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© 2011 Pearson Education, Inc. CHAPTER 3 Marine Provinces
© 2011 Pearson Education, Inc. Chapter Overview The study of bathymetry charts ocean depths and ocean floor topography. Echo sounding and satellites are efficient bathymetric tools. Most ocean floor features are generated by plate tectonic processes.
© 2011 Pearson Education, Inc. Bathymetry Measures the vertical distance from the ocean surface to mountains, valleys, plains, and other sea floor features
© 2011 Pearson Education, Inc. Measuring Bathymetry Soundings –Poseidonus first sounding 85 B.C. –Line with heavy weight –Sounding lines used for 2000 years Unit of measure is a fathom –1.8 meters (6 feet) First systematic measurements – HMS Challenger 1872
© 2011 Pearson Education, Inc. Measuring Bathymetry Echo Soundings –Echo sounder or fathometer –Reflection of sound signals –German ship Meteor identified mid-Atlantic ridge in 1925 Lacks detail May provide inaccurate view of sea floor
© 2011 Pearson Education, Inc. Echo Sounding Record
© 2011 Pearson Education, Inc. Measuring Bathymetry Precision Depth Recorder (PDR) –1950s –Focused high frequency sound beam –First reliable sea floor maps produced –Helped confirm sea floor spreading
© 2011 Pearson Education, Inc. Measuring Bathymetry Modern Acoustic Instruments Side scan sonar –GLORIA (Geological Long-range Inclined Acoustical instrument) –Sea MARC (Sea Mapping and Remote Characterization) Can be towed behind ship to provide very detailed bathymetric strip map Multi-beam echo sounder –Seabeam
© 2011 Pearson Education, Inc. Side Scanning Sonar
© 2011 Pearson Education, Inc. Sea Floor Mapping from Space Uses satellite measurements Measures sea floor features based on gravitational bulges in sea surface Indirectly reveals bathymetry
© 2011 Pearson Education, Inc. Measuring Bathymetry Seismic Reflection Profiles –Air guns –Strong, low-frequency sounds –Details ocean structure beneath sea floor
© 2011 Pearson Education, Inc. Seismic Reflection Profile
© 2011 Pearson Education, Inc. Hypsographic Curve Shows relationship between height of land and depth of ocean
© 2011 Pearson Education, Inc. Hypsographic Curve 70.8% of Earth covered by oceans Average ocean depth is 3729 meters Average land elevation is 840 meters Uneven distribution of areas of different depths/elevations Variations suggest plate tectonics at work
© 2011 Pearson Education, Inc. Ocean Provinces Three Major Provinces Continental margins –Shallow-water areas close to shore Deep-ocean basins –Deep-water areas farther from land Mid-ocean ridge –Submarine mountain range
© 2011 Pearson Education, Inc. Ocean Provinces
© 2011 Pearson Education, Inc. Continental Margins Passive or Active Passive –Not close to any plate boundary –No major tectonic activity –Example: East coast of United States Active –Associated with convergent or transform plate boundaries –Much tectonic activity
© 2011 Pearson Education, Inc. Active Continental Margins Convergent or Transform Convergent Active Margin –Oceanic-continent convergent plate boundaries –Active continental volcanoes –Narrow shelf –Offshore trench –Example: Western South America
© 2011 Pearson Education, Inc. Active Continental Margins Transform Continental Margin –Less common –Transform plate boundaries –Linear islands, banks, and deep basins close to shore –Example: Coastal California along San Andreas Fault
© 2011 Pearson Education, Inc. Passive and Active Continental Margins
© 2011 Pearson Education, Inc. Continental Margin Features Continental shelf Shelf break Continental slope Continental rise
© 2011 Pearson Education, Inc. Passive Continental Margin Features
© 2011 Pearson Education, Inc. Continental Shelf Flat zone from shore to shelf break –Shelf break is where marked increase in slope angle occurs Geologically part of continent Average width is 70 km (43 miles) but can extend to 1500 km (930 miles) Average depth of shelf break is 135 meters (443 feet)
© 2011 Pearson Education, Inc. Continental Shelf The type of continetnal margin determines the shelf features. Passive margins have wider shelves. California’s transform active margin has a continental borderland.
© 2011 Pearson Education, Inc. Continental Slope Where deep ocean basins begin Topography similar to land mountain ranges Greater slope than continental shelf –Averages 4 ° but varies from 1–25 ° gradient Marked by submarine canyons
© 2011 Pearson Education, Inc. Submarine Canyons Narrow, deep, v-shaped in profile Steep to overhanging walls Extend to base of continental slope, 3500 meters (11,500 feet) below sea level. Carved by turbidity currents
© 2011 Pearson Education, Inc. Turbidity Currents Underwater avalanches mixed with rocks and other debris Sediment from continental shelf Moves under influence of gravity Sediments deposited at slope base
© 2011 Pearson Education, Inc. Continental Rise Transition between continental crust and oceanic crust Marked by turbidite deposits from turbidity currents Graded bedding in turbidite deposits Deposits generate deep-sea fans, or submarine fans Distal ends of submarine fans becomes flat abyssal plains
© 2011 Pearson Education, Inc. Abyssal Plains Extend from base of continental rise Some of the deepest, flattest parts of Earth Suspension settling of very fine particles Sediments cover ocean crust irregularities Well-developed in Atlantic and Indian oceans
© 2011 Pearson Education, Inc. Abyssal Plains
© 2011 Pearson Education, Inc. Abyssal Plain Volcanic Peaks Poke through sediment cover Below sea level: –Seamounts, tablemounts, or guyots at least 1 km (0.6 mile) above sea floor –Abyssal hills or seaknolls are less than 1 km (0.6 mile) above sea floor Above sea level: –Volcanic islands
© 2011 Pearson Education, Inc. Ocean Trenches and Volcanic Arcs Convergent margins generate ocean trenches. –Deepest part of oceans –Most in Pacific Ocean –Deepest trench – Mariana Trench at 11,022 meters (36,161 feet) Volcanic arc on nonsubducted ocean plate –May produce island arc, e.g., Japan Continental arc on land
© 2011 Pearson Education, Inc. Pacific Ring of Fire Margins of Pacific Ocean Majority of world’s active volcanoes and earthquakes Marked by convergent boundaries
© 2011 Pearson Education, Inc. Ocean Trenches and Ring of Fire
© 2011 Pearson Education, Inc. Mid-Ocean Ridge Longest mountain chain On average, 2.5 km (1.5 miles) above surrounding sea floor Wholly volcanic Basaltic lava Divergent plate boundary
© 2011 Pearson Education, Inc. Mid-Ocean Ridge
© 2011 Pearson Education, Inc. Mid-Ocean Ridge Features Central rift valley downdropped by seafloor spreading –Fissures and faults in rift valley Seamounts – tall volcanoes Pillow lava or pillow basalt – shapes formed when hot basaltic lava quickly cools
© 2011 Pearson Education, Inc. Mid-Ocean Ridge Features SeamountPillow lava
© 2011 Pearson Education, Inc. Mid-ocean Ridge Features Hydrothermal Vents Sea floor hot springs Foster unusual deep-ocean ecosystems able to survive without sunlight Warm water vents – temperatures below 30 ° C (86 ° F) White smokers – temperatures from 30–350 ° C (86–662 ° F) Black smokers – temperatures above 350 ° C (662 ° F)
© 2011 Pearson Education, Inc. Hydrothermal Vents
© 2011 Pearson Education, Inc. Fracture Zones and Transform Faults
© 2011 Pearson Education, Inc. Transform Faults and Fracture Zones
© 2011 Pearson Education, Inc. Oceanic Islands Volcanic activity Hotspots Island arcs
© 2011 Pearson Education, Inc. End of CHAPTER 3 Marine Provinces
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