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Transcript
Ocean Features Bathymetry Bathymetry-(Bathos=depth;metry- measurement) Measurement of ocean depths and charting the shape of the ocean floor Sounding- Using a line with heavy weight to probe ocean’s depths – Fathom- unit of measurement specifically for ocean depth measurement (1 fathom=1.8 meters=6 feet) HMS Challenger 1872- made first systematic measurements using sounding technology Noticed that depth varied indicating that the ocean floor was not flat, but had relief just as land does Advancing Technology SONAR Technology- Sound, Navigation, And Range 1900s- Echo Sounders – Sends a sound signal to determine depth and shape of ocean floor. Early technology not very accurate 1950s- Precision Depth Recorder (PDR) – Used high-frequency sound beam to measure depths within 1 meter accuracy Current technology- Multibeam Echo Sounders – Use multiple frequencies of sound simultaneously giving more precise data http://player.discoveryeducation.com/index.cfm? guidAssetId=933F96EA-3524-4872-933594E264BD51C4 Ocean Floor Provinces Continental Margins – Shallow water areas close to continents Deep Ocean Basins – Deep water areas farther from land Mid-Ocean Ridge – Shallower areas near the middle of the ocean Continental Margins Passive Margins – Imbedded within the interior of lithospheric plates and are not in close proximity to plate margins – Lack tectonic activity Active Margins – Associated with lithospheric plate boundaries and are marked by a high degree of tectonic activity Active Margins Convergent Active margins – oceanic-continental convergent plate boundaries – Features Continental arc, narrow shelf, steep slope, offshore trench Transform Active margins – Transform plate boundaries – Faults create linear islands, banks, deep basins Features of Continental Margins Continental shelf- flat zone extending from the shore beneath the ocean to a point where slope angle increases dramatically – Average width- 70 KM – Ranges from a meters to 1500 KM Shelf Break- Point where increase in slope angle occurs – Can contain coastal islands, reefs, and raised banks Features of Continental Margins Continental borderland- occurs in faulted areas (California). High degree of relief on shelf Continental slope- this is where deep ocean basins begin Continental rise- transition zone between the continental margin and the deep ocean floor – Graded bedding, produced by turbidity currents. Layered sedimentation with heavier sediments settling out first. Decrease in sediment size from bottom to top Underwater Canyons Submarine canyons- V-shaped and have branches or tributaries with steep overhanging walls – Thought to occur because of turbidity currents – Turbidity currents- Underwater avalanches of muddy water mixed with rocks and other debris – Mass moves from earthquakes, hurricanes, or other disturbance carving the canyon Deep Ocean Abyssal Plains- Extend from the base of the continental rise into the deep-ocean basins. – Flat, depositional surfaces with very slight slopes – Average between 4500 meters and 6000 meters deep – Suspension Settling- fine particles of sediment slowly drift onto the deep ocean floor This is how abyssal plains form Underwater Volcanoes Seamounts: Below sea level, but rise 1 kilometer above the deep ocean floor Seaknolls (abyssal hills) less than 1 kilometer above the deep ocean floor Ocean Trenches Deep linear scars in the ocean floor. They are very narrow and steep Occurs along active continental margins, where there is a convergent plate boundary The side nearest to land can be volcanic arcs (islands of Japan), or continental arcs (Andes Mountains) Mid-Ocean Ridge Earth’s longest mountain chain – 75,000 kilometers/46,600 miles Divergent boundary Entirely volcanic- composed of basaltic lavas Rift valley occurs along its crest Underwater lava flows- Pillow lavas Hydrothermal Vents Hot springs which occur in the central rift valley Appearance depends on temperature of water – Warm-water vents are below 30oC (86oF) and are clear in color – White smokers are between 30oC and 350oC (86oF- 662oF) and are white in color – Black smokers are above 350oC (662oF) and are black in color Mid-Ocean Ridge cont. Oceanic ridges have a rift valley and steep rugged slopes Oceanic rises have slopes that are gentler and less rugged Mid-Ocean Ridge Transform Faults cut the mid-ocean ridge in a number of places – These faults are perpendicular to the mid-ocean ridge and give the ridge a zigzag appearance – Many earthquakes occur here Fracture Zones also extend from the mid-ocean ridge, but are much different from transform faults