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Unformatted text preview: bathymetry Continental Margins & Ocean Basins technology key features of ocean floor topography active / passive margins continental shelf continental slope continental rise abyssal plains ridge system seamounts ocean basin turbidity currents submarine canyons atolls / guyots trench
Fig. 4-22, p. 115 How to map the seafloor? old school: rope Echo sounder (aka Sonar) complications ship moving sound speed varies
Beam of sound waves travels to bottom and is reflected back to ship Multibeam sonar system Depth = V (T/2) Fig. 4-2a, p. 100 ABE traverse and bathymetric data example ABE: Autonomous Benthic Explorer
Box 4-1a, p. 102 Box 4-1b, p. 103 1 Satellite altimetry measures variations in sea surface height with ~1 inch precision pull of gravity on water varies depending on proximity to more "massive" geologic features ex: underwater volcano 2,000 m tall and 20 km wide would produce a 2 m rise in the surface water Geosat, TPOEX/Poseidon, Jason-1
Fig. 4-5c, p. 104 Submarine Crash Shows Navy Had Gaps in Mapping System
By CHRISTOPHER DREW Published: January 15, 2005
Sailors on the San Francisco, a nuclear-powered attack submarine, had just finished cleaning nuclearthe vessel last Saturday as it sped along 500 feet beneath the surface of the South Pacific. surface Submarines run blind, just listening for sounds of danger. And to the captain and other officers to relying on undersea navigation charts, everything seemed clear. Suddenly, there was a horrible screeching. And according to an e-mail message written by a ecrew member, the inside of the submarine quickly resembled a scene from the movie "The scene Matrix." He wrote, "Everything slowed down and levitated and then went flying forward faster then than the brain can process." The submarine had crashed head-on into an undersea mountain that was not on the charts. headOne sailor was killed, and about 60 others were injured. Now, Defense Department officials say Defense they have found a satellite image taken in 1999 that indicates an undersea mountain rising to an perhaps within 100 feet below the surface there. "The U.S.S. San Francisco was in the area of the Caroline Ridge," said Lt. Ridge," Commander Davis. The Caroline Ridge is east of Palau and Yap, intersecting the Yap Trench from the east, and consists of a chain of chain seamounts. Hypsographic curve avg depth of ocean much deeper than avg height of land above sealevel deepest ocean ~11 km vs highest mountain 8.85 km result of tectonic processes and crustal composition Pacific 4028 m Atlantic 3332 m Indian 3897 m
Fig. 4-22, p. 115 2 Continental margin slope: steep descent shelf: outer edge of continent 10's 100's km wide 10' 100' rise: gradual descent 0 130 m deep (avg 60m) (avg (9m/km) underlain by continental crust / sediment Percentage of Earth surface that is... Fig. 4-8, p. 106 Fig. 4-9, p. 106 Passive continental margin "Atlantic" type Fig. 4-6, p. 105 Gulf of Mexico: south of TX Broad continental shelf Passive Margin "Atlantic type"
ex: Hudson Canyon east of New Jersey face divergent plate boundary broad shelf (>350 km wide) not tectonically active abundant sedimentation character determined by seds less-steep continental slope Fig. 4-17, p. 111 3 Active margin- "Pacific" type face or near edge of convergent plate boundaries narrow less sediment character determined by faulting, volcanism, tectonic deformation complex steeper continental slope Continental shelf west of central California active margin Fig. 4-10, p. 107 Changes in sea level over the last 250,000 years last glacial maximum "ice age" (18,000 yrs ago)- seawater locked up in ice sealevel ~125 m lower than today exposed much of shelf Sea level rise in southern Florida if the Greenland Ice Sheet melts. Red areas in this image show locations susceptible to a five-meter rise of sea level, based on elevation. Yellow areas denote urban locations
http://www.geo.arizona.edu/dgesl/research/other/climate_change_and_sea_level/rising_sea_levels.htm Fig. 4-15, p. 110 Submarine canyons at shelf break "V" shaped canyons some deeper than Grand Canyon major avalanches (aka turbidity currents) triggered by earthquakes or overloading of sediments seds supplied by rivers and currents turbidity currents create fan-shaped sediment piles Fig. 4-16, p. 111 Fig. 4-19, p. 112 4 Ocean basin floor seaward of the continental margin Abyssal Plain broad flat regions built by sediments 41% of ocean floor sediment up to 5 km thick relatively featureless Abyssal plain Abyssal hills gentle slopes <1000 m high Fig. 4-28, p. 120 underwater volcanoes steep slopes very tall (>5 km) can grow to form Islands (ex: Hawaii) "Guyot" seamount with flat Guyot" top because it was once above sea level and was eroded related to hot spots or convergent margins Seamounts Kavachi_eruption.mov Vailulu'u easternmost "island" of the Samoan chain rises >4000 m from ocean floor actively growing!
Fig. 4-29b, p. 121 Atolls island built of coral reef on flat-topped flatseamount ring-shaped reef ringlagoon in the middle mostly found in the western Pacific & Indian Ocean highly susceptible to sea level / climate change! ex: Tuvalu (avg elevation: 4.6 m (~15 ft) above s.l.) (avg s.l.) entire country (only <10 m2 of land) being evacuated > 10,000 global change refugees Funafuti, Tuvalu 5 Ridges and Rises series of volcanic mountain chains "Ridge" steeper slope- Atlantic Ridge" slope "Rise" gentler slope- Pacific Rise" slopetotal length = 65,000 km ~22% of ocean floor width: ~1000 km height: ~1000-2000 m ~1000Features rift valley fracture zones hydrothermal vents
Fig. 4-29a, p. 120 Variations in Mid-Ocean Ridge systems Rates of spreading at world's Mid-Ocean Ridges (in cm/yr) East Pacific Rise ~ 6X faster than Mid-Atlantic Ridge Atlantic slower spreading steeper topography more sediment accumulation Pacific faster less topography less sediment Fig. 4-21a, p. 114 Ocean trenches of the world http://www.ngdc.noaa.gov/mgg/image/marianas.html Fig. 4-30, p. 122 Fig. 4-31, p. 123 6 You should be able to locate... locate... continental shelf shelf break abyssal plains mid-ocean ridges mid seamounts hotspots trenches ... and be able to explain why they are located where they are, in relation to the tectonic setting ... Fig. 4-32, pp. 124-125 7 ...
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This note was uploaded on 04/29/2008 for the course EAS 104 taught by Professor Brown during the Spring '08 term at Purdue University-West Lafayette.
- Spring '08