Once the ice sheets melt the weight of the ice is

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Once the ice sheets melt, the weight of the ice is removed and the crust may rise Crustal Rebound = rise of crustal lithosphere after removal of ice Chapter 18 Over 70% of Earth’s surface is covered by oceans Passive Continental Margin Geologically quiet (i.e., no plate boundaries) Contain continental shelf, continental slope, continental rise, and abyssal plain Sediment deposited via turbidity currents and by contour currents Active Continental Margin Geologically active with plate boundaries leading to earthquakes, young mountain belts, and volcanoes Lacks continental rise and abyssal plain Ocean Trench: narrow, deep trough parallel to the edge of a continent or an island arc o Deepest parts of the oceans o Upper Benioff Zone o Low heat flow o Negative gravity anomalies Mid-Ocean Ridge : Giant undersea mountain range extending around the world like the seams on a baseball Made mostly of young basalt flows A rift valley runs down the crest of the ridge Shallow focus earthquakes Extremely high heat flow Often marked by line of hot springs, supporting unique biological communities Offset along transform fracture zones (major lines of weakness in the crust that cross mid- ocean ridges at approximately right angles)
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Seamounts - conical undersea mountains that rise 1000 meters or more above the sea floor Most are extinct volcanoes (except near mid-ocean ridge or hot spot) Chains of seamounts form aseismic ridges (no earthquakes) Types of Reefs Reefs : wave-resistant ridges of coral, algae, and other calcareous organisms (calcium carbonate anatomical structures) Fringing Reefs : flat, table-like reefs attached directly to short Barrier Reefs : parallel to the short but are separated by wide, deep lagoons Atolls : circular reefs that rim lagoons All rocks & sediments of the deep sea floor are less than 200 million years old Continents preserve rocks up to 4 billion years old Chapter 19 Theory of Plate Tectonics Earth’s surface is composed of a few large, thick plates that move slowly and change in size Rejection of Wegner’s continental drift- he could not explain how the continents could have moved Vine-Matthews hypothesis- the first scientific test of the seafloor spreading theory of continental drift & plate tectonics Tectonics of the Red Sea Causes of plate motion Ridge Push – sliding of lithosphere away from ridge crest, along slope due to gravity Slab Pull – subducting lithosphere pulls plate away from ridge crest Trench Suction – steep subduction can cause overlying plate to be pulled horizontally Mantle Convection – may be cause or effect of plate tectonics, either way closely related to plate movement
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