again. – The deep part is called a longshore trough. – The shallow region is a sand bar called the longshore bar. • This creates a channel of water that runs parallel to the shore, called a longshore current • Rip Tides form when water flows out to sea through holes in the longshore bar. – These are dangerous!!! Depositional Features: • Longshore currents form many features: – Spit – Baymouth bar – Barrier Islands: Long ridges of sediment deposited by longshore currents. • These can connect with the mainland and form peninsulas. Changes in Sea Level • Sea levels have been rising since the last ice age ended. • Effects of Sea Level Changes: – Many coastal features will disappear if sea levels continue to rise. • There is a potential for sea levels to come up 70 m. The Seafloor Oceanic and Continental Crust • As continents rise up from the ocean floor, a section of them is covered by the water. – Continental margins are the submerged parts of continents. • The continental margin is made of the continental shelf, continental slope, and continental rise. Continental Shelves • Continental Shelf: The shallowest part of a continental margin. Continental Slopes • After the continental shelf, the seafloor begins to quickly drop. – This is the Continental Slope • The true edge of a continent. • Erosion from the continental slope causes turbidity currents, which cut canyons into the ocean floor. – Deposits from a turbidity current for the continental rise. Ocean Basins • The ocean basin is a deeper part of the seafloor that lies above the oceanic crust. – Basins are covered in pretty interesting topography. Abyssal Plains: • Plains covered in fine-grained sediments • Deep Sea Trench: Depressions in the seafloor Mid-Ocean Ridge: • Mountain chains that run through ocean basins. – Here, there are many volcanic eruptions and earthquakes. Hydrothermal Vents: Holes in the seafloor through which water heated by magma flows. Seafloor Volcanoes • Most mountains on the ocean floor are extinct volcanoes. • 2 types: – Seamounts: volcanoes more than 1 km high – Guyots: volcanoes with flat tops. Marine Sediments • Most marine sediment comes from the continents. – Tends to be fine-grained sediment called deep-sea mud. • Ooze: Sediment containing a large percentage of particles derived from once-living things.