chapter_18_powerpt.CM-11e

chapter_18_powerpt.CM-11e - The Sea Floor Physical Geology...

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Steve Kadel, Glendale Community College The Sea Floor Physical Geology 11/e, Chapter 18
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The Water Planet Over 70% of Earth’s surface is covered by oceans Prior to 1950, little was known about the deep ocean floor Oceans originated primarily from volcanic degassing of water vapor from Earth’s interior Small additional amount of water may have come from comets impacting the Earth
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Studying the Sea Floor Sea floor rocks are quite widespread, but difficult to study Sea floor rocks and sediments sampled using rock dredges , seafloor drilling , or submersibles Indirect observations of the sea floor with sonar and seismic reflection profiling Fig. 18.1
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Studying the Sea Floor Samples of rock and sediments can be taken from the sea floor in several ways A Rock Dredge – an open steel container is dragged over the ocean bottom at the end of a cable Seafloor Drilling – a study ship can drill a hole in the deep-sea ocean floor – Cuts rock cores and sediment cores Submersibles – can sample the sea floor and provide observation for geologists (directly or remotely) – photographs
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Studying the Sea Floor Sonar and similar systems Single-beam echo sounder – measures water depth and draws profiles of submarine topography (invented in 1920) A sound wave is sent downward from a ship, bounces off the sea floor, and returns to the ship – a clock precisely measures the time interval to fractions of a second Water depth is determined from the time it takes the sound wave to make the round trip Multibeam sonar – sends out and records an array of sound sources and listening devices Sidescan sonar – measures the intensity of sound reflected back to the vessel from the sea floor to provide detailed images of the sea floor and other data from the sea floor
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Fig. 18.4 Fig. 18.4 Diagram showing how echo sounding, seismic reflection, and sidescan sonar are used to study the sea floor.
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Studying the Sea Floor Sonar and similar systems Seismic reflection profiler – essentially the same principles as the echo sounders but uses a louder noise at lower frequency Magnetic, gravity, and seismic refraction surveys – can be pulled behind ships to provide some details of the sea floor Satellites – use radar altimeters to measure subtle differences of the ocean surface Small variations reflect the gravitational pull of features on the sea floor (From Tarbuck & Lutgens, 8e)
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A Satellite Altimeter (From Tarbuck & Lutgens, 8e)
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Features of the Sea Floor Passive continental margins have a continental shelf , continental slope , and continental rise descending to the extremely flat deep ocean floor of the abyssal plain Active continental margins , which are associated with numerous earthquakes and active volcanoes, have continental shelves and
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chapter_18_powerpt.CM-11e - The Sea Floor Physical Geology...

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