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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- Summer '07
- Plate Tectonics, Continental shelf, 4 km, 500 m, 4.5 km