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GEOL 101 pg 622-626 outline

GEOL 101 pg 622-626 outline - floor spreading begins –...

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February 10 – 622-626 Landscapes Beneath the Sea Oceans exist because oceanic lithosphere and continental lithosphere differ remarkedly in terms of composition and thickness. The surface of the denser and thinner oceanic lithosphere lies deeper than the surface of the buoyant and thicker continental lithosphere, creating oceanic basins that fill with water. Continental shelves, slopes, and rises Continental shelf – relatively shallow portion of the ocean in which water depth does not exceed 500 m. The continental shelf merges with the continental slope, which descends to depths of nearly 4 km. From 4 km to 4.5 km, a province called continental rise, there is a vast, nearly horizontal plain – ABYSSAL PLAIN Continental shelves form along PASSIVE CONTINENTAL MARGINS: margins that are not plate boundaries and thus lack seismicity. They originate after rifting breaks a continent in two; when rifting stops, sea
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Unformatted text preview: floor spreading begins – the stretched lithosphere at the boundary between the ocean and continent cools and sinks. ACTIVE CONTINENTAL MARGIN, a margin that coincides with a plate boundary thus hosts many earthquakes. Abyssal Plains and Seamounts As oceanic crust moves away from mid-ocean ridges, a blanket of PELAGIC SEDIMENT accumulates and covers the basalt of the oceanic crust. As time goes on, sediment thickness increases away from the ridge axis. Over time, the sediment buries the escarpments that had formed at the mid-ocean ridges, resulting in a flat, featureless surface of the abyssal plain. If areas protrude above sea level from hot-spot volcanic activity, it forms an oceanic island. Oceanic islands host active volcanoes. With time, oceanic islands erode and partially collapse due to slumping. The seafloor beneath them ages and sinks. What was once an island becomes an seamount....
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