15. V = speed of sound in water (about 1.5 km/sec) T = time Echo sounders sense the contour of the seafloor by beaming sound waves to the bottom and measuring the time required for the sound waves to bounce back to the ship.
50. How do submarine canyons form? Submarine canyons cut into the continental shelf and slope, often terminating on the deep-sea floor in a fan-shaped wedge of sediment.
51. Submarine cables near Nova Scotia, Canada http://www.geol.lsu.edu/Faculty/Juan/PhysicalGeology_F2004/images/Turbidity2.gif
52.
53. turbidity current an underwater “avalanche” of sediment http://unit.aist.go.jp/igg/rg/igi-rg/beta/sl-support/R-formation/TurbidityCurrent.jpg Most geologists believe that submarine canyons have been formed by abrasive turbidity currents plunging down the canyons.
66. Hydrothermal vents are common on oceanic ridges http://www.nature.com/nature/journal/v439/n7079/images/hydro_vents/index.html AND in freshwater (Lake Baikal)
76. Sampling of the world's deepest sea sediment by " Kaiko " at the Mariana Trench, Challenger Deep Bacteria collected from the Mariana Trench
77.
78. Key Points 1. The ocean floor is mapped by bathymetry . 2. Ocean-floor topography varies with location . 3. Continental margins are “active” or “passive”. 4. The topology of deep-ocean basins differs from that of the continental margin.