3: The Ocean Floor Part 2

3: The Ocean Floor Part 2

1. the layers of the ocean crust are created at the eruptive center of the mid-ocean ridge

   • gabbro crystalizes on the edge of the magma chamber

2. oceanic crust is fairly young on this planet

   • the oldest oceanic crust is beneath the meditteranean
     • about 280 million years old
   • else has been destroyed
     • turned into an ophealite
     • subducted

3. trenches

   • june 19th, 1874
     • USS Tuscarora discovered
   • march 23rd 1875
     • HMS challenger found marianna trench
       • deepest part of ocean: 11,033 meters deep
         • 1960: Trieste (french exploration)
           • 10,916 m
           • 1995: Kaiko
             • 10,911 m
             • 2009: Nereus
               • 10,902 m
               • 2012: Deepsea Challenger
                 • 10,898 m
                 • funded privately; engineered to withstand pressure

4. seamounts

   • elevational heights on sea floors (underwater mountains)
     • stick out on top: "islands"
     • any mount >1000 meters from seafloor
   • guyot: flat-topped
   • formation
     • big cones of pillow lavas, building up over time from eruptions
       • active today; may reach surface--island ex: hawaii
         • island erodes by ocean -- becomes flat plateau from waves
           • ex: island of midways
           • oceanic crust: older it gets, colder, heavier/denser sinks deeper
             • also ocean level rises
               • = guyot formation
   • island chains
     • ex: hawaiian seamounts
       • no where near plate boundary...(where are the volcanos?)
         • hot spots
           • base of lithosphere: regionally very hot: produces localized melt
             • "mantle plume" cooks from beneath mantle, sends lava through it
           • as the plate moves over mantle plume, creates a series of new volcanoes as magma punches plate
             • = "hot spot trail/chain"
           • ex: emporer seamounts
             • until 43 million ya pacificplate moves almost exactly due north to subduct under north american plate
               • then plate turned westward
                 • volcanic islands continued to form: emporer and hawaiian seamounts
                   • as a result of subsidence and erosion: most of seamounts are now below sea level
           • cause of hotspots: unknown