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-3524-4872-9335-94E264BD51C4

Ocean Floor Provinces Continental Margins Deep Ocean Basins 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 Active 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 Transform 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