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2.00 Bathmetry Lecture notes Bathymetry of the Ocean Floor Text Book Reading Pages – 37 - 42 The ocean floor is mapped by SONAR. (______________________________________________________________) Depth = (time x 1500 m/sec)/2 (round trip) At ____________ degrees Celsius Relationship above and below the water Ocean Floor Topography Major features: ___continental shelf, ___trenches, ___abyssal plains, ____mid-ocean ridges. After 1920’s, these features could be mapped in detail by sonar (bouncing sound waves off the ocean floor). 2.00 Bathmetry Lecture notes ______________________________________ +Area of shallow water along ___________________ continental margin (not an active plate boundary). +Shelf drops off abruptly at outer edge. +Much of shelf was above sea level during past __________________ periods. Important processes at a passive margin Accumulation of ______________________. Subsidence (_______________) of crust as sediment is added. Mass wasting at edge of continental shelf. Turbidity currents (large rapid flows of dense, sediment-laden water). ______________________________________ +gentle slope at the base of the continental slope caused by: - turbidity currents - deposition of sediment by underwater landslides and other processes that carry mud, sand & silt down the slope - occurs at the ______________ of the slopes & gently slope seaward to the deep sea floor __________________________________ +Occur along active margins (present-day plate boundaries) where _________________________ is taking place +deepest part of the ocean floor, typically 3 - 4 km deeper than surrounding seafloor +relatively narrow, few 10’s of km wide and thousands of km long +most occur in the Pacific, mostly western Pacific, but most of the Pacific is surrounded by trenches +deepest spot in the oceans is the Challenger Deep in the _____________________ Trench, 11,035 m +trenches are associated with ____________ volcanoes and earthquakes -most are near chains of volcanic islands Abyssal Plane +_________________________ making up much of the ocean floor apart from trenches and mid-ocean ridges Mid-Ocean Ridges +_____________________________ features on earth. +Broad ridges with a deep rift valley down the center. +Offset by faults. +Location where basaltic lava flows erupt. +Age of the ocean floor 2.00 Bathmetry Lecture notes -Detailed studies in 1950’s showed that there are bands of similar aged rocks parallel to mid-ocean ridges. -Bands get older with greater distance from the ridges. ________________________ - ripple marks observed on the floor of submerged canyons and sediments fanning out at the end suggest they were formed by moving sediments and water - cut by turbidity currents - caused by earthquakes or buildup of sediment on a steep slope - fast moving avalanches of mud, sand and water that flow down slope, erode walls and pick up sediment - as flow reaches bottom, it slows down, fans out and the sediment settles out __________________________ cut through the shelves and slopes, look like river valleys on land, cut during periods of low sea level by turbidity currents, some associated with major rivers, e.g. Hudson Canyon Ocean Floor is seaward of the continental margin covers 30% of the earth's surface compared to 29% covered by the continents - in most places, seafloor is a flat plain Abyssal Plain +covered by sediment deposits of turbidity currents +covering an irregular seafloor plain interrupted by: _________________________ (< 1 km above the seafloor) - cover -80% of the Pacific and -50% of the Atlantic sea mounts (rise steeply, sometimes above the surface to form islands) _________________________ (flat topped seamounts found most often in the Pacific) __________________________, usually I - 1.7 km below the surface - many have ancient coral reefs on top indicating that they were once at the surface - flat tops due to wind & rain erosion - subsided due to their own weight & crustal movement Basins Abyssal plains Abyssal hill Seamount Guyot Trenches Mid Ocean ridges Rift Valley