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Creation of Seafloor and Coastal Features
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Continental Margins
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Terms to Know Continental margins- shallow water areas close to the continents Passive margins- continental margin that lacks a plate boundary and is marked by a low degree of tectonic activity, such as those typical of the Atlantic Ocean Active margin- continental margin marked by a high degree of tectonic activity, such as those typical of the Pacific Rim
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Continental Shelf Flat zone extending from the shore beneath the ocean surface to a point at which a marked increase in slope angle occurs called the shelf break Made up of granitic continental crust so it is geologically part of the continent Found along continents however average width varies depending on the local geology and topography
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Continental Slope Relatively steeply sloping surface lying seaward of the continental shelf The slope of the continental slope is affected by the type of margin present Passive margins have gentle slopes Convergent active margins have steep slopes due to the trenches
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Continental Rise Gently sloping depositional surface at the base of the continental slope Turbidity currents that move through and erode submarine canyons transports material that exit the mouth of the canyon and settle deposit at the base of the continental slope Only found along passive margins, are NOT found along convergent active margins since continental slope leads to a trench
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Abyssal Plain Flat depositional surface extending seaward from the continental rise or oceanic trenches Formed by fine particles of sediment slowly drifting onto the deep ocean floor Few occur in the Pacific most occur in the Atlantic and Indian Ocean (the convergent active margins in the Pacific prevent the sediment moving past the continental slope)
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Seafloor Features
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Ocean Ridges Long continuous mountain range on the sea floor
Created by sea-floor spreading at divergent boundaries Examples: Mid-Atlantic Ridge, Pacific-Antarctic Ridge, Juan de Fuca Ridge
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Generation of a Divergent Boundary
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Ocean Ridge Video
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Hydrothermal Vent Sea-floor hot springs
Created as cold seawater seeps down along cracks and fractures in the ocean crust is heated by underlying magma and surfaces again through these vents Found all along the mid-ocean ridge
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Hydrothermal Vent
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Hydrothermal Vent Video
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Trenches Deep linear scars in the ocean floor
Caused by the collision of two plates along convergent plate margins (continental-oceanic or oceanic-oceanic) Mariana Trench, Peru-Chile Trench, Aleutian Trench
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Trenches from Oceanic-Oceanic Convergence
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Trenches from Oceanic-Continental Convergence
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Marianas Trench Video
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Ring of Fire—Depths Below
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Underwater Volcanism
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Deep Ocean Volcanoes
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Seamount An individual volcanic peak extending over 1000 meters above the surrounding ocean floor Created due to volcanic activity either from activity at a mid-oceanic ridge, a hotspot, or oceanic-oceanic convergence Example: Hawaiian Islands-Emperor Seamount Chain
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Island A piece of land completely surrounded by water
Formed by volcanic activity West Indies, Antilles, Tobago, Fiji
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Island Chain Group of islands formed by the same geological process
Can either be formed as an oceanic plate moves over a hot spot, or at oceanic-oceanic convergence Hawaii (hot spots); Aleutian Islands (oceanic-oceanic convergence)
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Guyout or Tablemount Seamount with a flat top
As a seamount moves away from its magma source the top can be flattened due to wave action Ex: Gifford Guyot off the coast of New South Wales
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Atoll Ring shaped coral reef surrounded by a lagoon
Coral reef that formed around a volcano which remains and continues to grow after the volcano has subsided back into the ocean Ex: Bikini Atoll, Lighthouse reef, Motu Iti
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Coastal Features CB-4C8E-8AF7-45F1B0F0ADA0
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Peninsula A piece of land almost completely surrounded by water
Formed by coastal erosion Ex: Florida, Italy
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Delta Alluvial deposit at the mouth of the river
Form from deposition of sediment carried by a river as the flow leaves its mouth. Ex: Mississippi River Delta
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Submarine Canyon Deep canyon cut into the continental shelf and slope, often found at the mouth of a river Carved by turbidity currents created by rivers or deltas Ex: Alvies Canyon in the Bay of Biscay in Spain
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Cape (Headland) Coastal landform that extends out into a body of water
Formed by coastal erosion Ex: Cape Fear
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Bay Inlet of the sea Formed as softer rock erodes while more resistant rock does not forming a headland Ex: Galveston Bay, Chesapeake Bay
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